Re: [PATCH v2 11/15] KVM: x86: Add XSAVE Support for Architectural LBR

Yang, Weijiang
2023-01-30T13:13:33Z

On 1/28/2023 6:07 AM, Sean Christopherson wrote:
> On Thu, Nov 24, 2022, Yang Weijiang wrote:
>> From: Like Xu <like.xu@linux.intel.com>
>>
>> On processors supporting XSAVES and XRSTORS, Architectural LBR XSAVE
>> support is enumerated from CPUID.(EAX=0DH, ECX=1):ECX[bit 15].
>> The detailed sub-leaf for Arch LBR is enumerated in CPUID.(0DH, 0FH).
>>
>> XSAVES provides a faster means than RDMSR for guest to read all LBRs.
>> When guest IA32_XSS[bit 15] is set, the Arch LBR state can be saved using
>> XSAVES and restored by XRSTORS with the appropriate RFBM.
>>
>> Signed-off-by: Like Xu <like.xu@linux.intel.com>
>> Signed-off-by: Yang Weijiang <weijiang.yang@intel.com>
>> ---
>> arch/x86/kvm/vmx/vmx.c | 4 ++++
>> arch/x86/kvm/x86.c | 2 +-
>> 2 files changed, 5 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
>> index 359da38a19a1..3bc892e8cf7a 100644
>> --- a/arch/x86/kvm/vmx/vmx.c
>> +++ b/arch/x86/kvm/vmx/vmx.c
>> @@ -7733,6 +7733,10 @@ static __init void vmx_set_cpu_caps(void)
>> kvm_cpu_cap_check_and_set(X86_FEATURE_DS);
>> kvm_cpu_cap_check_and_set(X86_FEATURE_DTES64);
>> }
>> + if (!cpu_has_vmx_arch_lbr()) {
>> + kvm_cpu_cap_clear(X86_FEATURE_ARCH_LBR);
> No, this needs to be opt-in, not opt-out. I.e. omit the flag from common CPUID
> code and set it if and only if it's fully supported. It's not out of the realm
> of possibilities that AMD might want to support arch LBRs, at which point those
> CPUs would explode.

Will modify this patch.

>
>> + kvm_caps.supported_xss &= ~XFEATURE_MASK_LBR;
>> + }
>>
>> if (!enable_pmu)
>> kvm_cpu_cap_clear(X86_FEATURE_PDCM);
>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>> index 889be0c9176d..38df08d9d0cb 100644
>> --- a/arch/x86/kvm/x86.c
>> +++ b/arch/x86/kvm/x86.c
>> @@ -217,7 +217,7 @@ static struct kvm_user_return_msrs __percpu *user_return_msrs;
>> | XFEATURE_MASK_BNDCSR | XFEATURE_MASK_AVX512 \
>> | XFEATURE_MASK_PKRU | XFEATURE_MASK_XTILE)
>>
>> -#define KVM_SUPPORTED_XSS 0
>> +#define KVM_SUPPORTED_XSS XFEATURE_MASK_LBR
>>
>> u64 __read_mostly host_efer;
>> EXPORT_SYMBOL_GPL(host_efer);
>> --
>> 2.27.0
>>