Re: [PATCH 1/2] KVM: x86: svm: Pass XSAVES to guest if available on host

[Jim Mattson]

On Wed, Sep 25, 2019 at 2:37 PM Sebastian Andrzej Siewior
<bigeasy@xxxxxxxxxxxxx> wrote:
>
> In commit
>    55412b2eda2b7 ("kvm: x86: Add kvm_x86_ops hook that enables XSAVES for guest")
>
> XSAVES was enabled on VMX with a few additional tweaks and was always
> disabled on SVM. Before ZEN XSAVES was not available so it made no
> difference. With Zen it is possible to expose it to the guest if it is
> available on the host.
> I didn't find anything close to VMX's "VM-Execution Controls" and
> exposing this flag based on the CPUID flags cause no harm so far.
>
> Expose the XSAVES flag to the guest if the host supports it.
>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
> ---
>  arch/x86/kvm/svm.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index e0368076a1ef9..3878eb766fa39 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -5992,7 +5992,7 @@ static bool svm_mpx_supported(void)
>
>  static bool svm_xsaves_supported(void)
>  {
> -       return false;
> +       return boot_cpu_has(X86_FEATURE_XSAVES);
>  }
>
>  static bool svm_umip_emulated(void)
> --
> 2.23.0

This is inadequate. Please read the existing thread, "[Patch] KVM:
SVM: Fix svm_xsaves_supported." Aaron Lewis is working on completing
this as we speak.