linux-kernel - Re: [PATCH 1/2] KVM: x86: Fixup "Get active PCID only when writing a CR3 value"

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Date:   Tue, 9 Mar 2021 09:26:02 -0800
From:   Sean Christopherson <seanjc@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Tom Lendacky <thomas.lendacky@....com>
Subject: Re: [PATCH 1/2] KVM: x86: Fixup "Get active PCID only when writing a
 CR3 value"

On Mon, Mar 08, 2021, Sean Christopherson wrote:
> From: Sean Christopherson <sean.j.christopherson@...el.com>
> 
> Fix SME and PCID, which got horribly mangled on application.

Gah, the SME changes are supposed to be in "KVM: x86/mmu: Mark the PAE roots as
decrypted for shadow paging", which has not yet been merged.  Stuffing them
here doesn't make things work, but it does break git blame.

I'll send you a v2 with more appropriate fixup, and the PAE changes on top.

> Fixes: a16241ae56fa ("KVM: x86: Get active PCID only when writing a CR3 value")
> Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
>  arch/x86/kvm/svm/svm.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index 7876ddf896b8..271196400495 100644
> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -3907,15 +3907,20 @@ static void svm_load_mmu_pgd(struct kvm_vcpu *vcpu, hpa_t root_hpa,
>  	struct vcpu_svm *svm = to_svm(vcpu);
>  	unsigned long cr3;
>  
> -	cr3 = __sme_set(root_hpa);
>  	if (npt_enabled) {
> -		svm->vmcb->control.nested_cr3 = root_hpa;
> +		svm->vmcb->control.nested_cr3 = __sme_set(root_hpa);
>  		vmcb_mark_dirty(svm->vmcb, VMCB_NPT);
>  
>  		/* Loading L2's CR3 is handled by enter_svm_guest_mode.  */
>  		if (!test_bit(VCPU_EXREG_CR3, (ulong *)&vcpu->arch.regs_avail))
>  			return;
>  		cr3 = vcpu->arch.cr3;
> +	} else if (vcpu->arch.mmu->shadow_root_level >= PT64_ROOT_4LEVEL) {
> +		cr3 = __sme_set(root_hpa) | kvm_get_active_pcid(vcpu);
> +	} else {
> +		/* PCID in the guest should be impossible with a 32-bit MMU. */
> +		WARN_ON_ONCE(kvm_get_active_pcid(vcpu));
> +		cr3 = root_hpa;
>  	}
>  
>  	svm->vmcb->save.cr3 = cr3;
> -- 
> 2.30.1.766.gb4fecdf3b7-goog
>