linux-kernel - Re: [PATCH v5 04/19] KVM:x86: Refresh CPUID on write to guest MSR_IA32

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Date:   Thu, 10 Aug 2023 09:12:41 +0800
From:   "Yang, Weijiang" <weijiang.yang@...el.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
CC:     Sean Christopherson <seanjc@...gle.com>, <peterz@...radead.org>,
        <john.allen@....com>, <kvm@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <rick.p.edgecombe@...el.com>,
        <chao.gao@...el.com>, <binbin.wu@...ux.intel.com>,
        Zhang Yi Z <yi.z.zhang@...ux.intel.com>
Subject: Re: [PATCH v5 04/19] KVM:x86: Refresh CPUID on write to guest
 MSR_IA32_XSS

On 8/10/2023 8:01 AM, Paolo Bonzini wrote:
> On Wed, Aug 9, 2023 at 10:56 AM Yang, Weijiang <weijiang.yang@...el.com> wrote:
>>> I'm pretty sure I've advocated for the exact opposite in the past, i.e. argued
>>> that KVM's ABI is to not enforce ordering between KVM_SET_CPUID2 and KVM_SET_MSR.
>>> But this is becoming untenable, juggling the dependencies in KVM is complex and
>>> is going to result in a nasty bug at some point.
>>>
>>> For this series, lets just tighten the rules for XSS, i.e. drop the host_initated
>>> exemption.  And in a parallel/separate series, try to do a wholesale cleanup of
>>> all the cases that essentially allow userspace to do KVM_SET_MSR before KVM_SET_CPUID2.
>> OK, will do it for this series and investigate for other MSRs.
>> Thanks!
> Remember that, while the ordering between KVM_SET_CPUID2 and
> KVM_SET_MSR must be enforced(*), the host_initiated path must allow
> the default (generally 0) value.
Yes, will take it, thanks!
> Paolo
>
> (*) this means that you should check guest_cpuid_has even if
> host_initiated == true.
>