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SubjectRe: [PATCH 10/10] KVM: x86: Suppress userspace access failures on unsupported, "emulated" MSRs
On 4/26/2024 2:14 AM, Sean Christopherson wrote:
> Extend KVM's suppression of userspace MSR access failures to MSRs that KVM
> reports as emulated, but are ultimately unsupported, e.g. if the VMX MSRs
> are emulated by KVM, but are unsupported given the vCPU model.
>
> Suggested-by: Weijiang Yang<weijiang.yang@intel.com>
> Signed-off-by: Sean Christopherson<seanjc@google.com>
> ---
> arch/x86/kvm/x86.c | 11 ++++++++---
> 1 file changed, 8 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 4c91189342ff..14cfa25ef0e7 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -491,7 +491,7 @@ static bool kvm_is_immutable_feature_msr(u32 msr)
> return false;
> }
>
> -static bool kvm_is_msr_to_save(u32 msr_index)
> +static bool kvm_is_advertised_msr(u32 msr_index)
> {
> unsigned int i;
>
> @@ -500,6 +500,11 @@ static bool kvm_is_msr_to_save(u32 msr_index)
> return true;
> }
>
> + for (i = 0; i < num_emulated_msrs; i++) {
> + if (emulated_msrs[i] == msr_index)
> + return true;
> + }
> +
> return false;
> }
>
> @@ -529,11 +534,11 @@ static __always_inline int kvm_do_msr_access(struct kvm_vcpu *vcpu, u32 msr,
>
> /*
> * Userspace is allowed to read MSRs, and write '0' to MSRs, that KVM
> - * reports as to-be-saved, even if an MSR isn't fully supported.
> + * advertises to userspace, even if an MSR isn't fully supported.
> * Simply check that @data is '0', which covers both the write '0' case
> * and all reads (in which case @data is zeroed on failure; see above).
> */
> - if (host_initiated && !*data && kvm_is_msr_to_save(msr))
> + if (host_initiated && !*data && kvm_is_advertised_msr(msr))
> return 0;
>
> if (!ignore_msrs) {

Reviewed-by: Weijiang Yang <weijiang.yang@intel.com>


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