Re: [PATCH v2 1/6] x86/cpufeature: add cpu feature bit for LKGS
From: Chang S. Bae
Date: Tue Oct 11 2022 - 21:40:47 EST
On 10/10/2022 12:01 PM, Xin Li wrote:
diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
index ef4775c6db01..459fb0c21dd4 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 */
The spec says [1]:
"Execution of LKGS causes an invalid-opcode exception (#UD) if CPL >
0."
Perhaps userspace has no interest in this. Then, we can add "" not to
show "lkgs" in /proc/cpuinfo:
+#define X86_FEATURE_LKGS (12*32+ 18) /* "" Load "kernel"
(userspace) gs */
Thanks,
Chang
[1] https://cdrdv2.intel.com/v1/dl/getContent/678938