[PATCH 3/6] KVM: x86: Mark x2APIC DFR reg as non-existent for x2APIC

[Sean Christopherson <seanjc@google.com>]

Mark APIC_DFR as being invalid/non-existent in x2APIC mode instead of
handling it as a one-off check in kvm_x2apic_msr_read().  This will allow
reusing "valid_reg_mask" to generate VMX's interception bitmaps for
x2APIC.  Handling DFR in the common read path may also fix the Hyper-V
PV MSR interface, if that can coexist with x2APIC.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/x86/kvm/lapic.c | 11 ++++-------
 1 file changed, 4 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index bf53e4752f30..c49b13418638 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -1541,7 +1541,6 @@ static int kvm_lapic_reg_read(struct kvm_lapic *apic, u32 offset, int len,
 		APIC_REG_MASK(APIC_TASKPRI) |
 		APIC_REG_MASK(APIC_PROCPRI) |
 		APIC_REG_MASK(APIC_LDR) |
-		APIC_REG_MASK(APIC_DFR) |
 		APIC_REG_MASK(APIC_SPIV) |
 		APIC_REGS_MASK(APIC_ISR, APIC_ISR_NR) |
 		APIC_REGS_MASK(APIC_TMR, APIC_ISR_NR) |
@@ -1562,12 +1561,13 @@ static int kvm_lapic_reg_read(struct kvm_lapic *apic, u32 offset, int len,
 		valid_reg_mask |= APIC_REG_MASK(APIC_LVTCMCI);
 
 	/*
-	 * ARBPRI and ICR2 are not valid in x2APIC mode.  WARN if KVM reads ICR
-	 * in x2APIC mode as it's an 8-byte register in x2APIC and needs to be
-	 * manually handled by the caller.
+	 * ARBPRI, DFR, and ICR2 are not valid in x2APIC mode.  WARN if KVM
+	 * reads ICR in x2APIC mode as it's an 8-byte register in x2APIC and
+	 * needs to be manually handled by the caller.
 	 */
 	if (!apic_x2apic_mode(apic))
 		valid_reg_mask |= APIC_REG_MASK(APIC_ARBPRI) |
+				  APIC_REG_MASK(APIC_DFR) |
 				  APIC_REG_MASK(APIC_ICR2);
 	else
 		WARN_ON_ONCE(offset == APIC_ICR);
@@ -3141,9 +3141,6 @@ int kvm_x2apic_msr_read(struct kvm_vcpu *vcpu, u32 msr, u64 *data)
 	if (!lapic_in_kernel(vcpu) || !apic_x2apic_mode(apic))
 		return 1;
 
-	if (reg == APIC_DFR)
-		return 1;
-
 	return kvm_lapic_msr_read(apic, reg, data);
 }
 
-- 
2.39.0.314.g84b9a713c41-goog