linux-kernel - [PATCH 7/9] KVM: nVMX: Stuff vmcs02.TSC_MULTIPLIER early on for nested early checks

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Message-ID: <20250919005955.1366256-8-seanjc@google.com>
Date: Thu, 18 Sep 2025 17:59:53 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Sean Christopherson <seanjc@...gle.com>, Paolo Bonzini <pbonzini@...hat.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH 7/9] KVM: nVMX: Stuff vmcs02.TSC_MULTIPLIER early on for
 nested early checks

If KVM is doing "early" nested VM-Enter consistency checks and TSC scaling
is supported, stuff vmcs02's TSC Multiplier early on to avoid getting a
false positive VM-Fail due to trying to do VM-Enter with TSC_MULTIPLIER=0.
To minimize complexity around L1 vs. L2 TSC, KVM sets the actual TSC
Multiplier rather late during VM-Entry, i.e. may have '0' at the time of
early consistency checks.

If vmcs12 has TSC Scaling enabled, use the multiplier from vmcs12 so that
nested early checks actually check vmcs12 state, otherwise throw in an
arbitrary value of '1' (anything non-zero is legal).

Fixes: d041b5ea9335 ("KVM: nVMX: Enable nested TSC scaling")
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/vmx/nested.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index eb838ebeff0f..e3a94bf6d269 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -2352,6 +2352,13 @@ static void prepare_vmcs02_early_rare(struct vcpu_vmx *vmx,
 		else
 			vmcs_write16(VIRTUAL_PROCESSOR_ID, vmx->vpid);
 	}
+
+	if (kvm_caps.has_tsc_control && nested_early_check) {
+		if (nested_cpu_has2(vmcs12, SECONDARY_EXEC_TSC_SCALING))
+			vmcs_write64(TSC_MULTIPLIER, vmcs12->tsc_multiplier);
+		else
+			vmcs_write64(TSC_MULTIPLIER, 1);
+	}
 }

 static void prepare_vmcs02_early(struct vcpu_vmx *vmx, struct loaded_vmcs *vmcs01,
-- 
2.51.0.470.ga7dc726c21-goog