linux-kernel - Re: [PATCH v10 13/27] KVM: x86: Refresh CPUID on write to guest MSR_IA32

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Message-ID: <ZdRn+A7g395N2AGx@chao-email>
Date: Tue, 20 Feb 2024 16:51:04 +0800
From: Chao Gao <chao.gao@...el.com>
To: Yang Weijiang <weijiang.yang@...el.com>
CC: <seanjc@...gle.com>, <pbonzini@...hat.com>, <dave.hansen@...el.com>,
	<x86@...nel.org>, <kvm@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<peterz@...radead.org>, <rick.p.edgecombe@...el.com>, <mlevitsk@...hat.com>,
	<john.allen@....com>, Zhang Yi Z <yi.z.zhang@...ux.intel.com>
Subject: Re: [PATCH v10 13/27] KVM: x86: Refresh CPUID on write to guest
 MSR_IA32_XSS

On Sun, Feb 18, 2024 at 11:47:19PM -0800, Yang Weijiang wrote:
>Update CPUID.(EAX=0DH,ECX=1).EBX to reflect current required xstate size
>due to XSS MSR modification.
>CPUID(EAX=0DH,ECX=1).EBX reports the required storage size of all enabled
>xstate features in (XCR0 | IA32_XSS). The CPUID value can be used by guest
>before allocate sufficient xsave buffer.
>
>Note, KVM does not yet support any XSS based features, i.e. supported_xss
>is guaranteed to be zero at this time.
>
>Opportunistically modify XSS write access logic as:
>If XSAVES is not enabled in the guest CPUID, forbid setting IA32_XSS msr
>to anything but 0, even if the write is host initiated.
>
>Suggested-by: Sean Christopherson <seanjc@...gle.com>
>Co-developed-by: Zhang Yi Z <yi.z.zhang@...ux.intel.com>
>Signed-off-by: Zhang Yi Z <yi.z.zhang@...ux.intel.com>
>Signed-off-by: Yang Weijiang <weijiang.yang@...el.com>
>Reviewed-by: Maxim Levitsky <mlevitsk@...hat.com>

Reviewed-by: Chao Gao <chao.gao@...el.com>