linux-kernel - Re: [PATCH 1/8] KVM: x86: avoid loading a vCPU after .vm

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Message-ID: <YkOkCwUgMD1SVfaD@google.com>
Date:   Wed, 30 Mar 2022 00:27:55 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Maxim Levitsky <mlevitsk@...hat.com>
Cc:     kvm@...r.kernel.org, Jim Mattson <jmattson@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Borislav Petkov <bp@...en8.de>, Joerg Roedel <joro@...tes.org>,
        Ingo Molnar <mingo@...hat.com>,
        Suravee Suthikulpanit <suravee.suthikulpanit@....com>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        linux-kernel@...r.kernel.org,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>, stable@...r.kernel.org
Subject: Re: [PATCH 1/8] KVM: x86: avoid loading a vCPU after .vm_destroy was
 called

On Tue, Mar 22, 2022, Maxim Levitsky wrote:
> This can cause various unexpected issues, since VM is partially
> destroyed at that point.
> 
> For example when AVIC is enabled, this causes avic_vcpu_load to
> access physical id page entry which is already freed by .vm_destroy.

Hmm, the SEV unbinding of ASIDs should be done after MMU teardown too (which your
patch also does).

> 
> Fixes: 8221c1370056 ("svm: Manage vcpu load/unload when enable AVIC")
> Cc: stable@...r.kernel.org
> 
> Signed-off-by: Maxim Levitsky <mlevitsk@...hat.com>
> ---
>  arch/x86/kvm/x86.c | 10 +++-------
>  1 file changed, 3 insertions(+), 7 deletions(-)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index d3a9ce07a565..ba920e537ddf 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -11759,20 +11759,15 @@ static void kvm_unload_vcpu_mmu(struct kvm_vcpu *vcpu)
>  	vcpu_put(vcpu);
>  }
>  
> -static void kvm_free_vcpus(struct kvm *kvm)
> +static void kvm_unload_vcpu_mmus(struct kvm *kvm)
>  {
>  	unsigned long i;
>  	struct kvm_vcpu *vcpu;
>  
> -	/*
> -	 * Unpin any mmu pages first.
> -	 */
>  	kvm_for_each_vcpu(i, vcpu, kvm) {
>  		kvm_clear_async_pf_completion_queue(vcpu);
>  		kvm_unload_vcpu_mmu(vcpu);
>  	}
> -
> -	kvm_destroy_vcpus(kvm);
>  }
>  
>  void kvm_arch_sync_events(struct kvm *kvm)
> @@ -11878,11 +11873,12 @@ void kvm_arch_destroy_vm(struct kvm *kvm)
>  		__x86_set_memory_region(kvm, TSS_PRIVATE_MEMSLOT, 0, 0);
>  		mutex_unlock(&kvm->slots_lock);
>  	}
> +	kvm_unload_vcpu_mmus(kvm);
>  	static_call_cond(kvm_x86_vm_destroy)(kvm);
>  	kvm_free_msr_filter(srcu_dereference_check(kvm->arch.msr_filter, &kvm->srcu, 1));
>  	kvm_pic_destroy(kvm);
>  	kvm_ioapic_destroy(kvm);
> -	kvm_free_vcpus(kvm);
> +	kvm_destroy_vcpus(kvm);

Rather than split kvm_free_vcpus(), can we instead move the call to svm_vm_destroy()
by adding a second hook, .vm_teardown(), which is needed for TDX?  I.e. keep VMX
where it is by using vm_teardown, but effectively move SVM?

https://lore.kernel.org/all/1fa2d0db387a99352d44247728c5b8ae5f5cab4d.1637799475.git.isaku.yamahata@intel.com

>  	kvfree(rcu_dereference_check(kvm->arch.apic_map, 1));
>  	kfree(srcu_dereference_check(kvm->arch.pmu_event_filter, &kvm->srcu, 1));
>  	kvm_mmu_uninit_vm(kvm);
> -- 
> 2.26.3
>