From 8eb060e10185cfc97ef0200d197ec246ba0f9f8c Mon Sep 17 00:00:00 2001
From: Dao Lu <daolu@rivosinc.com>
Date: Mon, 20 Jun 2022 13:15:25 -0700
Subject: [PATCH] arch/riscv: add Zihintpause support
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Implement support for the ZiHintPause extension.
The PAUSE instruction is a HINT that indicates the current hart’s rate
of instruction retirement should be temporarily reduced or paused.
Reviewed-by: Heiko Stuebner <heiko@sntech.de>
Tested-by: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: Dao Lu <daolu@rivosinc.com>
[Palmer: Some minor merge conflicts.]
Link: https://lore.kernel.org/all/20220620201530.3929352-1-daolu@rivosinc.com/
Link: https://lore.kernel.org/all/20220811053356.17375-1-palmer@rivosinc.com/
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
---
arch/riscv/Makefile | 4 ++++
arch/riscv/include/asm/hwcap.h | 5 +++++
arch/riscv/include/asm/vdso/processor.h | 21 ++++++++++++++++++---
arch/riscv/kernel/cpu.c | 1 +
arch/riscv/kernel/cpufeature.c | 1 +
5 files changed, 29 insertions(+), 3 deletions(-)
diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile
index 42d7ff8730aa6..3fa8ef3368224 100644
--- a/arch/riscv/Makefile
+++ b/arch/riscv/Makefile
@@ -60,6 +60,10 @@ riscv-march-$(toolchain-need-zicsr-zifencei) := $(riscv-march-y)_zicsr_zifencei
toolchain-supports-zicbom := $(call cc-option-yn, -march=$(riscv-march-y)_zicbom)
riscv-march-$(toolchain-supports-zicbom) := $(riscv-march-y)_zicbom
+# Check if the toolchain supports Zihintpause extension
+toolchain-supports-zihintpause := $(call cc-option-yn, -march=$(riscv-march-y)_zihintpause)
+riscv-march-$(toolchain-supports-zihintpause) := $(riscv-march-y)_zihintpause
+
KBUILD_CFLAGS += -march=$(subst fd,,$(riscv-march-y))
KBUILD_AFLAGS += -march=$(riscv-march-y)
diff --git a/arch/riscv/include/asm/hwcap.h b/arch/riscv/include/asm/hwcap.h
index ed4045e70f7a9..3c8a5ca95c725 100644
--- a/arch/riscv/include/asm/hwcap.h
+++ b/arch/riscv/include/asm/hwcap.h
@@ -8,6 +8,7 @@
#ifndef _ASM_RISCV_HWCAP_H
#define _ASM_RISCV_HWCAP_H
+#include <asm/errno.h>
#include <linux/bits.h>
#include <uapi/asm/hwcap.h>
@@ -55,6 +56,7 @@ enum riscv_isa_ext_id {
RISCV_ISA_EXT_SSCOFPMF = RISCV_ISA_EXT_BASE,
RISCV_ISA_EXT_SVPBMT,
RISCV_ISA_EXT_ZICBOM,
+ RISCV_ISA_EXT_ZIHINTPAUSE,
RISCV_ISA_EXT_ID_MAX = RISCV_ISA_EXT_MAX,
};
@@ -65,6 +67,7 @@ enum riscv_isa_ext_id {
*/
enum riscv_isa_ext_key {
RISCV_ISA_EXT_KEY_FPU, /* For 'F' and 'D' */
+ RISCV_ISA_EXT_KEY_ZIHINTPAUSE,
RISCV_ISA_EXT_KEY_MAX,
};
@@ -84,6 +87,8 @@ static __always_inline int riscv_isa_ext2key(int num)
return RISCV_ISA_EXT_KEY_FPU;
case RISCV_ISA_EXT_d:
return RISCV_ISA_EXT_KEY_FPU;
+ case RISCV_ISA_EXT_ZIHINTPAUSE:
+ return RISCV_ISA_EXT_KEY_ZIHINTPAUSE;
default:
return -EINVAL;
}
diff --git a/arch/riscv/include/asm/vdso/processor.h b/arch/riscv/include/asm/vdso/processor.h
index 134388cbaaa1d..1e4f8b4aef79d 100644
--- a/arch/riscv/include/asm/vdso/processor.h
+++ b/arch/riscv/include/asm/vdso/processor.h
@@ -4,15 +4,30 @@
#ifndef __ASSEMBLY__
+#include <linux/jump_label.h>
#include <asm/barrier.h>
+#include <asm/hwcap.h>
static inline void cpu_relax(void)
{
+ if (!static_branch_likely(&riscv_isa_ext_keys[RISCV_ISA_EXT_KEY_ZIHINTPAUSE])) {
#ifdef __riscv_muldiv
- int dummy;
- /* In lieu of a halt instruction, induce a long-latency stall. */
- __asm__ __volatile__ ("div %0, %0, zero" : "=r" (dummy));
+ int dummy;
+ /* In lieu of a halt instruction, induce a long-latency stall. */
+ __asm__ __volatile__ ("div %0, %0, zero" : "=r" (dummy));
#endif
+ } else {
+ /*
+ * Reduce instruction retirement.
+ * This assumes the PC changes.
+ */
+#ifdef __riscv_zihintpause
+ __asm__ __volatile__ ("pause");
+#else
+ /* Encoding of the pause instruction */
+ __asm__ __volatile__ (".4byte 0x100000F");
+#endif
+ }
barrier();
}
diff --git a/arch/riscv/kernel/cpu.c b/arch/riscv/kernel/cpu.c
index 76a2a225e3d99..a77c380703c5c 100644
--- a/arch/riscv/kernel/cpu.c
+++ b/arch/riscv/kernel/cpu.c
@@ -94,6 +94,7 @@ static struct riscv_isa_ext_data isa_ext_arr[] = {
__RISCV_ISA_EXT_DATA(sscofpmf, RISCV_ISA_EXT_SSCOFPMF),
__RISCV_ISA_EXT_DATA(svpbmt, RISCV_ISA_EXT_SVPBMT),
__RISCV_ISA_EXT_DATA(zicbom, RISCV_ISA_EXT_ZICBOM),
+ __RISCV_ISA_EXT_DATA(zihintpause, RISCV_ISA_EXT_ZIHINTPAUSE),
__RISCV_ISA_EXT_DATA("", RISCV_ISA_EXT_MAX),
};
diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
index f914e8da157a8..c233fbc5b873b 100644
--- a/arch/riscv/kernel/cpufeature.c
+++ b/arch/riscv/kernel/cpufeature.c
@@ -202,6 +202,7 @@ void __init riscv_fill_hwcap(void)
SET_ISA_EXT_MAP("sscofpmf", RISCV_ISA_EXT_SSCOFPMF);
SET_ISA_EXT_MAP("svpbmt", RISCV_ISA_EXT_SVPBMT);
SET_ISA_EXT_MAP("zicbom", RISCV_ISA_EXT_ZICBOM);
+ SET_ISA_EXT_MAP("zihintpause", RISCV_ISA_EXT_ZIHINTPAUSE);
}
#undef SET_ISA_EXT_MAP
}
--
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