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SubjectRe: [PATCH v5 6/7] KVM: VMX: Expose PKS to guest
On Wed, Aug 11, 2021, Chenyi Qiang wrote:
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index 739be5da3bca..dbee0d639db3 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -458,7 +458,7 @@ void kvm_set_cpu_caps(void)
> F(AVX512_VPOPCNTDQ) | F(UMIP) | F(AVX512_VBMI2) | F(GFNI) |
> F(VAES) | F(VPCLMULQDQ) | F(AVX512_VNNI) | F(AVX512_BITALG) |
> F(CLDEMOTE) | F(MOVDIRI) | F(MOVDIR64B) | 0 /*WAITPKG*/ |
> - F(SGX_LC) | F(BUS_LOCK_DETECT)
> + F(SGX_LC) | F(BUS_LOCK_DETECT) | 0 /*PKS*/

...

> );
> /* Set LA57 based on hardware capability. */
> if (cpuid_ecx(7) & F(LA57))

...

> @@ -7311,6 +7312,14 @@ static __init void vmx_set_cpu_caps(void)
>
> if (cpu_has_vmx_waitpkg())
> kvm_cpu_cap_check_and_set(X86_FEATURE_WAITPKG);
> +
> + /*
> + * PKS is not yet implemented for shadow paging.
> + * If not support VM_{ENTRY, EXIT}_LOAD_IA32_PKRS,
> + * don't expose the PKS as well.
> + */
> + if (enable_ept && cpu_has_load_ia32_pkrs())
> + kvm_cpu_cap_check_and_set(X86_FEATURE_PKS);

I would rather handle the !TDP case in cpuid.c alongside the PKU. The decision
to not support Protection Keys with legacy shadow paging is an x86 decision, not
a VMX decision.

And VMX's extra restriction on the VMCS support should not bleed into common x86.

Can you also opportunistically update the comment (see below) to explain _why_
OSPKE needs to be enabled in order to advertise PKU?

Thanks!

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 2d70edb0f323..c4ed6881857c 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -439,18 +439,23 @@ void kvm_set_cpu_caps(void)
F(AVX512_VPOPCNTDQ) | F(UMIP) | F(AVX512_VBMI2) | F(GFNI) |
F(VAES) | F(VPCLMULQDQ) | F(AVX512_VNNI) | F(AVX512_BITALG) |
F(CLDEMOTE) | F(MOVDIRI) | F(MOVDIR64B) | 0 /*WAITPKG*/ |
- F(SGX_LC) | F(BUS_LOCK_DETECT)
+ F(SGX_LC) | F(BUS_LOCK_DETECT) | F(PKS)
);
/* Set LA57 based on hardware capability. */
if (cpuid_ecx(7) & F(LA57))
kvm_cpu_cap_set(X86_FEATURE_LA57);

/*
- * PKU not yet implemented for shadow paging and requires OSPKE
- * to be set on the host. Clear it if that is not the case
+ * Protection Keys are not supported for shadow paging. PKU further
+ * requires OSPKE to be set on the host in order to use {RD,WR}PKRU to
+ * save/restore the guests PKRU.
*/
- if (!tdp_enabled || !boot_cpu_has(X86_FEATURE_OSPKE))
+ if (!tdp_enabled) {
kvm_cpu_cap_clear(X86_FEATURE_PKU);
+ kvm_cpu_cap_clear(X86_FEATURE_PKS);
+ } else if (!boot_cpu_has(X86_FEATURE_OSPKE)) {
+ kvm_cpu_cap_clear(X86_FEATURE_PKU);
+ }

kvm_cpu_cap_mask(CPUID_7_EDX,
F(AVX512_4VNNIW) | F(AVX512_4FMAPS) | F(SPEC_CTRL) |

and then vmx.c only needs to handle clearing PKS when the VMCS controls aren't
available.

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