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From: Vitaly Kuznetsov <vkuznets@redhat.com>
To: Paolo Bonzini <pbonzini@redhat.com>,
	Sean Christopherson <seanjc@google.com>
Cc: Igor Mammedov <imammedo@redhat.com>,
	kvm@vger.kernel.org, Wanpeng Li <wanpengli@tencent.com>,
	Jim Mattson <jmattson@google.com>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/2] KVM: x86: Forbid KVM_SET_CPUID{,2} after KVM_RUN
Date: Mon, 17 Jan 2022 14:02:31 +0100	[thread overview]
Message-ID: <87zgnuldlk.fsf@redhat.com> (raw)
In-Reply-To: <517e8b95-e336-8796-6657-c0f8d554143a@redhat.com>

Paolo Bonzini <pbonzini@redhat.com> writes:

> On 1/17/22 10:55, Vitaly Kuznetsov wrote:
>> No, honestly I was thinking about something much simpler: instead of
>> forbidding KVM_SET_CPUID{,2} after KVM_RUN completely (what we have now
>> in 5.16), we only forbid to change certain data which we know breaks
>> some assumptions in MMU, from the comment:
>> "
>>           * KVM does not correctly handle changing guest CPUID after KVM_RUN, as
>>           * MAXPHYADDR, GBPAGES support, AMD reserved bit behavior, etc.. aren't
>>           * tracked in kvm_mmu_page_role.  As a result, KVM may miss guest page
>>           * faults due to reusing SPs/SPTEs.
>> "
>> It seems that CPU hotplug path doesn't need to change these so we don't
>> need an opt-in/opt-out, we can just forbid changing certain things for
>> the time being. Alternatively, we can silently ignore such changes but I
>> don't quite like it because it would mask bugs in VMMs.
>
> I think the version that only allows exactly the same CPUID is the best, 
> as it leaves less room for future bugs.
>

Ok, I hear your vote) Will prepare v2.

-- 
Vitaly


      reply	other threads:[~2022-01-17 13:02 UTC|newest]

Thread overview: 36+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-11-22 17:58 [PATCH 0/2] " Vitaly Kuznetsov
2021-11-22 17:58 ` [PATCH 1/2] KVM: selftests: Avoid KVM_SET_CPUID2 after KVM_RUN in hyperv_features test Vitaly Kuznetsov
2021-11-22 17:58 ` [PATCH 2/2] KVM: x86: Forbid KVM_SET_CPUID{,2} after KVM_RUN Vitaly Kuznetsov
2021-11-26 12:20   ` Paolo Bonzini
2021-12-27 17:32     ` Igor Mammedov
2022-01-02 17:31       ` Paolo Bonzini
2022-01-03  8:04         ` Vitaly Kuznetsov
2022-01-03  9:40           ` Igor Mammedov
2022-01-03 12:56             ` Vitaly Kuznetsov
2022-01-05  8:17               ` Igor Mammedov
2022-01-05  9:12                 ` Vitaly Kuznetsov
2022-01-05  9:10               ` Paolo Bonzini
2022-01-05 10:09                 ` Vitaly Kuznetsov
2022-01-07  9:02                   ` Vitaly Kuznetsov
2022-01-07 18:15                     ` Paolo Bonzini
2022-01-11  8:00                       ` Igor Mammedov
2022-01-12 13:58                         ` Vitaly Kuznetsov
2022-01-12 18:39                           ` Paolo Bonzini
2022-01-13  9:27                             ` Vitaly Kuznetsov
2022-01-13 14:28                               ` Maxim Levitsky
2022-01-13 14:36                                 ` Vitaly Kuznetsov
2022-01-13 14:41                                   ` Maxim Levitsky
2022-01-13 14:59                                     ` Vitaly Kuznetsov
2022-01-13 16:26                                       ` Sean Christopherson
2022-01-13 16:30                                         ` Maxim Levitsky
2022-01-13 22:33             ` Sean Christopherson
2022-01-14  8:28               ` Maxim Levitsky
2022-01-14 16:08                 ` Sean Christopherson
2022-01-14  8:55               ` Igor Mammedov
2022-01-14  9:31                 ` Vitaly Kuznetsov
2022-01-14 11:22                   ` Igor Mammedov
2022-01-14 12:25                     ` Vitaly Kuznetsov
2022-01-14 17:00                       ` Sean Christopherson
2022-01-17  9:55                         ` Vitaly Kuznetsov
2022-01-17 11:20                           ` Paolo Bonzini
2022-01-17 13:02                             ` Vitaly Kuznetsov [this message]

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