KVM: x86: Mark x2APIC DFR reg as non-existent for x2APIC

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.

Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Link: https://lore.kernel.org/r/20230107011025.565472-4-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 814b6510605744088600ea5eae91c3849b45d2d7..91e6f958d4b2fee6cb82635560b5b9b05ad5be0a 100644 (file)
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -1573,7 +1573,6 @@ 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) |
@@ -1594,12 +1593,13 @@ 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);
@@ -3147,9 +3147,6 @@ 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);
 }