Hi Paolo,
On 12/20/2021 5:08 PM, Paolo Bonzini wrote:
>
> On 12/17/21 16:30, Jing Liu wrote:
> > Also disable read emulation of IA32_XFD_ERR MSR at the same point
> > where r/w emulation of IA32_XFD MSR is disabled. This saves one
> > unnecessary VM-exit in guest #NM handler, given that the MSR is
> > already restored with the guest value before the guest is resumed.
> >
> > Signed-off-by: Jing Liu <jing2.liu@xxxxxxxxx>
>
> Why not do this unconditionally (i.e. in patch 13, with the call to
> vmx_disable_intercept_for_msr in function vmx_create_vcpu)?
>
Thanks for reviewing the patches.
If disable unconditionally in vmx_create_vcpu, it means even guest has
no cpuid, the msr read is passthrough to guest and it can read a value, which
seems strange, though spec doesn't mention the read behaviour w/o cpuid.
How about disabling read interception at vmx_vcpu_after_set_cpuid?
if (boot_cpu_has(X86_FEATURE_XFD) && guest_cpuid_has(vcpu, X86_FEATURE_XFD))
vmx_set_intercept_for_msr(vcpu, MSR_IA32_XFD_ERR, MSR_TYPE_R, false);
Thanks,
Jing
> Thanks,
>
> Paolo
>
> > ---
> > arch/x86/kvm/vmx/vmx.c | 2 ++
> > arch/x86/kvm/vmx/vmx.h | 2 +-
> > 2 files changed, 3 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c index
> > 97a823a3f23f..b66a005f076b 100644
> > --- a/arch/x86/kvm/vmx/vmx.c
> > +++ b/arch/x86/kvm/vmx/vmx.c
> > @@ -163,6 +163,7 @@ static u32
> vmx_possible_passthrough_msrs[MAX_POSSIBLE_PASSTHROUGH_MSRS] = {
> > MSR_GS_BASE,
> > MSR_KERNEL_GS_BASE,
> > MSR_IA32_XFD,
> > + MSR_IA32_XFD_ERR,
> > #endif
> > MSR_IA32_SYSENTER_CS,
> > MSR_IA32_SYSENTER_ESP,
> > @@ -1934,6 +1935,7 @@ static u64 vcpu_supported_debugctl(struct
> kvm_vcpu *vcpu)
> > static void vmx_set_xfd_passthrough(struct kvm_vcpu *vcpu)
> > {
> > vmx_disable_intercept_for_msr(vcpu, MSR_IA32_XFD,
> MSR_TYPE_RW);
> > + vmx_disable_intercept_for_msr(vcpu, MSR_IA32_XFD_ERR,
> MSR_TYPE_R);
> > vcpu->arch.xfd_out_of_sync = true;
> > }
> > #endif
> > diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h index
> > bf9d3051cd6c..0a00242a91e7 100644
> > --- a/arch/x86/kvm/vmx/vmx.h
> > +++ b/arch/x86/kvm/vmx/vmx.h
> > @@ -340,7 +340,7 @@ struct vcpu_vmx {
> > struct lbr_desc lbr_desc;
> >
> > /* Save desired MSR intercept (read: pass-through) state */
> > -#define MAX_POSSIBLE_PASSTHROUGH_MSRS 14
> > +#define MAX_POSSIBLE_PASSTHROUGH_MSRS 15
> > struct {
> > DECLARE_BITMAP(read,
> MAX_POSSIBLE_PASSTHROUGH_MSRS);
> > DECLARE_BITMAP(write,
> MAX_POSSIBLE_PASSTHROUGH_MSRS);
> >
