[PATCH v6 06/12] KVM: x86: Kill off DR6_FIXED_1 to prevent future misuse

[Sean Christopherson]

Now that the only user of DR6_FIXED_1 is kvm_get_dr6_fixed_1(), drop the
hardcoded macro to force all references to fixed-1 bits to use the vCPU-
aware helper.

Opportunistically reword the comment about DR6_ACTIVE_LOW to explain why
treating fixed-1 bits as active-low is correct (barring a *very* egregious
architectural goof).

No functional change intended.

Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
---
 arch/x86/kvm/regs.c |  2 +-
 arch/x86/kvm/regs.h | 10 ++++------
 2 files changed, 5 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kvm/regs.c b/arch/x86/kvm/regs.c
index db43ade8ceb1..0c76cf17e884 100644
--- a/arch/x86/kvm/regs.c
+++ b/arch/x86/kvm/regs.c
@@ -774,7 +774,7 @@ EXPORT_SYMBOL_FOR_KVM_INTERNAL(kvm_update_dr7);
 
 unsigned long kvm_get_dr6_fixed_1(struct kvm_vcpu *vcpu)
 {
-	unsigned long fixed = DR6_FIXED_1;
+	unsigned long fixed = DR6_ACTIVE_LOW & ~DR6_VOLATILE;
 
 	if (!guest_cpu_cap_has(vcpu, X86_FEATURE_RTM))
 		fixed |= DR6_RTM;
diff --git a/arch/x86/kvm/regs.h b/arch/x86/kvm/regs.h
index 3ca5cd8a8d95..97c17b120a57 100644
--- a/arch/x86/kvm/regs.h
+++ b/arch/x86/kvm/regs.h
@@ -38,16 +38,14 @@ static_assert(!(KVM_POSSIBLE_CR0_GUEST_BITS & X86_CR0_PDPTR_BITS));
 #define DR6_BT		(1 << 15)
 #define DR6_RTM		(1 << 16)
 /*
- * DR6_ACTIVE_LOW combines fixed-1 and active-low bits.
- * We can regard all the bits in DR6_FIXED_1 as active_low bits;
- * they will never be 0 for now, but when they are defined
- * in the future it will require no code change.
+ * DR6_ACTIVE_LOW combines fixed-1 and active-low bits (bits that are currently
+ * fixed-1 are guaranteed to have active-low semantics if they are ever used to
+ * support a new feature).
  *
- * DR6_ACTIVE_LOW is also used as the init/reset value for DR6.
+ * Note, DR6_ACTIVE_LOW is also the INIT/RESET value for DR6.
  */
 #define DR6_ACTIVE_LOW	0xffff0ff0
 #define DR6_VOLATILE	0x0001e80f
-#define DR6_FIXED_1	(DR6_ACTIVE_LOW & ~DR6_VOLATILE)
 
 #define DR7_BP_EN_MASK	0x000000ff
 #define DR7_GE		(1 << 9)
-- 
2.56.0.rc1.315.gc6ed9934b7-goog