Merge tag 'kvm-x86-pir-6.16' of https://github.com/kvm-x86/linux into HEAD

KVM x86 posted interrupt changes for 6.16:

Refine and optimize KVM's software processing of the PIR, and ultimately share
PIR harvesting code between KVM and the kernel's Posted MSI handler

Author: bonzini

arch/x86/include/asm/posted_intr.h

@@ -1,19 +1,24 @@
 /* SPDX-License-Identifier: GPL-2.0 */
 #ifndef _X86_POSTED_INTR_H
 #define _X86_POSTED_INTR_H
+
+#include <asm/cmpxchg.h>
+#include <asm/rwonce.h>
 #include <asm/irq_vectors.h>
 
+#include <linux/bitmap.h>
+
 #define POSTED_INTR_ON  0
 #define POSTED_INTR_SN  1
 
 #define PID_TABLE_ENTRY_VALID 1
 
+#define NR_PIR_VECTORS	256
+#define NR_PIR_WORDS	(NR_PIR_VECTORS / BITS_PER_LONG)
+
 /* Posted-Interrupt Descriptor */
 struct pi_desc {
-	union {
-		u32 pir[8];     /* Posted interrupt requested */
-		u64 pir64[4];
-	};
+	unsigned long pir[NR_PIR_WORDS];     /* Posted interrupt requested */
 	union {
 		struct {
 			u16	notifications; /* Suppress and outstanding bits */
@@ -26,6 +31,65 @@ struct pi_desc {
 	u32 rsvd[6];
 } __aligned(64);
 
+/*
+ * De-multiplexing posted interrupts is on the performance path, the code
+ * below is written to optimize the cache performance based on the following
+ * considerations:
+ * 1.Posted interrupt descriptor (PID) fits in a cache line that is frequently
+ *   accessed by both CPU and IOMMU.
+ * 2.During software processing of posted interrupts, the CPU needs to do
+ *   natural width read and xchg for checking and clearing posted interrupt
+ *   request (PIR), a 256 bit field within the PID.
+ * 3.On the other side, the IOMMU does atomic swaps of the entire PID cache
+ *   line when posting interrupts and setting control bits.
+ * 4.The CPU can access the cache line a magnitude faster than the IOMMU.
+ * 5.Each time the IOMMU does interrupt posting to the PIR will evict the PID
+ *   cache line. The cache line states after each operation are as follows,
+ *   assuming a 64-bit kernel:
+ *   CPU		IOMMU			PID Cache line state
+ *   ---------------------------------------------------------------
+ *...read64					exclusive
+ *...lock xchg64				modified
+ *...			post/atomic swap	invalid
+ *...-------------------------------------------------------------
+ *
+ * To reduce L1 data cache miss, it is important to avoid contention with
+ * IOMMU's interrupt posting/atomic swap. Therefore, a copy of PIR is used
+ * when processing posted interrupts in software, e.g. to dispatch interrupt
+ * handlers for posted MSIs, or to move interrupts from the PIR to the vIRR
+ * in KVM.
+ *
+ * In addition, the code is trying to keep the cache line state consistent
+ * as much as possible. e.g. when making a copy and clearing the PIR
+ * (assuming non-zero PIR bits are present in the entire PIR), it does:
+ *		read, read, read, read, xchg, xchg, xchg, xchg
+ * instead of:
+ *		read, xchg, read, xchg, read, xchg, read, xchg
+ */
+static __always_inline bool pi_harvest_pir(unsigned long *pir,
+					   unsigned long *pir_vals)
+{
+	unsigned long pending = 0;
+	int i;
+
+	for (i = 0; i < NR_PIR_WORDS; i++) {
+		pir_vals[i] = READ_ONCE(pir[i]);
+		pending |= pir_vals[i];
+	}
+
+	if (!pending)
+		return false;
+
+	for (i = 0; i < NR_PIR_WORDS; i++) {
+		if (!pir_vals[i])
+			continue;
+
+		pir_vals[i] = arch_xchg(&pir[i], 0);
+	}
+
+	return true;
+}
+
 static inline bool pi_test_and_set_on(struct pi_desc *pi_desc)
 {
 	return test_and_set_bit(POSTED_INTR_ON, (unsigned long *)&pi_desc->control);
@@ -43,12 +107,12 @@ static inline bool pi_test_and_clear_sn(struct pi_desc *pi_desc)
 
 static inline bool pi_test_and_set_pir(int vector, struct pi_desc *pi_desc)
 {
-	return test_and_set_bit(vector, (unsigned long *)pi_desc->pir);
+	return test_and_set_bit(vector, pi_desc->pir);
 }
 
 static inline bool pi_is_pir_empty(struct pi_desc *pi_desc)
 {
-	return bitmap_empty((unsigned long *)pi_desc->pir, NR_VECTORS);
+	return bitmap_empty(pi_desc->pir, NR_VECTORS);
 }
 
 static inline void pi_set_sn(struct pi_desc *pi_desc)
@@ -110,7 +174,7 @@ static inline bool pi_pending_this_cpu(unsigned int vector)
 	if (WARN_ON_ONCE(vector > NR_VECTORS || vector < FIRST_EXTERNAL_VECTOR))
 		return false;
 
-	return test_bit(vector, (unsigned long *)pid->pir);
+	return test_bit(vector, pid->pir);
 }
 
 extern void intel_posted_msi_init(void);

arch/x86/kernel/irq.c

@@ -380,61 +380,18 @@ void intel_posted_msi_init(void)
 	this_cpu_write(posted_msi_pi_desc.ndst, destination);
 }
 
-/*
- * De-multiplexing posted interrupts is on the performance path, the code
- * below is written to optimize the cache performance based on the following
- * considerations:
- * 1.Posted interrupt descriptor (PID) fits in a cache line that is frequently
- *   accessed by both CPU and IOMMU.
- * 2.During posted MSI processing, the CPU needs to do 64-bit read and xchg
- *   for checking and clearing posted interrupt request (PIR), a 256 bit field
- *   within the PID.
- * 3.On the other side, the IOMMU does atomic swaps of the entire PID cache
- *   line when posting interrupts and setting control bits.
- * 4.The CPU can access the cache line a magnitude faster than the IOMMU.
- * 5.Each time the IOMMU does interrupt posting to the PIR will evict the PID
- *   cache line. The cache line states after each operation are as follows:
- *   CPU		IOMMU			PID Cache line state
- *   ---------------------------------------------------------------
- *...read64					exclusive
- *...lock xchg64				modified
- *...			post/atomic swap	invalid
- *...-------------------------------------------------------------
- *
- * To reduce L1 data cache miss, it is important to avoid contention with
- * IOMMU's interrupt posting/atomic swap. Therefore, a copy of PIR is used
- * to dispatch interrupt handlers.
- *
- * In addition, the code is trying to keep the cache line state consistent
- * as much as possible. e.g. when making a copy and clearing the PIR
- * (assuming non-zero PIR bits are present in the entire PIR), it does:
- *		read, read, read, read, xchg, xchg, xchg, xchg
- * instead of:
- *		read, xchg, read, xchg, read, xchg, read, xchg
- */
-static __always_inline bool handle_pending_pir(u64 *pir, struct pt_regs *regs)
+static __always_inline bool handle_pending_pir(unsigned long *pir, struct pt_regs *regs)
 {
-	int i, vec = FIRST_EXTERNAL_VECTOR;
-	unsigned long pir_copy[4];
-	bool handled = false;
+	unsigned long pir_copy[NR_PIR_WORDS];
+	int vec = FIRST_EXTERNAL_VECTOR;
 
-	for (i = 0; i < 4; i++)
-		pir_copy[i] = pir[i];
-
-	for (i = 0; i < 4; i++) {
-		if (!pir_copy[i])
-			continue;
+	if (!pi_harvest_pir(pir, pir_copy))
+		return false;
 
-		pir_copy[i] = arch_xchg(&pir[i], 0);
-		handled = true;
-	}
-
-	if (handled) {
-		for_each_set_bit_from(vec, pir_copy, FIRST_SYSTEM_VECTOR)
-			call_irq_handler(vec, regs);
-	}
+	for_each_set_bit_from(vec, pir_copy, FIRST_SYSTEM_VECTOR)
+		call_irq_handler(vec, regs);
 
-	return handled;
+	return true;
 }
 
 /*
@@ -464,7 +421,7 @@ DEFINE_IDTENTRY_SYSVEC(sysvec_posted_msi_notification)
 	 * MAX_POSTED_MSI_COALESCING_LOOP - 1 loops are executed here.
 	 */
 	while (++i < MAX_POSTED_MSI_COALESCING_LOOP) {
-		if (!handle_pending_pir(pid->pir64, regs))
+		if (!handle_pending_pir(pid->pir, regs))
 			break;
 	}
 
@@ -479,7 +436,7 @@ DEFINE_IDTENTRY_SYSVEC(sysvec_posted_msi_notification)
 	 * process PIR bits one last time such that handling the new interrupts
 	 * are not delayed until the next IRQ.
 	 */
-	handle_pending_pir(pid->pir64, regs);
+	handle_pending_pir(pid->pir, regs);
 
 	apic_eoi();
 	irq_exit();

arch/x86/kvm/lapic.c

@@ -655,27 +655,29 @@ static u8 count_vectors(void *bitmap)
 	return count;
 }
 
-bool __kvm_apic_update_irr(u32 *pir, void *regs, int *max_irr)
+bool __kvm_apic_update_irr(unsigned long *pir, void *regs, int *max_irr)
 {
+	unsigned long pir_vals[NR_PIR_WORDS];
+	u32 *__pir = (void *)pir_vals;
 	u32 i, vec;
-	u32 pir_val, irr_val, prev_irr_val;
+	u32 irr_val, prev_irr_val;
 	int max_updated_irr;
 
 	max_updated_irr = -1;
 	*max_irr = -1;
 
+	if (!pi_harvest_pir(pir, pir_vals))
+		return false;
+
 	for (i = vec = 0; i <= 7; i++, vec += 32) {
 		u32 *p_irr = (u32 *)(regs + APIC_IRR + i * 0x10);
 
-		irr_val = *p_irr;
-		pir_val = READ_ONCE(pir[i]);
-
-		if (pir_val) {
-			pir_val = xchg(&pir[i], 0);
+		irr_val = READ_ONCE(*p_irr);
 
+		if (__pir[i]) {
 			prev_irr_val = irr_val;
 			do {
-				irr_val = prev_irr_val | pir_val;
+				irr_val = prev_irr_val | __pir[i];
 			} while (prev_irr_val != irr_val &&
 				 !try_cmpxchg(p_irr, &prev_irr_val, irr_val));
 
@@ -691,7 +693,7 @@ bool __kvm_apic_update_irr(u32 *pir, void *regs, int *max_irr)
 }
 EXPORT_SYMBOL_GPL(__kvm_apic_update_irr);
 
-bool kvm_apic_update_irr(struct kvm_vcpu *vcpu, u32 *pir, int *max_irr)
+bool kvm_apic_update_irr(struct kvm_vcpu *vcpu, unsigned long *pir, int *max_irr)
 {
 	struct kvm_lapic *apic = vcpu->arch.apic;
 	bool irr_updated = __kvm_apic_update_irr(pir, apic->regs, max_irr);

arch/x86/kvm/lapic.h

@@ -103,8 +103,8 @@ bool kvm_apic_match_dest(struct kvm_vcpu *vcpu, struct kvm_lapic *source,
 			   int shorthand, unsigned int dest, int dest_mode);
 int kvm_apic_compare_prio(struct kvm_vcpu *vcpu1, struct kvm_vcpu *vcpu2);
 void kvm_apic_clear_irr(struct kvm_vcpu *vcpu, int vec);
-bool __kvm_apic_update_irr(u32 *pir, void *regs, int *max_irr);
-bool kvm_apic_update_irr(struct kvm_vcpu *vcpu, u32 *pir, int *max_irr);
+bool __kvm_apic_update_irr(unsigned long *pir, void *regs, int *max_irr);
+bool kvm_apic_update_irr(struct kvm_vcpu *vcpu, unsigned long *pir, int *max_irr);
 void kvm_apic_update_ppr(struct kvm_vcpu *vcpu);
 int kvm_apic_set_irq(struct kvm_vcpu *vcpu, struct kvm_lapic_irq *irq,
 		     struct dest_map *dest_map);

arch/x86/kvm/vmx/posted_intr.h

@@ -20,7 +20,7 @@ static inline int pi_find_highest_vector(struct pi_desc *pi_desc)
 {
 	int vec;
 
-	vec = find_last_bit((unsigned long *)pi_desc->pir, 256);
+	vec = find_last_bit(pi_desc->pir, 256);
 	return vec < 256 ? vec : -1;
 }