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

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Date:   Fri, 16 Jun 2023 09:58:56 +0800
From:   "Yang, Weijiang" <weijiang.yang@...el.com>
To:     Sean Christopherson <seanjc@...gle.com>
CC:     Chao Gao <chao.gao@...el.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 6/16/2023 7:45 AM, Sean Christopherson wrote:
> On Wed, May 31, 2023, Weijiang Yang wrote:
>> 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!
> Please write KVM-Unit-Tests to verify KVM correctly handles the various MSRs related
> to CET, e.g. a test_cet_msrs() subtest in msr.c would do nicely.  Hmm, though testing
> the combinations of CPUID bits will require multiple x86/unittests.cfg entries.
> Might be time to split up msr.c into a library and then multiple tests.

Since there's already a CET specific unit test app, do you mind adding 
all CET related stuffs to

the app to make it inclusive? e.g.,  validate constraints between CET 
CPUIDs vs. CET/XSS MSRs?