linux-kernel - Re: [PATCH 11/15] KVM: VMX: Update vmcs.GUEST

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Message-ID: <0271da9d3a7494d9e7439d4b8d6d9c857c83a45e.camel@redhat.com>
Date:   Wed, 15 Dec 2021 17:47:45 +0200
From:   Maxim Levitsky <mlevitsk@...hat.com>
To:     Lai Jiangshan <jiangshanlai@...il.com>,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     Lai Jiangshan <laijs@...ux.alibaba.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH 11/15] KVM: VMX: Update vmcs.GUEST_CR3 only when the
 guest CR3 is dirty

On Mon, 2021-11-08 at 20:44 +0800, Lai Jiangshan wrote:
> From: Lai Jiangshan <laijs@...ux.alibaba.com>
> 
> When vcpu->arch.cr3 is changed, it is marked dirty, so vmcs.GUEST_CR3
> can be updated only when kvm_register_is_dirty(vcpu, VCPU_EXREG_CR3).
> 
> Signed-off-by: Lai Jiangshan <laijs@...ux.alibaba.com>
> ---
>  arch/x86/kvm/vmx/vmx.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index d94e51e9c08f..38b65b97fb7b 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -3126,9 +3126,9 @@ static void vmx_load_mmu_pgd(struct kvm_vcpu *vcpu, hpa_t root_hpa,
>  
>  		if (!enable_unrestricted_guest && !is_paging(vcpu))
>  			guest_cr3 = to_kvm_vmx(kvm)->ept_identity_map_addr;
> -		else if (test_bit(VCPU_EXREG_CR3, (ulong *)&vcpu->arch.regs_avail))
> +		else if (kvm_register_is_dirty(vcpu, VCPU_EXREG_CR3))
>  			guest_cr3 = vcpu->arch.cr3;
> -		else /* vmcs01.GUEST_CR3 is already up-to-date. */
> +		else /* vmcs.GUEST_CR3 is already up-to-date. */
>  			update_guest_cr3 = false;
>  		vmx_ept_load_pdptrs(vcpu);
>  	} else {


I just bisected this patch to break booting a VM with ept=1 but unrestricted_guest=0
(I needed to re-test unrestricted_guest=0 bug related to SMM, but didn't want
to boot without EPT. With ept=0,the VM boots with this patch applied).

Reverting this patch on top of kvm/queue also works.

Best regards,
	Maxim levitsky