Commit 617d34d9 authored by Jeremy Fitzhardinge's avatar Jeremy Fitzhardinge Committed by H. Peter Anvin
Browse files

x86, mm: Hold mm->page_table_lock while doing vmalloc_sync



Take mm->page_table_lock while syncing the vmalloc region.  This prevents
a race with the Xen pagetable pin/unpin code, which expects that the
page_table_lock is already held.  If this race occurs, then Xen can see
an inconsistent page type (a page can either be read/write or a pagetable
page, and pin/unpin converts it between them), which will cause either
the pin or the set_p[gm]d to fail; either will crash the kernel.

vmalloc_sync_all() should be called rarely, so this extra use of
page_table_lock should not interfere with its normal users.

The mm pointer is stashed in the pgd page's index field, as that won't
be otherwise used for pgds.
Reported-by: default avatarIan Campbell <ian.cambell@eu.citrix.com>
Originally-by: default avatarJan Beulich <jbeulich@novell.com>
LKML-Reference: <4CB88A4C.1080305@goop.org>
Signed-off-by: default avatarJeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: default avatarH. Peter Anvin <hpa@linux.intel.com>
parent 44235dcd
......@@ -28,6 +28,8 @@ extern unsigned long empty_zero_page[PAGE_SIZE / sizeof(unsigned long)];
extern spinlock_t pgd_lock;
extern struct list_head pgd_list;
extern struct mm_struct *pgd_page_get_mm(struct page *page);
#ifdef CONFIG_PARAVIRT
#include <asm/paravirt.h>
#else /* !CONFIG_PARAVIRT */
......
......@@ -229,7 +229,16 @@ void vmalloc_sync_all(void)
spin_lock_irqsave(&pgd_lock, flags);
list_for_each_entry(page, &pgd_list, lru) {
if (!vmalloc_sync_one(page_address(page), address))
spinlock_t *pgt_lock;
int ret;
pgt_lock = &pgd_page_get_mm(page)->page_table_lock;
spin_lock(pgt_lock);
ret = vmalloc_sync_one(page_address(page), address);
spin_unlock(pgt_lock);
if (!ret)
break;
}
spin_unlock_irqrestore(&pgd_lock, flags);
......
......@@ -116,12 +116,19 @@ void sync_global_pgds(unsigned long start, unsigned long end)
spin_lock_irqsave(&pgd_lock, flags);
list_for_each_entry(page, &pgd_list, lru) {
pgd_t *pgd;
spinlock_t *pgt_lock;
pgd = (pgd_t *)page_address(page) + pgd_index(address);
pgt_lock = &pgd_page_get_mm(page)->page_table_lock;
spin_lock(pgt_lock);
if (pgd_none(*pgd))
set_pgd(pgd, *pgd_ref);
else
BUG_ON(pgd_page_vaddr(*pgd)
!= pgd_page_vaddr(*pgd_ref));
spin_unlock(pgt_lock);
}
spin_unlock_irqrestore(&pgd_lock, flags);
}
......
......@@ -87,7 +87,19 @@ static inline void pgd_list_del(pgd_t *pgd)
#define UNSHARED_PTRS_PER_PGD \
(SHARED_KERNEL_PMD ? KERNEL_PGD_BOUNDARY : PTRS_PER_PGD)
static void pgd_ctor(pgd_t *pgd)
static void pgd_set_mm(pgd_t *pgd, struct mm_struct *mm)
{
BUILD_BUG_ON(sizeof(virt_to_page(pgd)->index) < sizeof(mm));
virt_to_page(pgd)->index = (pgoff_t)mm;
}
struct mm_struct *pgd_page_get_mm(struct page *page)
{
return (struct mm_struct *)page->index;
}
static void pgd_ctor(struct mm_struct *mm, pgd_t *pgd)
{
/* If the pgd points to a shared pagetable level (either the
ptes in non-PAE, or shared PMD in PAE), then just copy the
......@@ -105,8 +117,10 @@ static void pgd_ctor(pgd_t *pgd)
}
/* list required to sync kernel mapping updates */
if (!SHARED_KERNEL_PMD)
if (!SHARED_KERNEL_PMD) {
pgd_set_mm(pgd, mm);
pgd_list_add(pgd);
}
}
static void pgd_dtor(pgd_t *pgd)
......@@ -272,7 +286,7 @@ pgd_t *pgd_alloc(struct mm_struct *mm)
*/
spin_lock_irqsave(&pgd_lock, flags);
pgd_ctor(pgd);
pgd_ctor(mm, pgd);
pgd_prepopulate_pmd(mm, pgd, pmds);
spin_unlock_irqrestore(&pgd_lock, flags);
......
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