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SubjectRe: [RFC PATCH v2 02/11] KVM: x86: Advertise CPUID.7.2.EDX and RRSBA_CTRL support
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On 4/14/2023 2:25 PM, Chao Gao wrote:
> From: Zhang Chen <chen.zhang@intel.com>
>
> Add a kvm-only CPUID feature leaf for CPUID.7.2.EDX and RRSBA_CTRL
> as the first feature in the leaf.
>
> RRSBA_CTRL is enumerated by CPUID.7.2.EDX[2]. If supported, RRSBA_DIS_U
> (bit 5) and RRSBA_DIS_S (bit 6) of IA32_SPEC_CTRL MSR can be used to
> disable RRSBA behavior for CPL3 and CPL0/1/2 respectively.
>
> Note that KVM does not intercept guests' IA32_SPEC_CTRL MSR accesses
> after a non-zero is written to the MSR. Therefore, guests can already
> toggle the two bits if the host supports RRSBA_CTRL, and no extra code
> is needed to allow guests to toggle the two bits.
>
> Signed-off-by: Zhang Chen <chen.zhang@intel.com>
> Signed-off-by: Chao Gao <chao.gao@intel.com>
> Tested-by: Jiaan Lu <jiaan.lu@intel.com>
> ---
> arch/x86/kvm/cpuid.c | 22 +++++++++++++++++++---
> arch/x86/kvm/reverse_cpuid.h | 7 +++++++
> 2 files changed, 26 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index 9583a110cf5f..f024c3ac2203 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -685,6 +685,10 @@ void kvm_set_cpu_caps(void)
> SF(SGX1) | SF(SGX2) | SF(SGX_EDECCSSA)
> );
>
> + kvm_cpu_cap_init_kvm_defined(CPUID_7_2_EDX,
> + SF(RRSBA_CTRL)
> + );
> +

Is it slightly better to put the new added one after

    kvm_cpu_cap_init_kvm_defined(CPUID_7_1_EDX, ...

to make it in order?


> kvm_cpu_cap_mask(CPUID_8000_0001_ECX,
> F(LAHF_LM) | F(CMP_LEGACY) | 0 /*SVM*/ | 0 /* ExtApicSpace */ |
> F(CR8_LEGACY) | F(ABM) | F(SSE4A) | F(MISALIGNSSE) |
> @@ -949,13 +953,14 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
> break;
> /* function 7 has additional index. */
> case 7:
> - entry->eax = min(entry->eax, 1u);
> + entry->eax = min(entry->eax, 2u);
> cpuid_entry_override(entry, CPUID_7_0_EBX);
> cpuid_entry_override(entry, CPUID_7_ECX);
> cpuid_entry_override(entry, CPUID_7_EDX);
>
> - /* KVM only supports 0x7.0 and 0x7.1, capped above via min(). */
> - if (entry->eax == 1) {
> + max_idx = entry->eax;
> +
> + if (max_idx >= 1) {
> entry = do_host_cpuid(array, function, 1);
> if (!entry)
> goto out;
> @@ -965,6 +970,17 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
> entry->ebx = 0;
> entry->ecx = 0;
> }
> +
> + if (max_idx >= 2) {
> + entry = do_host_cpuid(array, function, 2);
> + if (!entry)
> + goto out;
> +
> + cpuid_entry_override(entry, CPUID_7_2_EDX);
> + entry->eax = 0;
> + entry->ebx = 0;
> + entry->ecx = 0;
> + }
> break;
> case 0xa: { /* Architectural Performance Monitoring */
> union cpuid10_eax eax;
> diff --git a/arch/x86/kvm/reverse_cpuid.h b/arch/x86/kvm/reverse_cpuid.h
> index a5717282bb9c..72bad8314a9c 100644
> --- a/arch/x86/kvm/reverse_cpuid.h
> +++ b/arch/x86/kvm/reverse_cpuid.h
> @@ -15,6 +15,7 @@ enum kvm_only_cpuid_leafs {
> CPUID_12_EAX = NCAPINTS,
> CPUID_7_1_EDX,
> CPUID_8000_0007_EDX,
> + CPUID_7_2_EDX,
> NR_KVM_CPU_CAPS,
>
> NKVMCAPINTS = NR_KVM_CPU_CAPS - NCAPINTS,
> @@ -47,6 +48,9 @@ enum kvm_only_cpuid_leafs {
> /* CPUID level 0x80000007 (EDX). */
> #define KVM_X86_FEATURE_CONSTANT_TSC KVM_X86_FEATURE(CPUID_8000_0007_EDX, 8)
>
> +/* Intel-defined sub-features, CPUID level 0x00000007:2 (EDX) */
> +#define KVM_X86_FEATURE_RRSBA_CTRL KVM_X86_FEATURE(CPUID_7_2_EDX, 2)
> +
> struct cpuid_reg {
> u32 function;
> u32 index;
> @@ -69,6 +73,7 @@ static const struct cpuid_reg reverse_cpuid[] = {
> [CPUID_8000_0007_EBX] = {0x80000007, 0, CPUID_EBX},
> [CPUID_7_EDX] = { 7, 0, CPUID_EDX},
> [CPUID_7_1_EAX] = { 7, 1, CPUID_EAX},
> + [CPUID_7_2_EDX] = { 7, 2, CPUID_EDX},
> [CPUID_12_EAX] = {0x00000012, 0, CPUID_EAX},
> [CPUID_8000_001F_EAX] = {0x8000001f, 0, CPUID_EAX},
> [CPUID_7_1_EDX] = { 7, 1, CPUID_EDX},
> @@ -108,6 +113,8 @@ static __always_inline u32 __feature_translate(int x86_feature)
> return KVM_X86_FEATURE_SGX_EDECCSSA;
> else if (x86_feature == X86_FEATURE_CONSTANT_TSC)
> return KVM_X86_FEATURE_CONSTANT_TSC;
> + else if (x86_feature == X86_FEATURE_RRSBA_CTRL)
> + return KVM_X86_FEATURE_RRSBA_CTRL;
>
> return x86_feature;
> }

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