On Wed, Dec 29, 2021, Yang Zhong wrote:
> From: Jing Liu <jing2.liu@xxxxxxxxx>
>
> Disable read emulation of IA32_XFD_ERR MSR if guest cpuid includes XFD.
> 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.
>
> Suggested-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> Signed-off-by: Jing Liu <jing2.liu@xxxxxxxxx>
> Signed-off-by: Yang Zhong <yang.zhong@xxxxxxxxx>
> ---
> arch/x86/kvm/vmx/vmx.c | 6 ++++++
> arch/x86/kvm/vmx/vmx.h | 2 +-
> 2 files changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 4e51de876085..638665b3e241 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -162,6 +162,7 @@ static u32 vmx_possible_passthrough_msrs[MAX_POSSIBLE_PASSTHROUGH_MSRS] = {
> MSR_FS_BASE,
> MSR_GS_BASE,
> MSR_KERNEL_GS_BASE,
> + MSR_IA32_XFD_ERR,
> #endif
> MSR_IA32_SYSENTER_CS,
> MSR_IA32_SYSENTER_ESP,
> @@ -7228,6 +7229,11 @@ static void vmx_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
> }
> }
>
> + if (boot_cpu_has(X86_FEATURE_XFD))
This should be kvm_cpu_cap_has(), not boot_cpu_has(). If 32-bit kernels don't
suppress XFD in boot_cpu_data, then using boot_cpus_has() is wrong. And even if
XFD is suppressed, using kvm_cpu_cap_has() is still preferable.
> + vmx_set_intercept_for_msr(vcpu, MSR_IA32_XFD_ERR, MSR_TYPE_R,
> + !guest_cpuid_has(vcpu, X86_FEATURE_XFD));
> +
> +
> set_cr4_guest_host_mask(vmx);
>
> vmx_write_encls_bitmap(vcpu, NULL);
> diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
> index 4df2ac24ffc1..bf9d3051cd6c 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 13
> +#define MAX_POSSIBLE_PASSTHROUGH_MSRS 14
> struct {
> DECLARE_BITMAP(read, MAX_POSSIBLE_PASSTHROUGH_MSRS);
> DECLARE_BITMAP(write, MAX_POSSIBLE_PASSTHROUGH_MSRS);
