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x86/cpu, kvm: Move X86_FEATURE_LFENCE_RDTSC to its native leaf

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The LFENCE always serializing feature bit was defined as scattered
LFENCE_RDTSC and its native leaf bit position open-coded for KVM.  Add
it to its newly added CPUID leaf 0x80000021 EAX proper.  With
LFENCE_RDTSC in its proper place, the kernel's set_cpu_cap() will
effectively synthesize the feature for KVM going forward.

Also, DE_CFG[1] doesn't need to be set on such CPUs anymore.

  [ bp: Massage and merge diff from Sean. ]

Signed-off-by: Kim Phillips <kim.phillips@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Acked-by: Sean Christopherson <seanjc@google.com>
Link: https://lore.kernel.org/r/20230124163319.2277355-5-kim.phillips@amd.com
This commit is contained in:
Kim Phillips 2023-01-24 10:33:15 -06:00 committed by Borislav Petkov (AMD)
parent a9dc9ec5a1
commit 84168ae786
3 changed files with 16 additions and 5 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

3
arch/x86/include/asm/cpufeatures.h
View file

@ -97,7 +97,7 @@
#define X86_FEATURE_SYSENTER32 ( 3*32+15) /* "" sysenter in IA32 userspace */ #define X86_FEATURE_SYSENTER32 ( 3*32+15) /* "" sysenter in IA32 userspace */
#define X86_FEATURE_REP_GOOD ( 3*32+16) /* REP microcode works well */ #define X86_FEATURE_REP_GOOD ( 3*32+16) /* REP microcode works well */
#define X86_FEATURE_AMD_LBR_V2 ( 3*32+17) /* AMD Last Branch Record Extension Version 2 */ #define X86_FEATURE_AMD_LBR_V2 ( 3*32+17) /* AMD Last Branch Record Extension Version 2 */
#define X86_FEATURE_LFENCE_RDTSC ( 3*32+18) /* "" LFENCE synchronizes RDTSC */ /* FREE, was #define X86_FEATURE_LFENCE_RDTSC ( 3*32+18) "" LFENCE synchronizes RDTSC */
#define X86_FEATURE_ACC_POWER ( 3*32+19) /* AMD Accumulated Power Mechanism */ #define X86_FEATURE_ACC_POWER ( 3*32+19) /* AMD Accumulated Power Mechanism */
#define X86_FEATURE_NOPL ( 3*32+20) /* The NOPL (0F 1F) instructions */ #define X86_FEATURE_NOPL ( 3*32+20) /* The NOPL (0F 1F) instructions */
#define X86_FEATURE_ALWAYS ( 3*32+21) /* "" Always-present feature */ #define X86_FEATURE_ALWAYS ( 3*32+21) /* "" Always-present feature */
@ -429,6 +429,7 @@
/* AMD-defined Extended Feature 2 EAX, CPUID level 0x80000021 (EAX), word 20 */ /* AMD-defined Extended Feature 2 EAX, CPUID level 0x80000021 (EAX), word 20 */
#define X86_FEATURE_NO_NESTED_DATA_BP (20*32+ 0) /* "" No Nested Data Breakpoints */ #define X86_FEATURE_NO_NESTED_DATA_BP (20*32+ 0) /* "" No Nested Data Breakpoints */
#define X86_FEATURE_LFENCE_RDTSC (20*32+ 2) /* "" LFENCE always serializing / synchronizes RDTSC */
/* /*
* BUG word(s) * BUG word(s)

2
arch/x86/kernel/cpu/amd.c
View file

@ -956,7 +956,7 @@ static void init_amd(struct cpuinfo_x86 *c)
init_amd_cacheinfo(c); init_amd_cacheinfo(c);
if (cpu_has(c, X86_FEATURE_XMM2)) { if (!cpu_has(c, X86_FEATURE_LFENCE_RDTSC) && cpu_has(c, X86_FEATURE_XMM2)) {
/* /*
* Use LFENCE for execution serialization. On families which * Use LFENCE for execution serialization. On families which
* don't have that MSR, LFENCE is already serializing. * don't have that MSR, LFENCE is already serializing.

16
arch/x86/kvm/cpuid.c
View file

@ -742,12 +742,22 @@ void kvm_set_cpu_caps(void)
F(SME_COHERENT)); F(SME_COHERENT));
kvm_cpu_cap_mask(CPUID_8000_0021_EAX, kvm_cpu_cap_mask(CPUID_8000_0021_EAX,
F(NO_NESTED_DATA_BP) | F(NO_NESTED_DATA_BP) | F(LFENCE_RDTSC) | 0 /* SmmPgCfgLock */ |
BIT(2) /* LFENCE Always serializing */ | 0 /* SmmPgCfgLock */ |
BIT(6) /* NULL_SEL_CLR_BASE */ | 0 /* PrefetchCtlMsr */ BIT(6) /* NULL_SEL_CLR_BASE */ | 0 /* PrefetchCtlMsr */
); );
/*
* Synthesize "LFENCE is serializing" into the AMD-defined entry in
* KVM's supported CPUID if the feature is reported as supported by the
* kernel. LFENCE_RDTSC was a Linux-defined synthetic feature long
* before AMD joined the bandwagon, e.g. LFENCE is serializing on most
* CPUs that support SSE2. On CPUs that don't support AMD's leaf,
* kvm_cpu_cap_mask() will unfortunately drop the flag due to ANDing
* the mask with the raw host CPUID, and reporting support in AMD's
* leaf can make it easier for userspace to detect the feature.
*/
if (cpu_feature_enabled(X86_FEATURE_LFENCE_RDTSC)) if (cpu_feature_enabled(X86_FEATURE_LFENCE_RDTSC))
kvm_cpu_caps[CPUID_8000_0021_EAX] |= BIT(2) /* LFENCE Always serializing */; kvm_cpu_cap_set(X86_FEATURE_LFENCE_RDTSC);
if (!static_cpu_has_bug(X86_BUG_NULL_SEG)) if (!static_cpu_has_bug(X86_BUG_NULL_SEG))
kvm_cpu_caps[CPUID_8000_0021_EAX] |= BIT(6) /* NULL_SEL_CLR_BASE */; kvm_cpu_caps[CPUID_8000_0021_EAX] |= BIT(6) /* NULL_SEL_CLR_BASE */;
kvm_cpu_caps[CPUID_8000_0021_EAX] |= BIT(9) /* NO_SMM_CTL_MSR */; kvm_cpu_caps[CPUID_8000_0021_EAX] |= BIT(9) /* NO_SMM_CTL_MSR */;