On Mon, Feb 26, 2018 at 05:13:00PM -0500, Konrad Rzeszutek Wilk wrote:
> 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 ?
Ah I see you posted them! Sorry for that particular noise.
> >
> > 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
> >
