linux-kernel - [PATCH] KVM: nVMX: Always enable TSC scaling for L2 when it was enabled for L1

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Date:   Tue, 12 Jul 2022 15:50:09 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>
Cc:     Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Maxim Levitsky <mlevitsk@...hat.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH] KVM: nVMX: Always enable TSC scaling for L2 when it was enabled for L1

Windows 10/11 guests with Hyper-V role (WSL2) enabled are observed to
hang upon boot or shortly after when a non-default TSC frequency was
set for L1. The issue is observed on a host where TSC scaling is
supported. The problem appears to be that Windows doesn't use TSC
frequency for its guests even when the feature is advertised and KVM
filters SECONDARY_EXEC_TSC_SCALING out when creating L2 controls from
L1's. This leads to L2 running with the default frequency (matching
host's) while L1 is running with an altered one.

Keep SECONDARY_EXEC_TSC_SCALING in secondary exec controls for L2 when
it was set for L1. TSC_MULTIPLIER is already correctly computed and
written by prepare_vmcs02().

Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
---
 arch/x86/kvm/vmx/nested.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 778f82015f03..bfa366938c49 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -2284,7 +2284,6 @@ static void prepare_vmcs02_early(struct vcpu_vmx *vmx, struct loaded_vmcs *vmcs0
 				  SECONDARY_EXEC_VIRTUAL_INTR_DELIVERY |
 				  SECONDARY_EXEC_APIC_REGISTER_VIRT |
 				  SECONDARY_EXEC_ENABLE_VMFUNC |
-				  SECONDARY_EXEC_TSC_SCALING |
 				  SECONDARY_EXEC_DESC);

 		if (nested_cpu_has(vmcs12,
-- 
2.35.3