Messages in this thread Patch in this message | | | From | Xin Li <> | Subject | [PATCH v4 1/5] x86/cpufeature: add the cpu feature bit for LKGS | Date | Wed, 19 Oct 2022 02:50:31 -0700 |
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From: "H. Peter Anvin (Intel)" <hpa@zytor.com>
Add the CPU feature bit for LKGS (Load "Kernel" GS).
LKGS instruction is introduced with Intel FRED (flexible return and event delivery) specificaton https://cdrdv2.intel.com/v1/dl/getContent/678938.
LKGS behaves like the MOV to GS instruction except that it loads the base address into the IA32_KERNEL_GS_BASE MSR instead of the GS segment’s descriptor cache, which is exactly what Linux kernel does to load a user level GS base. Thus, with LKGS, there is no need to SWAPGS away from the kernel GS base.
Signed-off-by: H. Peter Anvin (Intel) <hpa@zytor.com> Signed-off-by: Xin Li <xin3.li@intel.com> ---
Change since V2: * add "" not to show "lkgs" in /proc/cpuinfo (Chang S. Bae). --- arch/x86/include/asm/cpufeatures.h | 1 + tools/arch/x86/include/asm/cpufeatures.h | 1 + 2 files changed, 2 insertions(+)
diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h index b71f4f2ecdd5..3dc1a48c2796 100644 --- a/arch/x86/include/asm/cpufeatures.h +++ b/arch/x86/include/asm/cpufeatures.h @@ -308,6 +308,7 @@ /* Intel-defined CPU features, CPUID level 0x00000007:1 (EAX), word 12 */ #define X86_FEATURE_AVX_VNNI (12*32+ 4) /* AVX VNNI instructions */ #define X86_FEATURE_AVX512_BF16 (12*32+ 5) /* AVX512 BFLOAT16 instructions */ +#define X86_FEATURE_LKGS (12*32+ 18) /* "" Load "kernel" (userspace) gs */ /* AMD-defined CPU features, CPUID level 0x80000008 (EBX), word 13 */ #define X86_FEATURE_CLZERO (13*32+ 0) /* CLZERO instruction */ diff --git a/tools/arch/x86/include/asm/cpufeatures.h b/tools/arch/x86/include/asm/cpufeatures.h index ef4775c6db01..9d45071d1730 100644 --- a/tools/arch/x86/include/asm/cpufeatures.h +++ b/tools/arch/x86/include/asm/cpufeatures.h @@ -308,6 +308,7 @@ /* Intel-defined CPU features, CPUID level 0x00000007:1 (EAX), word 12 */ #define X86_FEATURE_AVX_VNNI (12*32+ 4) /* AVX VNNI instructions */ #define X86_FEATURE_AVX512_BF16 (12*32+ 5) /* AVX512 BFLOAT16 instructions */ +#define X86_FEATURE_LKGS (12*32+ 18) /* "" Load "kernel" (userspace) gs */ /* AMD-defined CPU features, CPUID level 0x80000008 (EBX), word 13 */ #define X86_FEATURE_CLZERO (13*32+ 0) /* CLZERO instruction */ -- 2.34.1
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