linux-kernel - Re: [PATCH 16/19] KVM: x86: Enable CET virtualization for VMX and advertise CET to userspace

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Date:   Thu, 16 Jun 2022 12:59:01 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Yang Weijiang <weijiang.yang@...el.com>
Cc:     pbonzini@...hat.com, seanjc@...gle.com, x86@...nel.org,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        rick.p.edgecombe@...el.com,
        Sean Christopherson <sean.j.christopherson@...el.com>
Subject: Re: [PATCH 16/19] KVM: x86: Enable CET virtualization for VMX and
 advertise CET to userspace

On Thu, Jun 16, 2022 at 04:46:40AM -0400, Yang Weijiang wrote:
> Set the feature bits so that CET capabilities can be seen in guest via
> CPUID enumeration. Add CR4.CET bit support in order to allow guest set CET
> master control bit(CR4.CET).
> 
> Disable KVM CET feature if unrestricted_guest is unsupported/disabled as
> KVM does not support emulating CET.
> 
> Don't expose CET feature if dependent CET bits are cleared in host XSS,
> or if XSAVES isn't supported.  Updating the CET features in common x86 is
> a little ugly, but there is no clean solution without risking breakage of
> SVM if SVM hardware ever gains support for CET, e.g. moving everything to
> common x86 would prematurely expose CET on SVM.  The alternative is to
> put all the logic in VMX, but that means rereading host_xss in VMX and
> duplicating the XSAVES check across VMX and SVM.

Doesn't Zen3 already have SHSTK ?