Commit 2cf7ea9f authored Oct 03, 2018 by Paolo Bonzini

KVM: VMX: hide flexpriority from guest when disabled at the module level



As of commit 8d860bbe ("kvm: vmx: Basic APIC virtualization controls
have three settings"), KVM will disable VIRTUALIZE_APIC_ACCESSES when
a nested guest writes APIC_BASE MSR and kvm-intel.flexpriority=0,
whereas previously KVM would allow a nested guest to enable
VIRTUALIZE_APIC_ACCESSES so long as it's supported in hardware.  That is,
KVM now advertises VIRTUALIZE_APIC_ACCESSES to a guest but doesn't
(always) allow setting it when kvm-intel.flexpriority=0, and may even
initially allow the control and then clear it when the nested guest
writes APIC_BASE MSR, which is decidedly odd even if it doesn't cause
functional issues.

Hide the control completely when the module parameter is cleared.

reported-by: Sean Christopherson <sean.j.christopherson@intel.com>
Fixes: 8d860bbe ("kvm: vmx: Basic APIC virtualization controls have three settings")
Cc: Jim Mattson <jmattson@google.com>
Cc: stable@vger.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

parent fd6b6d9b

arch/x86/kvm/vmx.c

+5 −1

Original line number	Diff line number	Diff line
		@@ -3589,12 +3589,12 @@ static void nested_vmx_setup_ctls_msrs(struct nested_vmx_msrs *msrs, bool apicv)
		msrs->secondary_ctls_high);
		msrs->secondary_ctls_low = 0;
		msrs->secondary_ctls_high &=
		SECONDARY_EXEC_VIRTUALIZE_APIC_ACCESSES \|
		SECONDARY_EXEC_DESC \|
		SECONDARY_EXEC_VIRTUALIZE_X2APIC_MODE \|
		SECONDARY_EXEC_APIC_REGISTER_VIRT \|
		SECONDARY_EXEC_VIRTUAL_INTR_DELIVERY \|
		SECONDARY_EXEC_WBINVD_EXITING;

		/*
		* We can emulate "VMCS shadowing," even if the hardware
		* doesn't support it.
		@@ -3651,6 +3651,10 @@ static void nested_vmx_setup_ctls_msrs(struct nested_vmx_msrs *msrs, bool apicv)
		msrs->secondary_ctls_high \|=
		SECONDARY_EXEC_UNRESTRICTED_GUEST;

		if (flexpriority_enabled)
		msrs->secondary_ctls_high \|=
		SECONDARY_EXEC_VIRTUALIZE_APIC_ACCESSES;

		/* miscellaneous data */
		rdmsr(MSR_IA32_VMX_MISC,
		msrs->misc_low,

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