[PATCH v3 2/7] x86/cpu, kvm: Define a scattered Null Selector Clears Base feature bit

Kim Phillips
2022-11-29T23:59:19Z

It's a part of the CPUID 0x80000021 leaf, and this allows us to
group this and other CPUID 0x80000021 EAX feature bits to being
propagated via kvm_set_cpu_caps instead of open-coding them in
__do_cpuid_func().

Also use the feature bit definition in check_null_seg_clears_base()
instead of open-coding it.

Signed-off-by: Kim Phillips <kim.phillips@amd.com>
---
arch/x86/include/asm/cpufeatures.h | 1 +
arch/x86/kernel/cpu/common.c | 3 +--
arch/x86/kernel/cpu/scattered.c | 1 +
3 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
index b16fdcedc2b5..5ddde18c1ae8 100644
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -308,6 +308,7 @@
#define X86_FEATURE_CALL_DEPTH (11*32+19) /* "" Call depth tracking for RSB stuffing */
#define X86_FEATURE_MSR_TSX_CTRL (11*32+20) /* "" MSR IA32_TSX_CTRL (Intel) implemented */
#define X86_FEATURE_NO_NESTED_DATA_BP (11*32+21) /* "" AMD No Nested Data Breakpoints */
+#define X86_FEATURE_NULL_SEL_CLR_BASE (11*32+22) /* "" AMD Null Selector Clears Base */

/* Intel-defined CPU features, CPUID level 0x00000007:1 (EAX), word 12 */
#define X86_FEATURE_AVX_VNNI (12*32+ 4) /* AVX VNNI instructions */
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 73cc546e024d..8d28cd7c9072 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1683,8 +1683,7 @@ void check_null_seg_clears_base(struct cpuinfo_x86 *c)
return;

/* Zen3 CPUs advertise Null Selector Clears Base in CPUID. */
- if (c->extended_cpuid_level >= 0x80000021 &&
- cpuid_eax(0x80000021) & BIT(6))
+ if (cpu_has(c, X86_FEATURE_NULL_SEL_CLR_BASE))
return;

/*
diff --git a/arch/x86/kernel/cpu/scattered.c b/arch/x86/kernel/cpu/scattered.c
index 079e253e1049..d0734cc19d37 100644
--- a/arch/x86/kernel/cpu/scattered.c
+++ b/arch/x86/kernel/cpu/scattered.c
@@ -46,6 +46,7 @@ static const struct cpuid_bit cpuid_bits[] = {
{ X86_FEATURE_PROC_FEEDBACK, CPUID_EDX, 11, 0x80000007, 0 },
{ X86_FEATURE_MBA, CPUID_EBX, 6, 0x80000008, 0 },
{ X86_FEATURE_NO_NESTED_DATA_BP,CPUID_EAX, 0, 0x80000021, 0 },
+ { X86_FEATURE_NULL_SEL_CLR_BASE,CPUID_EAX, 6, 0x80000021, 0 },
{ X86_FEATURE_PERFMON_V2, CPUID_EAX, 0, 0x80000022, 0 },
{ X86_FEATURE_AMD_LBR_V2, CPUID_EAX, 1, 0x80000022, 0 },
{ 0, 0, 0, 0, 0 }
--
2.34.1