linux-kernel - Re: [PATCH v3 07/21] KVM:x86: Refresh CPUID on write to guest MSR_IA32

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Message-ID: <ZHXnP5bEvxPrDg3m@chao-email>
Date:   Tue, 30 May 2023 20:08:31 +0800
From:   Chao Gao <chao.gao@...el.com>
To:     "Yang, Weijiang" <weijiang.yang@...el.com>
CC:     <seanjc@...gle.com>, <pbonzini@...hat.com>, <kvm@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <peterz@...radead.org>,
        <rppt@...nel.org>, <binbin.wu@...ux.intel.com>,
        <rick.p.edgecombe@...el.com>, <john.allen@....com>,
        Zhang Yi Z <yi.z.zhang@...ux.intel.com>
Subject: Re: [PATCH v3 07/21] KVM:x86: Refresh CPUID on write to guest
 MSR_IA32_XSS

>> > --- a/arch/x86/kvm/x86.c
>> > +++ b/arch/x86/kvm/x86.c
>> > @@ -3776,8 +3776,10 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>> > 		 */
>> > 		if (data & ~kvm_caps.supported_xss)
>> Shouldn't we check against the supported value of _this_ guest? similar to
>> guest_supported_xcr0.
>
>I don't think it requires an extra variable to serve per guest purpose.
>
>For guest XSS settings, now we don't add extra constraints like XCR0, thus

QEMU can impose constraints by configuring guest CPUID.0xd.1 to indicate
certain supervisor state components cannot be managed by XSAVES, even
though KVM supports them. IOW, guests may differ in the supported values
for the IA32_XSS MSR.