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From: Paolo Bonzini <pbonzini@redhat.com>
To: Vitaly Kuznetsov <vkuznets@redhat.com>, kvm@vger.kernel.org
Cc: 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: Fri, 26 Nov 2021 13:20:28 +0100	[thread overview]
Message-ID: <16368a89-99ea-e52c-47b6-bd006933ec1f@redhat.com> (raw)
In-Reply-To: <20211122175818.608220-3-vkuznets@redhat.com>

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.

Paolo


  reply	other threads:[~2021-11-26 12:22 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 [this message]
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

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