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From: Vitaly Kuznetsov <vkuznets@redhat.com>
To: Paolo Bonzini <pbonzini@redhat.com>, Igor Mammedov <imammedo@redhat.com>
Cc: kvm@vger.kernel.org, Sean Christopherson <seanjc@google.com>,
	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, 03 Jan 2022 09:04:29 +0100	[thread overview]
Message-ID: <87mtkdqm7m.fsf@redhat.com> (raw)
In-Reply-To: <61325b2b-dc93-5db2-2d0a-dd0900d947f2@redhat.com>

Paolo Bonzini <pbonzini@redhat.com> writes:

> On 12/27/21 18:32, Igor Mammedov wrote:
>>> Tweaked and queued nevertheless, thanks.
>> it seems this patch breaks VCPU hotplug, in scenario:
>> 
>>    1. hotunplug existing VCPU (QEMU stores VCPU file descriptor in parked cpus list)
>>    2. hotplug it again (unsuspecting QEMU reuses stored file descriptor when recreating VCPU)
>> 
>> RHBZ:https://bugzilla.redhat.com/show_bug.cgi?id=2028337#c11
>> 
>
> The fix here would be (in QEMU) to not call KVM_SET_CPUID2 again. 
> However, we need to work around it in KVM, and allow KVM_SET_CPUID2 if 
> the data passed to the ioctl is the same that was set before.

Are we sure the data is going to be *exactly* the same? In particular,
when using vCPU fds from the parked list, do we keep the same
APIC/x2APIC id when hotplugging? Or can we actually hotplug with a
different id?

-- 
Vitaly


  reply	other threads:[~2022-01-03  8:04 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 [this message]
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

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