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

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Message-ID: <d9abeb5d-989b-1b38-4551-1ccc50c7f400@intel.com>
Date:   Thu, 16 Jun 2022 23:27:08 +0800
From:   "Yang, Weijiang" <weijiang.yang@...el.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "seanjc@...gle.com" <seanjc@...gle.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Edgecombe, Rick P" <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 6/16/2022 6:59 PM, Peter Zijlstra wrote:
> 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 ?

Hmm, you remind me of reading more specs from AMD... I'll check their HW 
solution

if it's available.