On Sat, Feb 24, 2018 at 01:52:26AM +0100, Paolo Bonzini wrote:
> Use the new MSR feature framework to expose the ARCH_CAPABILITIES MSR to
> userspace. This way, userspace can access the capabilities even if it
> does not have the permissions to read MSRs.
... That is good but could you expand a bit of why it would want this?
I am 99% sure it is due to the lovely spectre_v2 mitigation but
could you include that in the commit message so that in say a year
folks would know what this is?
Also what branch is this based on? I am not seeing this vmx_get_msr_feature
in kvm/master or kvm/linux-next ?
>
> Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> ---
> arch/x86/kvm/vmx.c | 12 +++++++++++-
> arch/x86/kvm/x86.c | 1 +
> 2 files changed, 12 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 130fca0ea1bf..99689061e11e 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -3228,7 +3228,17 @@ static inline bool vmx_feature_control_msr_valid(struct kvm_vcpu *vcpu,
>
> static int vmx_get_msr_feature(struct kvm_msr_entry *msr)
> {
> - return 1;
> + switch (msr->index) {
> + case MSR_IA32_ARCH_CAPABILITIES:
> + if (!boot_cpu_has(X86_FEATURE_ARCH_CAPABILITIES))
> + return 1;
> + rdmsrl(msr->index, msr->data);
> + break;
> + default:
> + return 1;
> + }
> +
> + return 0;
> }
>
> /*
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 54b4ed55945b..e9a8cc9e3b2b 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -1054,6 +1054,7 @@ bool kvm_rdpmc(struct kvm_vcpu *vcpu)
> * can be used by a hypervisor to validate requested CPU features.
> */
> static u32 msr_based_features[] = {
> + MSR_IA32_ARCH_CAPABILITIES,
> MSR_F10H_DECFG,
> };
>
> --
> 1.8.3.1
>
