linux-kernel - [PATCH RFC v9 36/51] KVM: SVM: Add support to handle MSR based Page State Change VMGEXIT

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Message-ID: <20230612042559.375660-37-michael.roth@amd.com>
Date:   Sun, 11 Jun 2023 23:25:44 -0500
From:   Michael Roth <michael.roth@....com>
To:     <kvm@...r.kernel.org>
CC:     <linux-coco@...ts.linux.dev>, <linux-mm@...ck.org>,
        <linux-crypto@...r.kernel.org>, <x86@...nel.org>,
        <linux-kernel@...r.kernel.org>, <tglx@...utronix.de>,
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        <ashish.kalra@....com>, <nikunj.dadhania@....com>,
        <liam.merwick@...cle.com>, <zhi.a.wang@...el.com>,
        Brijesh Singh <brijesh.singh@....com>
Subject: [PATCH RFC v9 36/51] KVM: SVM: Add support to handle MSR based Page State Change VMGEXIT

From: Brijesh Singh <brijesh.singh@....com>

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 MSR protocol
as defined in the GHCB specification.

When using gmem, private/shared memory is allocated through separate
pools, and KVM relies on userspace issuing a KVM_SET_MEMORY_ATTRIBUTES
KVM ioctl to tell KVM MMU whether or not a particular GFN should be
backed by private memory or not.

Forward these page state change requests to userspace so that it can
issue the expected KVM ioctls. The KVM MMU will handle updating the RMP
entries when it is ready to map a private page into a guest.

Co-developed-by: Michael Roth <michael.roth@....com>
Signed-off-by: Michael Roth <michael.roth@....com>
Signed-off-by: Brijesh Singh <brijesh.singh@....com>
Signed-off-by: Ashish Kalra <ashish.kalra@....com>
---
 arch/x86/kvm/svm/sev.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index 44fdcf407759..2afc59b86b91 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -3233,6 +3233,15 @@ static void set_ghcb_msr(struct vcpu_svm *svm, u64 value)
 	svm->vmcb->control.ghcb_gpa = value;
 }
 
+static int snp_complete_psc_msr_protocol(struct kvm_vcpu *vcpu)
+{
+	struct vcpu_svm *svm = to_svm(vcpu);
+
+	set_ghcb_msr(svm, vcpu->run->vmgexit.ghcb_msr);
+
+	return 1; /* resume */
+}
+
 static int sev_handle_vmgexit_msr_protocol(struct vcpu_svm *svm)
 {
 	struct vmcb_control_area *control = &svm->vmcb->control;
@@ -3333,6 +3342,13 @@ static int sev_handle_vmgexit_msr_protocol(struct vcpu_svm *svm)
 				  GHCB_MSR_INFO_POS);
 		break;
 	}
+	case GHCB_MSR_PSC_REQ:
+		vcpu->run->exit_reason = KVM_EXIT_VMGEXIT;
+		vcpu->run->vmgexit.ghcb_msr = control->ghcb_gpa;
+		vcpu->arch.complete_userspace_io = snp_complete_psc_msr_protocol;
+
+		ret = -1;
+		break;
 	case GHCB_MSR_TERM_REQ: {
 		u64 reason_set, reason_code;
 
-- 
2.25.1