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KVM: nVMX: allow MBEC with EVMCS

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Extend EVMCS1_SUPPORTED_2NDEXEC to allow MBEC and EVMCS to coexist.
Presenting both EVMCS and MBEC simultaneously causes KVM to filter out
MBEC and not present it as a supported control to the guest, preventing
performance gains from MBEC when Windows HVCI is enabled.

The guest may choose not to use MBEC (e.g., if the admin does not enable
Windows HVCI / Memory Integrity), but if they use traditional nested
virt (Hyper-V, WSL2, etc.), having EVMCS exposed is important for
improving nested guest performance. IOW allowing MBEC and EVMCS to
coexist provides maximum optionality to Windows users without
overcomplicating VM administration.

Signed-off-by: Jon Kohler <jon@nutanix.com>
Message-ID: <20251223054806.1611168-8-jon@nutanix.com>
Tested-by: David Riley <d.riley@proxmox.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Jon Kohler 2026-04-08 11:42:10 -04:00 committed by Paolo Bonzini
parent 606ddbfb4c
commit 55a71224bd
1 changed files with 1 additions and 0 deletions
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1
arch/x86/kvm/vmx/hyperv_evmcs.h
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@ -87,6 +87,7 @@
SECONDARY_EXEC_PT_CONCEAL_VMX | \
SECONDARY_EXEC_BUS_LOCK_DETECTION | \
SECONDARY_EXEC_NOTIFY_VM_EXITING | \
SECONDARY_EXEC_MODE_BASED_EPT_EXEC | \
SECONDARY_EXEC_ENCLS_EXITING)
#define EVMCS1_SUPPORTED_3RDEXEC (0ULL)