[PATCH v4 22/25] KVM: nVMX: Always set required-1 bits of pinbased_ctls to PIN_BASED_ALWAYSON_WITHOUT_TRUE_MSR

Vitaly Kuznetsov
2022-07-14T09:17:39Z

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@google.com>
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.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