linux-kernel - Re: [PULL 09/19] KVM: SEV: Add support to handle Page State Change VMGEXIT

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Message-ID: <20240512020634.6sh6cwfwszzmwknq@amd.com>
Date: Sat, 11 May 2024 21:06:34 -0500
From: Michael Roth <michael.roth@....com>
To: Paolo Bonzini <pbonzini@...hat.com>
CC: <kvm@...r.kernel.org>, <linux-kernel@...r.kernel.org>, Sean Christopherson
	<seanjc@...gle.com>, Brijesh Singh <brijesh.singh@....com>, Ashish Kalra
	<ashish.kalra@....com>
Subject: Re: [PULL 09/19] KVM: SEV: Add support to handle Page State Change
 VMGEXIT

On Fri, May 10, 2024 at 04:10:14PM -0500, Michael Roth wrote:
> SEV-SNP VMs can ask the hypervisor to change the page state in the RMP
> table to be private or shared using the Page State Change NAE event
> as defined in the GHCB specification version 2.
> 
> Forward these requests to userspace as KVM_EXIT_VMGEXITs, similar to how
> it is done for requests that don't use a GHCB page.
> 
> As with the MSR-based page-state changes, use the existing
> KVM_HC_MAP_GPA_RANGE hypercall format to deliver these requests to
> userspace via KVM_EXIT_HYPERCALL.
> 
> Signed-off-by: Michael Roth <michael.roth@....com>
> Co-developed-by: Brijesh Singh <brijesh.singh@....com>
> Signed-off-by: Brijesh Singh <brijesh.singh@....com>
> Signed-off-by: Ashish Kalra <ashish.kalra@....com>
> Message-ID: <20240501085210.2213060-11-michael.roth@....com>
> Co-developed-by: Paolo Bonzini <pbonzini@...hat.com>
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> ---
>  arch/x86/include/asm/sev-common.h |  11 ++
>  arch/x86/kvm/svm/sev.c            | 188 ++++++++++++++++++++++++++++++
>  arch/x86/kvm/svm/svm.h            |   5 +
>  3 files changed, 204 insertions(+)
> 
> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> index 438f2e8b8152..46669431b53d 100644
> --- a/arch/x86/kvm/svm/sev.c
> +++ b/arch/x86/kvm/svm/sev.c
> @@ -3274,6 +3274,10 @@ static int sev_es_validate_vmgexit(struct vcpu_svm *svm)
>  	case SVM_VMGEXIT_HV_FEATURES:
>  	case SVM_VMGEXIT_TERM_REQUEST:
>  		break;
> +	case SVM_VMGEXIT_PSC:
> +		if (!sev_snp_guest(vcpu->kvm) || !kvm_ghcb_sw_scratch_is_valid(svm))
> +			goto vmgexit_err;
> +		break;
>  	default:
>  		reason = GHCB_ERR_INVALID_EVENT;
>  		goto vmgexit_err;
> @@ -3503,6 +3507,183 @@ static int snp_begin_psc_msr(struct vcpu_svm *svm, u64 ghcb_msr)
>  	return 0; /* forward request to userspace */
>  }
>  
> +struct psc_buffer {
> +	struct psc_hdr hdr;
> +	struct psc_entry entries[];
> +} __packed;
> +
> +static int snp_begin_psc(struct vcpu_svm *svm, struct psc_buffer *psc);
> +
> +static void snp_complete_psc(struct vcpu_svm *svm, u64 psc_ret)
> +{
> +	svm->sev_es.psc_inflight = 0;
> +	svm->sev_es.psc_idx = 0;
> +	svm->sev_es.psc_2m = false;
> +	ghcb_set_sw_exit_info_2(svm->sev_es.ghcb, VMGEXIT_PSC_ERROR_GENERIC);

Unfortunately an important local change didn't make its way into the tagged
branch (commit 4b3f0135f759). I've updated the pull tag (tags/kvm-queue-snp)
to point to the updated branch (commit e704293d704d), which contains only
the following additional change:

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index 398266bef2ca..57c2c8025547 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -3560,7 +3560,7 @@ static void snp_complete_psc(struct vcpu_svm *svm, u64 psc_ret)
        svm->sev_es.psc_inflight = 0;
        svm->sev_es.psc_idx = 0;
        svm->sev_es.psc_2m = false;
-       ghcb_set_sw_exit_info_2(svm->sev_es.ghcb, VMGEXIT_PSC_ERROR_GENERIC);
+       ghcb_set_sw_exit_info_2(svm->sev_es.ghcb, psc_ret);
 }

 static void __snp_complete_one_psc(struct vcpu_svm *svm)