From: Igor Mammedov <imammedo@redhat.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Vitaly Kuznetsov <vkuznets@redhat.com>,
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, 27 Dec 2021 18:32:53 +0100 [thread overview]
Message-ID: <20211227183253.45a03ca2@redhat.com> (raw)
In-Reply-To: <16368a89-99ea-e52c-47b6-bd006933ec1f@redhat.com>
On Fri, 26 Nov 2021 13:20:28 +0100
Paolo Bonzini <pbonzini@redhat.com> wrote:
> On 11/22/21 18:58, Vitaly Kuznetsov wrote:
> > - * 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. Alert userspace, but otherwise
> > - * sweep the problem under the rug.
> > - *
> > - * KVM's horrific CPUID ABI makes the problem all but impossible to
> > - * solve, as correctly handling multiple vCPU models (with respect to
> > - * paging and physical address properties) in a single VM would require
> > - * tracking all relevant CPUID information in kvm_mmu_page_role. That
> > - * is very undesirable as it would double the memory requirements for
> > - * gfn_track (see struct kvm_mmu_page_role comments), and in practice
> > - * no sane VMM mucks with the core vCPU model on the fly.
> > + * Changing guest CPUID after KVM_RUN is forbidden, see the comment in
> > + * kvm_arch_vcpu_ioctl().
> > */
>
> The second part of the comment still applies to kvm_mmu_after_set_cpuid
> more than to kvm_arch_vcpu_ioctl().
>
> > r = -EFAULT;
> > [...]
> > + if (vcpu->arch.last_vmentry_cpu != -1)
> > + goto out;
> > +
> > if (copy_from_user(&cpuid, cpuid_arg, sizeof(cpuid)))
> > goto out;
> > r = kvm_vcpu_ioctl_set_cpuid(vcpu, &cpuid, cpuid_arg->entries);
>
> This should be an EINVAL.
>
> 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
>
> Paolo
>
next prev parent reply other threads:[~2021-12-27 17:33 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-11-22 17:58 [PATCH 0/2] KVM: x86: Forbid KVM_SET_CPUID{,2} after KVM_RUN 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 [this message]
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
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