linux-kernel - Re: [PATCH v7 03/26] x86/fpu/xstate: Add CET supervisor mode state support

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Message-ID: <c6a62843-efd7-46f5-9b25-6ec7eb70f613@intel.com>
Date:   Mon, 27 Nov 2023 12:06:21 +0800
From:   "Yang, Weijiang" <weijiang.yang@...el.com>
To:     Peter Zijlstra <peterz@...radead.org>
CC:     <seanjc@...gle.com>, <pbonzini@...hat.com>,
        <dave.hansen@...el.com>, <kvm@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <chao.gao@...el.com>,
        <rick.p.edgecombe@...el.com>, <mlevitsk@...hat.com>,
        <john.allen@....com>
Subject: Re: [PATCH v7 03/26] x86/fpu/xstate: Add CET supervisor mode state
 support

On 11/24/2023 5:45 PM, Peter Zijlstra wrote:
> On Fri, Nov 24, 2023 at 12:53:07AM -0500, Yang Weijiang wrote:
>
>> Note, in KVM case, guest CET supervisor state i.e., IA32_PL{0,1,2}_MSRs,
>> are preserved after VM-Exit until host/guest fpstates are swapped, but
>> since host supervisor shadow stack is disabled, the preserved MSRs won't
>> hurt host.
> Just to be clear, with FRED all this changes, right? Then we get more
> VMCS fields for SSS state.

Yes, I think so, KVM needs to properly handle guest SSS state and host FRED states.

Thanks!