Re: [Patch 3/6] kvm: svm: Add support for XSAVES on AMD

Jim Mattson
2019-10-09T21:29:29Z

On Wed, Oct 9, 2019 at 12:02 AM Paolo Bonzini <pbonzini@redhat.com> wrote:
>
> On 09/10/19 02:41, Aaron Lewis wrote:
> > - /*
> > - * The only supported bit as of Skylake is bit 8, but
> > - * it is not supported on KVM.
> > - */
> > - if (data != 0)
> > - return 1;
>
> This comment is actually not true anymore; Intel supports PT (bit 8) on
> Cascade Lake, so it could be changed to something like
>
> /*
> * We do support PT (bit 8) if kvm_x86_ops->pt_supported(), but
> * guests will have to configure it using WRMSR rather than
> * XSAVES.
> */
>
> Paolo

Isn't it necessary for the host to set IA32_XSS to a superset of the
guest IA32_XSS for proper host-level context-switching?

arch/x86/kernel/fpu/xstate.c has this comment:

* Note that we do not currently set any bits on IA32_XSS so
* 'XCR0 | IA32_XSS == XCR0' for now.