linux-kernel - [PATCH] KVM: SNP: Fix LBR Virtualization for SNP guest

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Date: Wed, 5 Jun 2024 11:48:10 +0000
From: Ravi Bangoria <ravi.bangoria@....com>
To: <seanjc@...gle.com>, <pbonzini@...hat.com>, <nikunj.dadhania@....com>,
	<sraithal@....com>
CC: <ravi.bangoria@....com>, <thomas.lendacky@....com>, <tglx@...utronix.de>,
	<mingo@...hat.com>, <bp@...en8.de>, <dave.hansen@...ux.intel.com>,
	<x86@...nel.org>, <hpa@...or.com>, <michael.roth@....com>,
	<pankaj.gupta@....com>, <kvm@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <santosh.shukla@....com>
Subject: [PATCH] KVM: SNP: Fix LBR Virtualization for SNP guest

SEV-ES and thus SNP guest mandates LBR Virtualization to be _always_ ON.
Although commit b7e4be0a224f ("KVM: SEV-ES: Delegate LBR virtualization
to the processor") did the correct change for SEV-ES guests, it missed
the SNP. Fix it.

Reported-by: Srikanth Aithal <sraithal@....com>
Fixes: b7e4be0a224f ("KVM: SEV-ES: Delegate LBR virtualization to the processor")
Signed-off-by: Ravi Bangoria <ravi.bangoria@....com>
---
- SNP support was not present while I prepared the original patches and
  that lead to this confusion. Sorry about that.

 arch/x86/kvm/svm/sev.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index 7d401f8a3001..57291525e084 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -2395,6 +2395,14 @@ static int snp_launch_update_vmsa(struct kvm *kvm, struct kvm_sev_cmd *argp)
 		}
 
 		svm->vcpu.arch.guest_state_protected = true;
+		/*
+		 * SEV-ES (and thus SNP) guest mandates LBR Virtualization to
+		 * be _always_ ON. Enable it only after setting
+		 * guest_state_protected because KVM_SET_MSRS allows dynamic
+		 * toggling of LBRV (for performance reason) on write access to
+		 * MSR_IA32_DEBUGCTLMSR when guest_state_protected is not set.
+		 */
+		svm_enable_lbrv(vcpu);
 	}
 
 	return 0;
-- 
2.45.1