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

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Message-ID: <6e1e9de9-8def-46c3-a238-c1b4ef52e331@intel.com>
Date:   Wed, 31 May 2023 09:11:26 +0800
From:   "Yang, Weijiang" <weijiang.yang@...el.com>
To:     Chao Gao <chao.gao@...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


On 5/30/2023 8:08 PM, Chao Gao wrote:
>>>> --- 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.

OK, will change this part to align with xcr0 settings. Thanks!