linux-kernel - [PATCH v3 22/25] KVM: nVMX: Always set required-1 bits of pinbased_ctls to PIN_BASED_ALWAYSON_WITHOUT_TRUE

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Message-Id: <20220708144223.610080-23-vkuznets@redhat.com>
Date:   Fri,  8 Jul 2022 16:42:20 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>
Cc:     Anirudh Rayabharam <anrayabh@...ux.microsoft.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Maxim Levitsky <mlevitsk@...hat.com>,
        linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH v3 22/25] KVM: nVMX: Always set required-1 bits of pinbased_ctls to PIN_BASED_ALWAYSON_WITHOUT_TRUE_MSR

Similar to exit_ctls_low, entry_ctls_low, procbased_ctls_low,
pinbased_ctls_low should be set to PIN_BASED_ALWAYSON_WITHOUT_TRUE_MSR
and not host's MSR_IA32_VMX_PINBASED_CTLS value |=
PIN_BASED_ALWAYSON_WITHOUT_TRUE_MSR.

The commit eabeaaccfca0 ("KVM: nVMX: Clean up and fix pin-based
execution controls") which introduced '|=' doesn't mention anything
about why this is needed, the change seems rather accidental.

Note: normally, required-1 portion of MSR_IA32_VMX_PINBASED_CTLS should
be equal to PIN_BASED_ALWAYSON_WITHOUT_TRUE_MSR so no behavioral change
is expected, however, it is (in theory) possible to observe something
different there when e.g. KVM is running as a nested hypervisor. Hope
this doesn't happen in practice.

Reported-by: Jim Mattson <jmattson@...gle.com>
Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
---
 arch/x86/kvm/vmx/nested.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index dcf3ee645212..09654d5c2144 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -6586,7 +6586,7 @@ void nested_vmx_setup_ctls_msrs(struct nested_vmx_msrs *msrs, u32 ept_caps)
 	rdmsr(MSR_IA32_VMX_PINBASED_CTLS,
 		msrs->pinbased_ctls_low,
 		msrs->pinbased_ctls_high);
-	msrs->pinbased_ctls_low |=
+	msrs->pinbased_ctls_low =
 		PIN_BASED_ALWAYSON_WITHOUT_TRUE_MSR;
 	msrs->pinbased_ctls_high &=
 		PIN_BASED_EXT_INTR_MASK |
-- 
2.35.3