[PATCH v4 27/30] KVM: x86: Rework kvm_arch_interrupt_allowed() into kvm_is_interrupt_allowed()

[Sean Christopherson <seanjc@google.com>]

Rename kvm_arch_interrupt_allowed() to kvm_is_interrupt_allowed() and
change its return type to a boolean, as the purpose of the helper is purely
to check if interrupts are architecturally allowed.  I.e. whether or not
interrupts are temporarily disallowed due a pending nested VM-Enter is
irrelevant (and callers are most definitely not supposed to care).

Opportunistically bury the helper in x86.c, as it hasn't been referenced by
arch-neutral code since commit a1b37100d9e2 ("KVM: Reduce runnability
interface with arch support code"), and has long since gained _very_
x86-specific semantics (see above).

Opportunistically add a comment to call out that treating -EBUSY as
"allowed" is intentional.

For all intents and purposes, no functional change intended (KVM treats
-EBUSY as "allowed" before and after).

Cc: Yosry Ahmed <yosry@kernel.org>
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/x86/include/asm/kvm_host.h |  1 -
 arch/x86/kvm/x86.c              | 23 +++++++++++++++--------
 2 files changed, 15 insertions(+), 9 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 0f6f71642e1d..878944aaea85 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -2338,7 +2338,6 @@ enum {
 # define kvm_memslots_for_spte_role(kvm, role) __kvm_memslots(kvm, 0)
 #endif
 
-int kvm_arch_interrupt_allowed(struct kvm_vcpu *vcpu);
 void kvm_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event);
 
 u64 kvm_scale_tsc(u64 tsc, u64 ratio);
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index e0456133133b..ed85012d1c0d 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2697,6 +2697,18 @@ static int kvm_vcpu_ioctl_set_lapic(struct kvm_vcpu *vcpu,
 	return 0;
 }
 
+static bool kvm_is_interrupt_allowed(struct kvm_vcpu *vcpu)
+{
+	/*
+	 * Note, .interrupt_allowed() returns -EBUSY if interrupts are allowed
+	 * based on CPU state, but can't be immediately delivered due to a
+	 * pending nested VM-Enter.  Treat that case as "allowed", because
+	 * the goal here is just to check if interrupts are architecturally
+	 * allowed, not to check if they can be injected.
+	 */
+	return kvm_x86_call(interrupt_allowed)(vcpu, false);
+}
+
 static int kvm_cpu_accept_dm_intr(struct kvm_vcpu *vcpu)
 {
 	/*
@@ -2722,7 +2734,7 @@ static int kvm_vcpu_ready_for_interrupt_injection(struct kvm_vcpu *vcpu)
 	 * or KVM_SET_SREGS.  For that to work, we must be at an
 	 * instruction boundary and with no events half-injected.
 	 */
-	return (kvm_arch_interrupt_allowed(vcpu) &&
+	return (kvm_is_interrupt_allowed(vcpu) &&
 		kvm_cpu_accept_dm_intr(vcpu) &&
 		!kvm_event_needs_reinjection(vcpu) &&
 		!kvm_is_exception_pending(vcpu));
@@ -8472,7 +8484,7 @@ bool kvm_vcpu_has_events(struct kvm_vcpu *vcpu)
 	if (kvm_test_request(KVM_REQ_UPDATE_PROTECTED_GUEST_STATE, vcpu))
 		return true;
 
-	if (kvm_arch_interrupt_allowed(vcpu) && kvm_cpu_has_interrupt(vcpu))
+	if (kvm_is_interrupt_allowed(vcpu) && kvm_cpu_has_interrupt(vcpu))
 		return true;
 
 	if (kvm_hv_has_stimer_pending(vcpu))
@@ -10308,11 +10320,6 @@ int kvm_arch_vcpu_should_kick(struct kvm_vcpu *vcpu)
 	return kvm_vcpu_exiting_guest_mode(vcpu) == IN_GUEST_MODE;
 }
 
-int kvm_arch_interrupt_allowed(struct kvm_vcpu *vcpu)
-{
-	return kvm_x86_call(interrupt_allowed)(vcpu, false);
-}
-
 static inline u32 kvm_async_pf_hash_fn(gfn_t gfn)
 {
 	BUILD_BUG_ON(!is_power_of_2(ASYNC_PF_PER_VCPU));
@@ -10448,7 +10455,7 @@ bool kvm_can_do_async_pf(struct kvm_vcpu *vcpu)
 	 * If interrupts are off we cannot even use an artificial
 	 * halt state.
 	 */
-	return kvm_arch_interrupt_allowed(vcpu);
+	return kvm_is_interrupt_allowed(vcpu);
 }
 
 bool kvm_arch_async_page_not_present(struct kvm_vcpu *vcpu,
-- 
2.54.0.1136.gdb2ca164c4-goog