linux-kernel - Re: [PATCH Part2 RFC v4 39/40] KVM: SVM: Use a VMSA physical address variable for populating VMCB

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Message-ID: <YPdoTK9V3anPZe7C@google.com>
Date:   Wed, 21 Jul 2021 00:20:28 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Brijesh Singh <brijesh.singh@....com>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        linux-efi@...r.kernel.org, platform-driver-x86@...r.kernel.org,
        linux-coco@...ts.linux.dev, linux-mm@...ck.org,
        linux-crypto@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Joerg Roedel <jroedel@...e.de>,
        Tom Lendacky <thomas.lendacky@....com>,
        "H. Peter Anvin" <hpa@...or.com>, Ard Biesheuvel <ardb@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Sergio Lopez <slp@...hat.com>, Peter Gonda <pgonda@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        David Rientjes <rientjes@...gle.com>,
        Dov Murik <dovmurik@...ux.ibm.com>,
        Tobin Feldman-Fitzthum <tobin@....com>,
        Borislav Petkov <bp@...en8.de>,
        Michael Roth <michael.roth@....com>,
        Vlastimil Babka <vbabka@...e.cz>, tony.luck@...el.com,
        npmccallum@...hat.com, brijesh.ksingh@...il.com
Subject: Re: [PATCH Part2 RFC v4 39/40] KVM: SVM: Use a VMSA physical address
 variable for populating VMCB

On Wed, Jul 07, 2021, Brijesh Singh wrote:
> From: Tom Lendacky <thomas.lendacky@....com>
> 
> In preparation to support SEV-SNP AP Creation, use a variable that holds
> the VMSA physical address rather than converting the virtual address.
> This will allow SEV-SNP AP Creation to set the new physical address that
> will be used should the vCPU reset path be taken.

I'm pretty sure adding vmsa_pa is unnecessary.  The next patch sets svm->vmsa_pa
and vmcb->control.vmsa_pa as a pair.  And for the existing code, my proposed
patch to emulate INIT on shutdown would eliminate the one path that zeros the
VMCB[1].  That series patch also drops the init_vmcb() in svm_create_vcpu()[2].

Assuming there are no VMCB shenanigans I'm missing, sev_es_init_vmcb() can do

	if (!init_event)
		svm->vmcb->control.vmsa_pa = __pa(svm->vmsa);

And while I'm thinking of it, the next patch should ideally free svm->vmsa when
the the guest configures a new VMSA for the vCPU.

[1] https://lkml.kernel.org/r/20210713163324.627647-45-seanjc@google.com
[2] https://lkml.kernel.org/r/20210713163324.627647-10-seanjc@google.com

> Signed-off-by: Tom Lendacky <thomas.lendacky@....com>
> Signed-off-by: Brijesh Singh <brijesh.singh@....com>
> ---
>  arch/x86/kvm/svm/sev.c | 5 ++---
>  arch/x86/kvm/svm/svm.c | 9 ++++++++-
>  arch/x86/kvm/svm/svm.h | 1 +
>  3 files changed, 11 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> index 4cb4c1d7e444..d8ad6dd58c87 100644
> --- a/arch/x86/kvm/svm/sev.c
> +++ b/arch/x86/kvm/svm/sev.c
> @@ -3553,10 +3553,9 @@ void sev_es_init_vmcb(struct vcpu_svm *svm)
>  
>  	/*
>  	 * An SEV-ES guest requires a VMSA area that is a separate from the
> -	 * VMCB page. Do not include the encryption mask on the VMSA physical
> -	 * address since hardware will access it using the guest key.
> +	 * VMCB page.
>  	 */
> -	svm->vmcb->control.vmsa_pa = __pa(svm->vmsa);
> +	svm->vmcb->control.vmsa_pa = svm->vmsa_pa;
>  
>  	/* Can't intercept CR register access, HV can't modify CR registers */
>  	svm_clr_intercept(svm, INTERCEPT_CR0_READ);
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index 32e35d396508..74bc635c9608 100644
> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -1379,9 +1379,16 @@ static int svm_create_vcpu(struct kvm_vcpu *vcpu)
>  	svm->vmcb01.ptr = page_address(vmcb01_page);
>  	svm->vmcb01.pa = __sme_set(page_to_pfn(vmcb01_page) << PAGE_SHIFT);
>  
> -	if (vmsa_page)
> +	if (vmsa_page) {
>  		svm->vmsa = page_address(vmsa_page);
>  
> +		/*
> +		 * Do not include the encryption mask on the VMSA physical
> +		 * address since hardware will access it using the guest key.
> +		 */
> +		svm->vmsa_pa = __pa(svm->vmsa);
> +	}
> +
>  	svm->guest_state_loaded = false;
>  
>  	svm_switch_vmcb(svm, &svm->vmcb01);
> diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
> index 9fcfc0a51737..285d9b97b4d2 100644
> --- a/arch/x86/kvm/svm/svm.h
> +++ b/arch/x86/kvm/svm/svm.h
> @@ -177,6 +177,7 @@ struct vcpu_svm {
>  
>  	/* SEV-ES support */
>  	struct sev_es_save_area *vmsa;
> +	hpa_t vmsa_pa;
>  	struct ghcb *ghcb;
>  	struct kvm_host_map ghcb_map;
>  	bool received_first_sipi;
> -- 
> 2.17.1
>