1. 13 Jun, 2017 1 commit
  2. 23 Apr, 2017 1 commit
    • Ingo Molnar's avatar
      Revert "x86/mm/gup: Switch GUP to the generic get_user_page_fast() implementation" · 6dd29b3d
      Ingo Molnar authored
      This reverts commit 2947ba05.
      Dan Williams reported dax-pmem kernel warnings with the following signature:
         WARNING: CPU: 8 PID: 245 at lib/percpu-refcount.c:155 percpu_ref_switch_to_atomic_rcu+0x1f5/0x200
         percpu ref (dax_pmem_percpu_release [dax_pmem]) <= 0 (0) after switching to atomic
      ... and bisected it to this commit, which suggests possible memory corruption
      caused by the x86 fast-GUP conversion.
      He also pointed out:
        This is similar to the backtrace when we were not properly handling
        pud faults and was fixed with this commit: 220ced16
       "mm: fix
        get_user_pages() vs device-dax pud mappings"
        I've found some missing _devmap checks in the generic
        get_user_pages_fast() path, but this does not fix the regression
      So given that there are known bugs, and a pretty robust looking bisection
      points to this commit suggesting that are unknown bugs in the conversion
      as well, revert it for the time being - we'll re-try in v4.13.
      Reported-by: default avatarDan Williams <dan.j.williams@intel.com>
      Cc: Andrew Morton <akpm@linux-foundation.org>
      Cc: Borislav Petkov <bp@alien8.de>
      Cc: Catalin Marinas <catalin.marinas@arm.com>
      Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
      Cc: Linus Torvalds <torvalds@linux-foundation.org>
      Cc: Michal Hocko <mhocko@suse.cz>
      Cc: Peter Zijlstra <peterz@infradead.org>
      Cc: Rik van Riel <riel@redhat.com>
      Cc: Thomas Gleixner <tglx@linutronix.de>
      Cc: aneesh.kumar@linux.vnet.ibm.com
      Cc: dann.frazier@canonical.com
      Cc: dave.hansen@intel.com
      Cc: steve.capper@linaro.org
      Cc: linux-kernel@vger.kernel.org
      Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
  3. 04 Apr, 2017 1 commit
  4. 27 Mar, 2017 1 commit
  5. 21 Mar, 2017 1 commit
    • Thomas Garnier's avatar
      x86/headers: Simplify asm/fixmap.h inclusion into asm/pgtable*.h · ef37bc36
      Thomas Garnier authored
      Instead of including fixmap.h twice in pgtable_32.h and pgtable_64.h,
      include it only once, in the common asm/pgtable.h header.
      Signed-off-by: default avatarThomas Garnier <thgarnie@google.com>
      Cc: Alexander Potapenko <glider@google.com>
      Cc: Andrew Morton <akpm@linux-foundation.org>
      Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
      Cc: Andy Lutomirski <luto@kernel.org>
      Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
      Cc: Borislav Petkov <bp@suse.de>
      Cc: Chris Wilson <chris@chris-wilson.co.uk>
      Cc: Dave Hansen <dave.hansen@linux.intel.com>
      Cc: Dmitry Vyukov <dvyukov@google.com>
      Cc: Hugh Dickins <hughd@google.com>
      Cc: Kees Cook <keescook@chromium.org>
      Cc: Linus Torvalds <torvalds@linux-foundation.org>
      Cc: Matthew Wilcox <willy@linux.intel.com>
      Cc: Michal Hocko <mhocko@suse.com>
      Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
      Cc: Peter Zijlstra <peterz@infradead.org>
      Cc: Thomas Gleixner <tglx@linutronix.de>
      Cc: Xiao Guangrong <guangrong.xiao@linux.intel.com>
      Cc: kasan-dev@googlegroups.com
      Cc: kernel-hardening@lists.openwall.com
      Cc: linux-mm@kvack.org
      Cc: richard.weiyang@gmail.com
      Cc: zijun_hu <zijun_hu@htc.com>
      Link: http://lkml.kernel.org/r/20170321071725.GA15782@gmail.com
      [ Generated this patch from two other patches and wrote changelog. ]
      Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
  6. 18 Mar, 2017 2 commits
  7. 25 Feb, 2017 1 commit
  8. 15 Dec, 2016 1 commit
  9. 11 Aug, 2016 1 commit
    • Dave Hansen's avatar
      x86/mm: Fix swap entry comment and macro · ace7fab7
      Dave Hansen authored
      A recent patch changed the format of a swap PTE.
      The comment explaining the format of the swap PTE is wrong about
      the bits used for the swap type field.  Amusingly, the ASCII art
      and the patch description are correct, but the comment itself
      is wrong.
      As I was looking at this, I also noticed that the
      SWP_OFFSET_FIRST_BIT has an off-by-one error.  This does not
      really hurt anything.  It just wasted a bit of space in the PTE,
      giving us 2^59 bytes of addressable space in our swapfiles
      instead of 2^60.  But, it doesn't match with the comments, and it
      wastes a bit of space, so fix it.
      Signed-off-by: default avatarDave Hansen <dave.hansen@linux.intel.com>
      Cc: Andrew Morton <akpm@linux-foundation.org>
      Cc: Andy Lutomirski <luto@kernel.org>
      Cc: Borislav Petkov <bp@alien8.de>
      Cc: Brian Gerst <brgerst@gmail.com>
      Cc: Dave Hansen <dave@sr71.net>
      Cc: Denys Vlasenko <dvlasenk@redhat.com>
      Cc: H. Peter Anvin <hpa@zytor.com>
      Cc: Josh Poimboeuf <jpoimboe@redhat.com>
      Cc: Linus Torvalds <torvalds@linux-foundation.org>
      Cc: Luis R. Rodriguez <mcgrof@suse.com>
      Cc: Peter Zijlstra <peterz@infradead.org>
      Cc: Thomas Gleixner <tglx@linutronix.de>
      Cc: Toshi Kani <toshi.kani@hp.com>
      Fixes: 00839ee3 ("x86/mm: Move swap offset/type up in PTE to work around erratum")
      Link: http://lkml.kernel.org/r/20160810172325.E56AD7DA@viggo.jf.intel.com
      Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
  10. 13 Jul, 2016 1 commit
    • Dave Hansen's avatar
      x86/mm: Move swap offset/type up in PTE to work around erratum · 00839ee3
      Dave Hansen authored
      This erratum can result in Accessed/Dirty getting set by the hardware
      when we do not expect them to be (on !Present PTEs).
      Instead of trying to fix them up after this happens, we just
      allow the bits to get set and try to ignore them.  We do this by
      shifting the layout of the bits we use for swap offset/type in
      our 64-bit PTEs.
      It looks like this:
       bitnrs: |     ...            | 11| 10|  9|8|7|6|5| 4| 3|2|1|0|
       names:  |     ...            |SW3|SW2|SW1|G|L|D|A|CD|WT|U|W|P|
       before: |         OFFSET (9-63)          |0|X|X| TYPE(1-5) |0|
        after: | OFFSET (14-63)  |  TYPE (9-13) |0|X|X|X| X| X|X|X|0|
      Note that D was already a don't care (X) even before.  We just
      move TYPE up and turn its old spot (which could be hit by the
      A bit) into all don't cares.
      We take 5 bits away from the offset, but that still leaves us
      with 50 bits which lets us index into a 62-bit swapfile (4 EiB).
      I think that's probably fine for the moment.  We could
      theoretically reclaim 5 of the bits (1, 2, 3, 4, 7) but it
      doesn't gain us anything.
      Signed-off-by: default avatarDave Hansen <dave.hansen@linux.intel.com>
      Cc: Andrew Morton <akpm@linux-foundation.org>
      Cc: Andy Lutomirski <luto@kernel.org>
      Cc: Borislav Petkov <bp@alien8.de>
      Cc: Brian Gerst <brgerst@gmail.com>
      Cc: Dave Hansen <dave@sr71.net>
      Cc: Denys Vlasenko <dvlasenk@redhat.com>
      Cc: H. Peter Anvin <hpa@zytor.com>
      Cc: Josh Poimboeuf <jpoimboe@redhat.com>
      Cc: Linus Torvalds <torvalds@linux-foundation.org>
      Cc: Luis R. Rodriguez <mcgrof@suse.com>
      Cc: Peter Zijlstra <peterz@infradead.org>
      Cc: Thomas Gleixner <tglx@linutronix.de>
      Cc: Toshi Kani <toshi.kani@hp.com>
      Cc: dave.hansen@intel.com
      Cc: linux-mm@kvack.org
      Cc: mhocko@suse.com
      Link: http://lkml.kernel.org/r/20160708001911.9A3FD2B6@viggo.jf.intel.com
      Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
  11. 13 Feb, 2015 1 commit
    • Mel Gorman's avatar
      mm: remove remaining references to NUMA hinting bits and helpers · 21d9ee3e
      Mel Gorman authored
      This patch removes the NUMA PTE bits and associated helpers.  As a
      side-effect it increases the maximum possible swap space on x86-64.
      One potential source of problems is races between the marking of PTEs
      PROT_NONE, NUMA hinting faults and migration.  It must be guaranteed that
      a PTE being protected is not faulted in parallel, seen as a pte_none and
      corrupting memory.  The base case is safe but transhuge has problems in
      the past due to an different migration mechanism and a dependance on page
      lock to serialise migrations and warrants a closer look.
      task_work hinting update			parallel fault
      ------------------------			--------------
      						  read? pmd_lock blocks until hinting complete, fail !pmd_none test
      						  write? __do_huge_pmd_anonymous_page acquires pmd_lock, checks pmd_none
      task_work hinting update			parallel migration
      ------------------------			------------------
      						    pmd_lock waits for updates to complete, recheck pmd_same
      Both of those are safe and the case where a transhuge page is inserted
      during a protection update is unchanged.  The case where two processes try
      migrating at the same time is unchanged by this series so should still be
      ok.  I could not find a case where we are accidentally depending on the
      PTE not being cleared and flushed.  If one is missed, it'll manifest as
      corruption problems that start triggering shortly after this series is
      merged and only happen when NUMA balancing is enabled.
      Signed-off-by: default avatarMel Gorman <mgorman@suse.de>
      Tested-by: default avatarSasha Levin <sasha.levin@oracle.com>
      Cc: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
      Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
      Cc: Dave Jones <davej@redhat.com>
      Cc: Hugh Dickins <hughd@google.com>
      Cc: Ingo Molnar <mingo@redhat.com>
      Cc: Kirill Shutemov <kirill.shutemov@linux.intel.com>
      Cc: Linus Torvalds <torvalds@linux-foundation.org>
      Cc: Paul Mackerras <paulus@samba.org>
      Cc: Rik van Riel <riel@redhat.com>
      Cc: Mark Brown <broonie@kernel.org>
      Cc: Stephen Rothwell <sfr@canb.auug.org.au>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
  12. 10 Feb, 2015 1 commit
  13. 16 Sep, 2014 1 commit
    • Yasuaki Ishimatsu's avatar
      x86/mm/hotplug: Modify PGD entry when removing memory · 9661d5bc
      Yasuaki Ishimatsu authored
      When hot-adding/removing memory, sync_global_pgds() is called
      for synchronizing PGD to PGD entries of all processes MM.  But
      when hot-removing memory, sync_global_pgds() does not work
      At first, sync_global_pgds() checks whether target PGD is none
      or not.  And if PGD is none, the PGD is skipped.  But when
      hot-removing memory, PGD may be none since PGD may be cleared by
      free_pud_table().  So when sync_global_pgds() is called after
      hot-removing memory, sync_global_pgds() should not skip PGD even
      if the PGD is none.  And sync_global_pgds() must clear PGD
      entries of all processes MM.
      Currently sync_global_pgds() does not clear PGD entries of all
      processes MM when hot-removing memory.  So when hot adding
      memory which is same memory range as removed memory after
      hot-removing memory, following call traces are shown:
       kernel BUG at arch/x86/mm/init_64.c:206!
       [<ffffffff815e0c80>] kernel_physical_mapping_init+0x1b2/0x1d2
       [<ffffffff815ced94>] init_memory_mapping+0x1d4/0x380
       [<ffffffff8104aebd>] arch_add_memory+0x3d/0xd0
       [<ffffffff815d03d9>] add_memory+0xb9/0x1b0
       [<ffffffff81352415>] acpi_memory_device_add+0x1af/0x28e
       [<ffffffff81325dc4>] acpi_bus_device_attach+0x8c/0xf0
       [<ffffffff813413b9>] acpi_ns_walk_namespace+0xc8/0x17f
       [<ffffffff81325d38>] ? acpi_bus_type_and_status+0xb7/0xb7
       [<ffffffff81325d38>] ? acpi_bus_type_and_status+0xb7/0xb7
       [<ffffffff813418ed>] acpi_walk_namespace+0x95/0xc5
       [<ffffffff81326b4c>] acpi_bus_scan+0x9a/0xc2
       [<ffffffff81326bff>] acpi_scan_bus_device_check+0x8b/0x12e
       [<ffffffff81326cb5>] acpi_scan_device_check+0x13/0x15
       [<ffffffff81320122>] acpi_os_execute_deferred+0x25/0x32
       [<ffffffff8107e02b>] process_one_work+0x17b/0x460
       [<ffffffff8107edfb>] worker_thread+0x11b/0x400
       [<ffffffff8107ece0>] ? rescuer_thread+0x400/0x400
       [<ffffffff81085aef>] kthread+0xcf/0xe0
       [<ffffffff81085a20>] ? kthread_create_on_node+0x140/0x140
       [<ffffffff815fc76c>] ret_from_fork+0x7c/0xb0
       [<ffffffff81085a20>] ? kthread_create_on_node+0x140/0x140
      This patch clears PGD entries of all processes MM when
      sync_global_pgds() is called after hot-removing memory
      Signed-off-by: default avatarYasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>
      Acked-by: default avatarToshi Kani <toshi.kani@hp.com>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Cc: Tang Chen <tangchen@cn.fujitsu.com>
      Cc: Gu Zheng <guz.fnst@cn.fujitsu.com>
      Cc: Zhang Yanfei <zhangyanfei@cn.fujitsu.com>
      Cc: Linus Torvalds <torvalds@linux-foundation.org>
      Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
  14. 10 Sep, 2014 1 commit
    • Stefan Bader's avatar
      x86/xen: don't copy bogus duplicate entries into kernel page tables · 0b5a5063
      Stefan Bader authored
      When RANDOMIZE_BASE (KASLR) is enabled; or the sum of all loaded
      modules exceeds 512 MiB, then loading modules fails with a warning
      (and hence a vmalloc allocation failure) because the PTEs for the
      newly-allocated vmalloc address space are not zero.
        WARNING: CPU: 0 PID: 494 at linux/mm/vmalloc.c:128
      This is caused by xen_setup_kernel_pagetables() copying
      level2_kernel_pgt into level2_fixmap_pgt, overwriting many non-present
      Without KASLR, the normal kernel image size only covers the first half
      of level2_kernel_pgt and module space starts after that.
      L4[511]->level3_kernel_pgt[510]->level2_kernel_pgt[  0..255]->kernel
                                [511]->level2_fixmap_pgt[  0..505]->module
      This allows 512 MiB of of module vmalloc space to be used before
      having to use the corrupted level2_fixmap_pgt entries.
      With KASLR enabled, the kernel image uses the full PUD range of 1G and
      module space starts in the level2_fixmap_pgt. So basically:
      And now no module vmalloc space can be used without using the corrupt
      level2_fixmap_pgt entries.
      Fix this by properly converting the level2_fixmap_pgt entries to MFNs,
      and setting level1_fixmap_pgt as read-only.
      A number of comments were also using the the wrong L3 offset for
      level2_kernel_pgt.  These have been corrected.
      Signed-off-by: default avatarStefan Bader <stefan.bader@canonical.com>
      Signed-off-by: default avatarDavid Vrabel <david.vrabel@citrix.com>
      Reviewed-by: default avatarBoris Ostrovsky <boris.ostrovsky@oracle.com>
      Cc: stable@vger.kernel.org
  15. 04 Jun, 2014 2 commits
    • Cyrill Gorcunov's avatar
      mm: x86 pgtable: drop unneeded preprocessor ifdef · 2373eaec
      Cyrill Gorcunov authored
      _PAGE_BIT_FILE (bit 6) is always less than _PAGE_BIT_PROTNONE (bit 8), so
      drop redundant #ifdef.
      Signed-off-by: default avatarCyrill Gorcunov <gorcunov@openvz.org>
      Cc: Linus Torvalds <torvalds@linux-foundation.org>
      Cc: Mel Gorman <mgorman@suse.de>
      Cc: Peter Anvin <hpa@zytor.com>
      Cc: Ingo Molnar <mingo@kernel.org>
      Cc: Steven Noonan <steven@uplinklabs.net>
      Cc: Rik van Riel <riel@redhat.com>
      Cc: David Vrabel <david.vrabel@citrix.com>
      Cc: Peter Zijlstra <peterz@infradead.org>
      Cc: Pavel Emelyanov <xemul@parallels.com>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    • Mel Gorman's avatar
      x86: define _PAGE_NUMA by reusing software bits on the PMD and PTE levels · c46a7c81
      Mel Gorman authored
      _PAGE_NUMA is currently an alias of _PROT_PROTNONE to trap NUMA hinting
      faults on x86.  Care is taken such that _PAGE_NUMA is used only in
      situations where the VMA flags distinguish between NUMA hinting faults
      and prot_none faults.  This decision was x86-specific and conceptually
      it is difficult requiring special casing to distinguish between PROTNONE
      and NUMA ptes based on context.
      Fundamentally, we only need the _PAGE_NUMA bit to tell the difference
      between an entry that is really unmapped and a page that is protected
      for NUMA hinting faults as if the PTE is not present then a fault will
      be trapped.
      Swap PTEs on x86-64 use the bits after _PAGE_GLOBAL for the offset.
      This patch shrinks the maximum possible swap size and uses the bit to
      uniquely distinguish between NUMA hinting ptes and swap ptes.
      Signed-off-by: default avatarMel Gorman <mgorman@suse.de>
      Cc: David Vrabel <david.vrabel@citrix.com>
      Cc: Ingo Molnar <mingo@kernel.org>
      Cc: Peter Anvin <hpa@zytor.com>
      Cc: Fengguang Wu <fengguang.wu@intel.com>
      Cc: Linus Torvalds <torvalds@linux-foundation.org>
      Cc: Steven Noonan <steven@uplinklabs.net>
      Cc: Rik van Riel <riel@redhat.com>
      Cc: Peter Zijlstra <peterz@infradead.org>
      Cc: Andrea Arcangeli <aarcange@redhat.com>
      Cc: Dave Hansen <dave.hansen@intel.com>
      Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
      Cc: Cyrill Gorcunov <gorcunov@gmail.com>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
  16. 24 Jan, 2013 1 commit
  17. 17 Nov, 2012 1 commit
  18. 09 Oct, 2012 1 commit
    • David Miller's avatar
      mm: Add and use update_mmu_cache_pmd() in transparent huge page code. · b113da65
      David Miller authored
      The transparent huge page code passes a PMD pointer in as the third
      argument of update_mmu_cache(), which expects a PTE pointer.
      This never got noticed because X86 implements update_mmu_cache() as a
      macro and thus we don't get any type checking, and X86 is the only
      architecture which supports transparent huge pages currently.
      Before other architectures can support transparent huge pages properly we
      need to add a new interface which will take a PMD pointer as the third
      argument rather than a PTE pointer.
      [akpm@linux-foundation.org: implement update_mm_cache_pmd() for s390]
      Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
      Cc: Andrea Arcangeli <aarcange@redhat.com>
      Cc: Johannes Weiner <hannes@cmpxchg.org>
      Cc: Gerald Schaefer <gerald.schaefer@de.ibm.com>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
  19. 06 Jun, 2012 1 commit
  20. 14 Jan, 2011 4 commits
    • Johannes Weiner's avatar
      thp: add x86 32bit support · f2d6bfe9
      Johannes Weiner authored
      Add support for transparent hugepages to x86 32bit.
      Share the same VM_ bitflag for VM_MAPPED_COPY.  mm/nommu.c will never
      support transparent hugepages.
      Signed-off-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
      Signed-off-by: default avatarAndrea Arcangeli <aarcange@redhat.com>
      Reviewed-by: default avatarRik van Riel <riel@redhat.com>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    • Andrea Arcangeli's avatar
      thp: transparent hugepage core · 71e3aac0
      Andrea Arcangeli authored
      Lately I've been working to make KVM use hugepages transparently without
      the usual restrictions of hugetlbfs.  Some of the restrictions I'd like to
      see removed:
      1) hugepages have to be swappable or the guest physical memory remains
         locked in RAM and can't be paged out to swap
      2) if a hugepage allocation fails, regular pages should be allocated
         instead and mixed in the same vma without any failure and without
         userland noticing
      3) if some task quits and more hugepages become available in the
         buddy, guest physical memory backed by regular pages should be
         relocated on hugepages automatically in regions under
         madvise(MADV_HUGEPAGE) (ideally event driven by waking up the
         kernel deamon if the order=HPAGE_PMD_SHIFT-PAGE_SHIFT list becomes
         not null)
      4) avoidance of reservation and maximization of use of hugepages whenever
         possible. Reservation (needed to avoid runtime fatal faliures) may be ok for
         1 machine with 1 database with 1 database cache with 1 database cache size
         known at boot time. It's definitely not feasible with a virtualization
         hypervisor usage like RHEV-H that runs an unknown number of virtual machines
         with an unknown size of each virtual machine with an unknown amount of
         pagecache that could be potentially useful in the host for guest not using
         O_DIRECT (aka cache=off).
      hugepages in the virtualization hypervisor (and also in the guest!) are
      much more important than in a regular host not using virtualization,
      becasue with NPT/EPT they decrease the tlb-miss cacheline accesses from 24
      to 19 in case only the hypervisor uses transparent hugepages, and they
      decrease the tlb-miss cacheline accesses from 19 to 15 in case both the
      linux hypervisor and the linux guest both uses this patch (though the
      guest will limit the addition speedup to anonymous regions only for
      now...).  Even more important is that the tlb miss handler is much slower
      on a NPT/EPT guest than for a regular shadow paging or no-virtualization
      scenario.  So maximizing the amount of virtual memory cached by the TLB
      pays off significantly more with NPT/EPT than without (even if there would
      be no significant speedup in the tlb-miss runtime).
      The first (and more tedious) part of this work requires allowing the VM to
      handle anonymous hugepages mixed with regular pages transparently on
      regular anonymous vmas.  This is what this patch tries to achieve in the
      least intrusive possible way.  We want hugepages and hugetlb to be used in
      a way so that all applications can benefit without changes (as usual we
      leverage the KVM virtualization design: by improving the Linux VM at
      large, KVM gets the performance boost too).
      The most important design choice is: always fallback to 4k allocation if
      the hugepage allocation fails!  This is the _very_ opposite of some large
      pagecache patches that failed with -EIO back then if a 64k (or similar)
      allocation failed...
      Second important decision (to reduce the impact of the feature on the
      existing pagetable handling code) is that at any time we can split an
      hugepage into 512 regular pages and it has to be done with an operation
      that can't fail.  This way the reliability of the swapping isn't decreased
      (no need to allocate memory when we are short on memory to swap) and it's
      trivial to plug a split_huge_page* one-liner where needed without
      polluting the VM.  Over time we can teach mprotect, mremap and friends to
      handle pmd_trans_huge natively without calling split_huge_page*.  The fact
      it can't fail isn't just for swap: if split_huge_page would return -ENOMEM
      (instead of the current void) we'd need to rollback the mprotect from the
      middle of it (ideally including undoing the split_vma) which would be a
      big change and in the very wrong direction (it'd likely be simpler not to
      call split_huge_page at all and to teach mprotect and friends to handle
      hugepages instead of rolling them back from the middle).  In short the
      very value of split_huge_page is that it can't fail.
      The collapsing and madvise(MADV_HUGEPAGE) part will remain separated and
      incremental and it'll just be an "harmless" addition later if this initial
      part is agreed upon.  It also should be noted that locking-wise replacing
      regular pages with hugepages is going to be very easy if compared to what
      I'm doing below in split_huge_page, as it will only happen when
      page_count(page) matches page_mapcount(page) if we can take the PG_lock
      and mmap_sem in write mode.  collapse_huge_page will be a "best effort"
      that (unlike split_huge_page) can fail at the minimal sign of trouble and
      we can try again later.  collapse_huge_page will be similar to how KSM
      works and the madvise(MADV_HUGEPAGE) will work similar to
      The default I like is that transparent hugepages are used at page fault
      time.  This can be changed with
      /sys/kernel/mm/transparent_hugepage/enabled.  The control knob can be set
      to three values "always", "madvise", "never" which mean respectively that
      hugepages are always used, or only inside madvise(MADV_HUGEPAGE) regions,
      or never used.  /sys/kernel/mm/transparent_hugepage/defrag instead
      controls if the hugepage allocation should defrag memory aggressively
      "always", only inside "madvise" regions, or "never".
      The pmd_trans_splitting/pmd_trans_huge locking is very solid.  The
      put_page (from get_user_page users that can't use mmu notifier like
      O_DIRECT) that runs against a __split_huge_page_refcount instead was a
      pain to serialize in a way that would result always in a coherent page
      count for both tail and head.  I think my locking solution with a
      compound_lock taken only after the page_first is valid and is still a
      PageHead should be safe but it surely needs review from SMP race point of
      view.  In short there is no current existing way to serialize the O_DIRECT
      final put_page against split_huge_page_refcount so I had to invent a new
      one (O_DIRECT loses knowledge on the mapping status by the time gup_fast
      returns so...).  And I didn't want to impact all gup/gup_fast users for
      now, maybe if we change the gup interface substantially we can avoid this
      locking, I admit I didn't think too much about it because changing the gup
      unpinning interface would be invasive.
      If we ignored O_DIRECT we could stick to the existing compound refcounting
      code, by simply adding a get_user_pages_fast_flags(foll_flags) where KVM
      (and any other mmu notifier user) would call it without FOLL_GET (and if
      FOLL_GET isn't set we'd just BUG_ON if nobody registered itself in the
      current task mmu notifier list yet).  But O_DIRECT is fundamental for
      decent performance of virtualized I/O on fast storage so we can't avoid it
      to solve the race of put_page against split_huge_page_refcount to achieve
      a complete hugepage feature for KVM.
      Swap and oom works fine (well just like with regular pages ;).  MMU
      notifier is handled transparently too, with the exception of the young bit
      on the pmd, that didn't have a range check but I think KVM will be fine
      because the whole point of hugepages is that EPT/NPT will also use a huge
      pmd when they notice gup returns pages with PageCompound set, so they
      won't care of a range and there's just the pmd young bit to check in that
      NOTE: in some cases if the L2 cache is small, this may slowdown and waste
      memory during COWs because 4M of memory are accessed in a single fault
      instead of 8k (the payoff is that after COW the program can run faster).
      So we might want to switch the copy_huge_page (and clear_huge_page too) to
      not temporal stores.  I also extensively researched ways to avoid this
      cache trashing with a full prefault logic that would cow in 8k/16k/32k/64k
      up to 1M (I can send those patches that fully implemented prefault) but I
      concluded they're not worth it and they add an huge additional complexity
      and they remove all tlb benefits until the full hugepage has been faulted
      in, to save a little bit of memory and some cache during app startup, but
      they still don't improve substantially the cache-trashing during startup
      if the prefault happens in >4k chunks.  One reason is that those 4k pte
      entries copied are still mapped on a perfectly cache-colored hugepage, so
      the trashing is the worst one can generate in those copies (cow of 4k page
      copies aren't so well colored so they trashes less, but again this results
      in software running faster after the page fault).  Those prefault patches
      allowed things like a pte where post-cow pages were local 4k regular anon
      pages and the not-yet-cowed pte entries were pointing in the middle of
      some hugepage mapped read-only.  If it doesn't payoff substantially with
      todays hardware it will payoff even less in the future with larger l2
      caches, and the prefault logic would blot the VM a lot.  If one is
      emebdded transparent_hugepage can be disabled during boot with sysfs or
      with the boot commandline parameter transparent_hugepage=0 (or
      transparent_hugepage=2 to restrict hugepages inside madvise regions) that
      will ensure not a single hugepage is allocated at boot time.  It is simple
      enough to just disable transparent hugepage globally and let transparent
      hugepages be allocated selectively by applications in the MADV_HUGEPAGE
      region (both at page fault time, and if enabled with the
      collapse_huge_page too through the kernel daemon).
      This patch supports only hugepages mapped in the pmd, archs that have
      smaller hugepages will not fit in this patch alone.  Also some archs like
      power have certain tlb limits that prevents mixing different page size in
      the same regions so they will not fit in this framework that requires
      "graceful fallback" to basic PAGE_SIZE in case of physical memory
      fragmentation.  hugetlbfs remains a perfect fit for those because its
      software limits happen to match the hardware limits.  hugetlbfs also
      remains a perfect fit for hugepage sizes like 1GByte that cannot be hoped
      to be found not fragmented after a certain system uptime and that would be
      very expensive to defragment with relocation, so requiring reservation.
      hugetlbfs is the "reservation way", the point of transparent hugepages is
      not to have any reservation at all and maximizing the use of cache and
      hugepages at all times automatically.
      Some performance result:
      vmx andrea # LD_PRELOAD=/usr/lib64/libhugetlbfs.so HUGETLB_MORECORE=yes HUGETLB_PATH=/mnt/huge/ ./largep
      memset page fault 1566023
      memset tlb miss 453854
      memset second tlb miss 453321
      random access tlb miss 41635
      random access second tlb miss 41658
      vmx andrea # LD_PRELOAD=/usr/lib64/libhugetlbfs.so HUGETLB_MORECORE=yes HUGETLB_PATH=/mnt/huge/ ./largepages3
      memset page fault 1566471
      memset tlb miss 453375
      memset second tlb miss 453320
      random access tlb miss 41636
      random access second tlb miss 41637
      vmx andrea # ./largepages3
      memset page fault 1566642
      memset tlb miss 453417
      memset second tlb miss 453313
      random access tlb miss 41630
      random access second tlb miss 41647
      vmx andrea # ./largepages3
      memset page fault 1566872
      memset tlb miss 453418
      memset second tlb miss 453315
      random access tlb miss 41618
      random access second tlb miss 41659
      vmx andrea # echo 0 > /proc/sys/vm/transparent_hugepage
      vmx andrea # ./largepages3
      memset page fault 2182476
      memset tlb miss 460305
      memset second tlb miss 460179
      random access tlb miss 44483
      random access second tlb miss 44186
      vmx andrea # ./largepages3
      memset page fault 2182791
      memset tlb miss 460742
      memset second tlb miss 459962
      random access tlb miss 43981
      random access second tlb miss 43988
      #include <stdio.h>
      #include <stdlib.h>
      #include <string.h>
      #include <sys/time.h>
      #define SIZE (3UL*1024*1024*1024)
      int main()
      	char *p = malloc(SIZE), *p2;
      	struct timeval before, after;
      	gettimeofday(&before, NULL);
      	memset(p, 0, SIZE);
      	gettimeofday(&after, NULL);
      	printf("memset page fault %Lu\n",
      	       (after.tv_sec-before.tv_sec)*1000000UL +
      	gettimeofday(&before, NULL);
      	memset(p, 0, SIZE);
      	gettimeofday(&after, NULL);
      	printf("memset tlb miss %Lu\n",
      	       (after.tv_sec-before.tv_sec)*1000000UL +
      	gettimeofday(&before, NULL);
      	memset(p, 0, SIZE);
      	gettimeofday(&after, NULL);
      	printf("memset second tlb miss %Lu\n",
      	       (after.tv_sec-before.tv_sec)*1000000UL +
      	gettimeofday(&before, NULL);
      	for (p2 = p; p2 < p+SIZE; p2 += 4096)
      		*p2 = 0;
      	gettimeofday(&after, NULL);
      	printf("random access tlb miss %Lu\n",
      	       (after.tv_sec-before.tv_sec)*1000000UL +
      	gettimeofday(&before, NULL);
      	for (p2 = p; p2 < p+SIZE; p2 += 4096)
      		*p2 = 0;
      	gettimeofday(&after, NULL);
      	printf("random access second tlb miss %Lu\n",
      	       (after.tv_sec-before.tv_sec)*1000000UL +
      	return 0;
      Signed-off-by: default avatarAndrea Arcangeli <aarcange@redhat.com>
      Acked-by: default avatarRik van Riel <riel@redhat.com>
      Signed-off-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    • Andrea Arcangeli's avatar
      thp: add pmd mangling functions to x86 · db3eb96f
      Andrea Arcangeli authored
      Add needed pmd mangling functions with symmetry with their pte
      counterparts.  pmdp_splitting_flush() is the only new addition on the pmd_
      methods and it's needed to serialize the VM against split_huge_page.  It
      simply atomically sets the splitting bit in a similar way
      pmdp_clear_flush_young atomically clears the accessed bit.
      pmdp_splitting_flush() also has to flush the tlb to make it effective
      against gup_fast, but it wouldn't really require to flush the tlb too.
      Just the tlb flush is the simplest operation we can invoke to serialize
      pmdp_splitting_flush() against gup_fast.
      Signed-off-by: default avatarAndrea Arcangeli <aarcange@redhat.com>
      Acked-by: default avatarRik van Riel <riel@redhat.com>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    • Andrea Arcangeli's avatar
      thp: special pmd_trans_* functions · 5f6e8da7
      Andrea Arcangeli authored
      These returns 0 at compile time when the config option is disabled, to
      allow gcc to eliminate the transparent hugepage function calls at compile
      time without additional #ifdefs (only the export of those functions have
      to be visible to gcc but they won't be required at link time and
      huge_memory.o can be not built at all).
      _PAGE_BIT_UNUSED1 is never used for pmd, only on pte.
      Signed-off-by: default avatarAndrea Arcangeli <aarcange@redhat.com>
      Acked-by: default avatarRik van Riel <riel@redhat.com>
      Acked-by: default avatarMel Gorman <mel@csn.ul.ie>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
  21. 26 Oct, 2010 1 commit
  22. 26 Aug, 2010 1 commit
  23. 10 Aug, 2010 1 commit
  24. 20 Feb, 2010 1 commit
    • Russell King's avatar
      MM: Pass a PTE pointer to update_mmu_cache() rather than the PTE itself · 4b3073e1
      Russell King authored
      On VIVT ARM, when we have multiple shared mappings of the same file
      in the same MM, we need to ensure that we have coherency across all
      copies.  We do this via make_coherent() by making the pages
      This used to work fine, until we allowed highmem with highpte - we
      now have a page table which is mapped as required, and is not available
      for modification via update_mmu_cache().
      Ralf Beache suggested getting rid of the PTE value passed to
        On MIPS update_mmu_cache() calls __update_tlb() which walks pagetables
        to construct a pointer to the pte again.  Passing a pte_t * is much
        more elegant.  Maybe we might even replace the pte argument with the
      Ben Herrenschmidt would also like the pte pointer for PowerPC:
        Passing the ptep in there is exactly what I want.  I want that
        -instead- of the PTE value, because I have issue on some ppc cases,
        for I$/D$ coherency, where set_pte_at() may decide to mask out the
      So, pass in the mapped page table pointer into update_mmu_cache(), and
      remove the PTE value, updating all implementations and call sites to
      Includes a fix from Stephen Rothwell:
        sparc: fix fallout from update_mmu_cache API change
      Signed-off-by: default avatarStephen Rothwell <sfr@canb.auug.org.au>
      Acked-by: default avatarBenjamin Herrenschmidt <benh@kernel.crashing.org>
      Signed-off-by: default avatarRussell King <rmk+kernel@arm.linux.org.uk>
  25. 20 Jun, 2009 1 commit
    • Linus Torvalds's avatar
      x86, 64-bit: Clean up user address masking · 9063c61f
      Linus Torvalds authored
      The discussion about using "access_ok()" in get_user_pages_fast() (see
      commit 7f818906
      : "x86: don't use
      'access_ok()' as a range check in get_user_pages_fast()" for details and
      end result), made us notice that x86-64 was really being very sloppy
      about virtual address checking.
      So be way more careful and straightforward about masking x86-64 virtual
       - All the VIRTUAL_MASK* variants now cover half of the address
         space, it's not like we can use the full mask on a signed
         integer, and the larger mask just invites mistakes when
         applying it to either half of the 48-bit address space.
       - /proc/kcore's kc_offset_to_vaddr() becomes a lot more
         obvious when it transforms a file offset into a
         (kernel-half) virtual address.
       - Unify/simplify the 32-bit and 64-bit USER_DS definition to
         be based on TASK_SIZE_MAX.
      This cleanup and more careful/obvious user virtual address checking also
      uncovered a buglet in the x86-64 implementation of strnlen_user(): it
      would do an "access_ok()" check on the whole potential area, even if the
      string itself was much shorter, and thus return an error even for valid
      strings. Our sloppy checking had hidden this.
      So this fixes 'strnlen_user()' to do this properly, the same way we
      already handled user strings in 'strncpy_from_user()'.  Namely by just
      checking the first byte, and then relying on fault handling for the
      rest.  That always works, since we impose a guard page that cannot be
      mapped at the end of the user space address space (and even if we
      didn't, we'd have the address space hole).
      Acked-by: default avatarIngo Molnar <mingo@elte.hu>
      Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
      Cc: Andrew Morton <akpm@linux-foundation.org>
      Cc: Nick Piggin <npiggin@suse.de>
      Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
      Cc: H. Peter Anvin <hpa@zytor.com>
      Cc: Thomas Gleixner <tglx@linutronix.de>
      Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
  26. 12 Apr, 2009 1 commit
    • Jaswinder Singh Rajput's avatar
      x86: clean up declarations and variables · 2c1b284e
      Jaswinder Singh Rajput authored
      Impact: cleanup, no code changed
       - syscalls.h       update declarations due to unifications
       - irq.c            declare smp_generic_interrupt() before it gets used
       - process.c        declare sys_fork() and sys_vfork() before they get used
       - tsc.c            rename tsc_khz shadowed variable
       - apic/probe_32.c  declare apic_default before it gets used
       - apic/nmi.c       prev_nmi_count should be unsigned
       - apic/io_apic.c   declare smp_irq_move_cleanup_interrupt() before it gets used
       - mm/init.c        declare direct_gbpages and free_initrd_mem before they get used
      Signed-off-by: default avatarJaswinder Singh Rajput <jaswinder@kernel.org>
      Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
  27. 11 Feb, 2009 1 commit
  28. 06 Feb, 2009 8 commits