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From: Vitaly Kuznetsov <vkuznets@redhat.com>
To: Sean Christopherson <seanjc@google.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
	Wanpeng Li <wanpengli@tencent.com>,
	Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
	kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
	Reiji Watanabe <reijiw@google.com>
Subject: Re: [PATCH v2 02/10] KVM: x86: Clear KVM's cached guest CR3 at RESET/INIT
Date: Tue, 21 Sep 2021 15:52:29 +0200	[thread overview]
Message-ID: <878rzq9gte.fsf@vitty.brq.redhat.com> (raw)
In-Reply-To: <20210921000303.400537-3-seanjc@google.com>

Sean Christopherson <seanjc@google.com> writes:

> Explicitly zero the guest's CR3 and mark it available+dirty at RESET/INIT.
> Per Intel's SDM and AMD's APM, CR3 is zeroed at both RESET and INIT.  For
> RESET, this is a nop as vcpu is zero-allocated.  For INIT, the bug has
> likely escaped notice because no firmware/kernel puts its page tables root
> at PA=0, let alone relies on INIT to get the desired CR3 for such page
> tables.
>
> Cc: stable@vger.kernel.org
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> ---
>  arch/x86/kvm/x86.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index e77a5bf2d940..2cb38c67ed43 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -10899,6 +10899,9 @@ void kvm_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
>  	kvm_set_rflags(vcpu, X86_EFLAGS_FIXED);
>  	kvm_rip_write(vcpu, 0xfff0);
>  
> +	vcpu->arch.cr3 = 0;
> +	kvm_register_mark_dirty(vcpu, VCPU_EXREG_CR3);

kvm_register_mark_dirty() is redundant here as PATCH1 does

      vcpu->arch.regs_avail = ~0;
      vcpu->arch.regs_dirty = ~0;

just a few lines above. The dependency is, however, implicit and this
patch is marked for stable@ (well, PATCH1 has 8 Fixes: tags so I'd
expect it to get picked by everyone too, especially by robots) and
flipping two bits is cheap.

Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>

> +
>  	/*
>  	 * CR0.CD/NW are set on RESET, preserved on INIT.  Note, some versions
>  	 * of Intel's SDM list CD/NW as being set on INIT, but they contradict

-- 
Vitaly


  reply	other threads:[~2021-09-21 13:52 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-21  0:02 [PATCH v2 00/10] KVM: x86: Clean up RESET "emulation" Sean Christopherson
2021-09-21  0:02 ` [PATCH v2 01/10] KVM: x86: Mark all registers as avail/dirty at vCPU creation Sean Christopherson
2021-09-21 13:40   ` Vitaly Kuznetsov
2021-09-21  0:02 ` [PATCH v2 02/10] KVM: x86: Clear KVM's cached guest CR3 at RESET/INIT Sean Christopherson
2021-09-21 13:52   ` Vitaly Kuznetsov [this message]
2021-09-21 13:55     ` Vitaly Kuznetsov
2021-09-21 17:35   ` Paolo Bonzini
2021-09-21  0:02 ` [PATCH v2 03/10] KVM: x86: Do not mark all registers as avail/dirty during RESET/INIT Sean Christopherson
2021-09-21  0:02 ` [PATCH v2 04/10] KVM: x86: Remove defunct setting of CR0.ET for guests during vCPU create Sean Christopherson
2021-09-21 14:23   ` Vitaly Kuznetsov
2021-09-21  0:02 ` [PATCH v2 05/10] KVM: x86: Remove defunct setting of XCR0 for guest " Sean Christopherson
2021-09-21 14:37   ` Vitaly Kuznetsov
2021-09-21  0:02 ` [PATCH v2 06/10] KVM: x86: Fold fx_init() into kvm_arch_vcpu_create() Sean Christopherson
2021-09-21 14:52   ` Vitaly Kuznetsov
2021-10-06 23:04     ` Sean Christopherson
2021-09-21  0:03 ` [PATCH v2 07/10] KVM: VMX: Drop explicit zeroing of MSR guest values at vCPU creation Sean Christopherson
2021-09-21 15:02   ` Vitaly Kuznetsov
2021-09-21  0:03 ` [PATCH v2 08/10] KVM: VMX: Move RESET emulation to vmx_vcpu_reset() Sean Christopherson
2021-09-21  0:03 ` [PATCH v2 09/10] KVM: SVM: Move RESET emulation to svm_vcpu_reset() Sean Christopherson
2021-09-21  0:03 ` [PATCH v2 10/10] KVM: x86: WARN on non-zero CRs at RESET to detect improper initalization Sean Christopherson
2021-09-21 13:59   ` Vitaly Kuznetsov
2021-09-23 16:23 ` [PATCH v2 00/10] KVM: x86: Clean up RESET "emulation" Paolo Bonzini

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