x86/irq: Remove bitfields in posted interrupt descriptor

Mixture of bitfields and types is weird and really not intuitive, remove
bitfields and use typed data exclusively. Bitfields often result in
inferior machine code.

Suggested-by: Sean Christopherson <[email protected]>
Suggested-by: Thomas Gleixner <[email protected]>
Signed-off-by: Jacob Pan <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Link: https://lore.kernel.org/all/20240404101735.402feec8@jacob-builder/T/#mf66e34a82a48f4d8e2926b5581eff59a122de53a

Author: Jacob Pan

arch/x86/include/asm/posted_intr.h

@@ -15,17 +15,9 @@ struct pi_desc {
 	};
 	union {
 		struct {
-				/* bit 256 - Outstanding Notification */
-			u16	on	: 1,
-				/* bit 257 - Suppress Notification */
-				sn	: 1,
-				/* bit 271:258 - Reserved */
-				rsvd_1	: 14;
-				/* bit 279:272 - Notification Vector */
+			u16	notifications; /* Suppress and outstanding bits */
 			u8	nv;
-				/* bit 287:280 - Reserved */
 			u8	rsvd_2;
-				/* bit 319:288 - Notification Destination */
 			u32	ndst;
 		};
 		u64 control;
@@ -88,4 +80,15 @@ static inline bool pi_test_sn(struct pi_desc *pi_desc)
 	return test_bit(POSTED_INTR_SN, (unsigned long *)&pi_desc->control);
 }
 
+/* Non-atomic helpers */
+static inline void __pi_set_sn(struct pi_desc *pi_desc)
+{
+	pi_desc->notifications |= BIT(POSTED_INTR_SN);
+}
+
+static inline void __pi_clear_sn(struct pi_desc *pi_desc)
+{
+	pi_desc->notifications &= ~BIT(POSTED_INTR_SN);
+}
+
 #endif /* _X86_POSTED_INTR_H */

arch/x86/kvm/vmx/posted_intr.c

@@ -107,7 +107,7 @@ void vmx_vcpu_pi_load(struct kvm_vcpu *vcpu, int cpu)
 		 * handle task migration (@cpu != vcpu->cpu).
 		 */
 		new.ndst = dest;
-		new.sn = 0;
+		__pi_clear_sn(&new);
 
 		/*
 		 * Restore the notification vector; in the blocking case, the
@@ -157,7 +157,7 @@ static void pi_enable_wakeup_handler(struct kvm_vcpu *vcpu)
 		      &per_cpu(wakeup_vcpus_on_cpu, vcpu->cpu));
 	raw_spin_unlock(&per_cpu(wakeup_vcpus_on_cpu_lock, vcpu->cpu));
 
-	WARN(pi_desc->sn, "PI descriptor SN field set before blocking");
+	WARN(pi_test_sn(pi_desc), "PI descriptor SN field set before blocking");
 
 	old.control = READ_ONCE(pi_desc->control);
 	do {

arch/x86/kvm/vmx/vmx.c

@@ -4845,7 +4845,7 @@ static void __vmx_vcpu_reset(struct kvm_vcpu *vcpu)
 	 * or POSTED_INTR_WAKEUP_VECTOR.
 	 */
 	vmx->pi_desc.nv = POSTED_INTR_VECTOR;
-	vmx->pi_desc.sn = 1;
+	__pi_set_sn(&vmx->pi_desc);
 }
 
 static void vmx_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)