[PATCH v5 2/2] RISC-V: KVM: AIA: Make HGEI number management fully per-CPU

[Anup Patel <anup.patel@oss.qualcomm.com>]

From: "Guo Ren (Alibaba DAMO Academy)" <guoren@kernel.org>

Previously, the number of Hypervisor Guest External Interrupt (HGEI)
lines was stored in a single global variable `kvm_riscv_aia_nr_hgei`
and assumed to be the same for all HARTs. This assumption does not
hold on heterogeneous RISC-V SoCs where different cores may expose
different HGEIE CSR widths.

Introduce `nr_hgei` field into the per-CPU `struct aia_hgei_control`
and probe the actual supported HGEI count for the current HART in
`kvm_riscv_aia_enable()` using the standard RISC-V CSR probe technique:

    csr_write(CSR_HGEIE, -1UL);
    nr = fls_long(csr_read(CSR_HGEIE));
    if (nr)
        nr--;

All HGEI allocation, free and disable paths (`kvm_riscv_aia_free_hgei()`,
`kvm_riscv_aia_disable()`, etc.) now use the per-CPU value instead of
the global one.

The global `kvm_riscv_aia_nr_hgei` now represents the minimum number
of HGEI lines across HARTs and can be used to check whether HGEI
support is available or not.

This makes KVM AIA robust on big.LITTLE-style asymmetric platforms.

Signed-off-by: Guo Ren (Alibaba DAMO Academy) <guoren@kernel.org>
Signed-off-by: Anup Patel <anup.patel@oss.qualcomm.com>
---
 arch/riscv/include/asm/kvm_aia.h |  2 +-
 arch/riscv/kvm/aia.c             | 88 +++++++++++++++++++-------------
 arch/riscv/kvm/aia_device.c      |  4 +-
 arch/riscv/kvm/main.c            |  8 +--
 4 files changed, 60 insertions(+), 42 deletions(-)

diff --git a/arch/riscv/include/asm/kvm_aia.h b/arch/riscv/include/asm/kvm_aia.h
index b04ecdd1a860..c67ec5ac0a14 100644
--- a/arch/riscv/include/asm/kvm_aia.h
+++ b/arch/riscv/include/asm/kvm_aia.h
@@ -79,7 +79,7 @@ struct kvm_vcpu_aia {
 
 #define irqchip_in_kernel(k)		((k)->arch.aia.in_kernel)
 
-extern unsigned int kvm_riscv_aia_nr_hgei;
+extern atomic_t kvm_riscv_aia_nr_hgei;
 extern unsigned int kvm_riscv_aia_max_ids;
 DECLARE_STATIC_KEY_FALSE(kvm_riscv_aia_available);
 #define kvm_riscv_aia_available() \
diff --git a/arch/riscv/kvm/aia.c b/arch/riscv/kvm/aia.c
index 5ec503288555..bafb009c5ce5 100644
--- a/arch/riscv/kvm/aia.c
+++ b/arch/riscv/kvm/aia.c
@@ -21,13 +21,15 @@
 
 struct aia_hgei_control {
 	raw_spinlock_t lock;
+	bool free_bitmap_initialized;
 	unsigned long free_bitmap;
 	struct kvm_vcpu *owners[BITS_PER_LONG];
+	unsigned int nr_hgei;
 };
 static DEFINE_PER_CPU(struct aia_hgei_control, aia_hgei);
 static int hgei_parent_irq;
 
-unsigned int kvm_riscv_aia_nr_hgei;
+atomic_t kvm_riscv_aia_nr_hgei;
 unsigned int kvm_riscv_aia_max_ids;
 DEFINE_STATIC_KEY_FALSE(kvm_riscv_aia_available);
 
@@ -452,7 +454,7 @@ void kvm_riscv_aia_free_hgei(int cpu, int hgei)
 
 	raw_spin_lock_irqsave(&hgctrl->lock, flags);
 
-	if (hgei > 0 && hgei <= kvm_riscv_aia_nr_hgei) {
+	if (hgei > 0 && hgei <= hgctrl->nr_hgei) {
 		if (!(hgctrl->free_bitmap & BIT(hgei))) {
 			hgctrl->free_bitmap |= BIT(hgei);
 			hgctrl->owners[hgei] = NULL;
@@ -486,26 +488,18 @@ static irqreturn_t hgei_interrupt(int irq, void *dev_id)
 
 static int aia_hgei_init(void)
 {
-	int cpu, rc;
-	struct irq_domain *domain;
 	struct aia_hgei_control *hgctrl;
+	struct irq_domain *domain;
+	int cpu, rc;
 
 	/* Initialize per-CPU guest external interrupt line management */
 	for_each_possible_cpu(cpu) {
 		hgctrl = per_cpu_ptr(&aia_hgei, cpu);
 		raw_spin_lock_init(&hgctrl->lock);
-		if (kvm_riscv_aia_nr_hgei) {
-			hgctrl->free_bitmap =
-				BIT(kvm_riscv_aia_nr_hgei + 1) - 1;
-			hgctrl->free_bitmap &= ~BIT(0);
-		} else
-			hgctrl->free_bitmap = 0;
+		hgctrl->free_bitmap_initialized = false;
+		hgctrl->free_bitmap = 0;
 	}
 
-	/* Skip SGEI interrupt setup for zero guest external interrupts */
-	if (!kvm_riscv_aia_nr_hgei)
-		goto skip_sgei_interrupt;
-
 	/* Find INTC irq domain */
 	domain = irq_find_matching_fwnode(riscv_get_intc_hwnode(),
 					  DOMAIN_BUS_ANY);
@@ -529,25 +523,60 @@ static int aia_hgei_init(void)
 		return rc;
 	}
 
-skip_sgei_interrupt:
 	return 0;
 }
 
 static void aia_hgei_exit(void)
 {
-	/* Do nothing for zero guest external interrupts */
-	if (!kvm_riscv_aia_nr_hgei)
-		return;
-
 	/* Free per-CPU SGEI interrupt */
 	free_percpu_irq(hgei_parent_irq, &aia_hgei);
 }
 
 void kvm_riscv_aia_enable(void)
 {
+	const struct imsic_global_config *gc;
+	const struct imsic_local_config *lc;
+	struct aia_hgei_control *hgctrl;
+	unsigned long flags;
+	int aia_nr_hgei;
+
 	if (!kvm_riscv_aia_available())
 		return;
 
+	gc = imsic_get_global_config();
+	lc = (gc) ? this_cpu_ptr(gc->local) : NULL;
+	hgctrl = this_cpu_ptr(&aia_hgei);
+
+	/* Figure-out number of bits in HGEIE */
+	csr_write(CSR_HGEIE, -1UL);
+	hgctrl->nr_hgei = fls_long(csr_read(CSR_HGEIE));
+	csr_write(CSR_HGEIE, 0);
+	if (hgctrl->nr_hgei)
+		hgctrl->nr_hgei--;
+
+	/*
+	 * Number of usable per-HART HGEI lines should be minimum of
+	 * per-HART IMSIC guest files and number of bits in HGEIE.
+	 */
+	if (lc)
+		hgctrl->nr_hgei = min((ulong)hgctrl->nr_hgei, lc->nr_guest_files);
+	else
+		hgctrl->nr_hgei = 0;
+
+	/* Update the number of IMSIC guest files across all HARTs */
+	aia_nr_hgei = atomic_read(&kvm_riscv_aia_nr_hgei);
+	do {
+		if (aia_nr_hgei <= hgctrl->nr_hgei)
+			break;
+	} while (!atomic_try_cmpxchg(&kvm_riscv_aia_nr_hgei, &aia_nr_hgei, hgctrl->nr_hgei));
+
+	raw_spin_lock_irqsave(&hgctrl->lock, flags);
+	if (!hgctrl->free_bitmap_initialized) {
+		hgctrl->free_bitmap = (hgctrl->nr_hgei) ? GENMASK_ULL(hgctrl->nr_hgei, 1) : 0;
+		hgctrl->free_bitmap_initialized = true;
+	}
+	raw_spin_unlock_irqrestore(&hgctrl->lock, flags);
+
 	csr_write(CSR_HVICTL, aia_hvictl_value(false));
 	csr_write(CSR_HVIPRIO1, 0x0);
 	csr_write(CSR_HVIPRIO2, 0x0);
@@ -588,7 +617,7 @@ void kvm_riscv_aia_disable(void)
 
 	raw_spin_lock_irqsave(&hgctrl->lock, flags);
 
-	for (i = 0; i <= kvm_riscv_aia_nr_hgei; i++) {
+	for (i = 0; i <= hgctrl->nr_hgei; i++) {
 		vcpu = hgctrl->owners[i];
 		if (!vcpu)
 			continue;
@@ -628,26 +657,15 @@ int kvm_riscv_aia_init(void)
 		return -ENODEV;
 	gc = imsic_get_global_config();
 
-	/* Figure-out number of bits in HGEIE */
-	csr_write(CSR_HGEIE, -1UL);
-	kvm_riscv_aia_nr_hgei = fls_long(csr_read(CSR_HGEIE));
-	csr_write(CSR_HGEIE, 0);
-	if (kvm_riscv_aia_nr_hgei)
-		kvm_riscv_aia_nr_hgei--;
-
-	/*
-	 * Number of usable HGEI lines should be minimum of per-HART
-	 * IMSIC guest files and number of bits in HGEIE
-	 */
+	/* Set initial value of IMSIC guest files across all HARTs */
 	if (gc)
-		kvm_riscv_aia_nr_hgei = min((ulong)kvm_riscv_aia_nr_hgei,
-					    gc->nr_guest_files);
+		atomic_set(&kvm_riscv_aia_nr_hgei, gc->nr_guest_files);
 	else
-		kvm_riscv_aia_nr_hgei = 0;
+		atomic_set(&kvm_riscv_aia_nr_hgei, 0);
 
 	/* Find number of guest MSI IDs */
 	kvm_riscv_aia_max_ids = IMSIC_MAX_ID;
-	if (gc && kvm_riscv_aia_nr_hgei)
+	if (gc)
 		kvm_riscv_aia_max_ids = gc->nr_guest_ids + 1;
 
 	/* Initialize guest external interrupt line management */
diff --git a/arch/riscv/kvm/aia_device.c b/arch/riscv/kvm/aia_device.c
index 3d1e81e2a36b..be83c2d5fc30 100644
--- a/arch/riscv/kvm/aia_device.c
+++ b/arch/riscv/kvm/aia_device.c
@@ -71,7 +71,7 @@ static int aia_config(struct kvm *kvm, unsigned long type,
 				 * external interrupts (i.e. non-zero
 				 * VS-level IMSIC pages).
 				 */
-				if (!kvm_riscv_aia_nr_hgei)
+				if (!atomic_read(&kvm_riscv_aia_nr_hgei))
 					return -EINVAL;
 				break;
 			default:
@@ -628,7 +628,7 @@ void kvm_riscv_aia_init_vm(struct kvm *kvm)
 	 */
 
 	/* Initialize default values in AIA global context */
-	aia->mode = (kvm_riscv_aia_nr_hgei) ?
+	aia->mode = (atomic_read(&kvm_riscv_aia_nr_hgei)) ?
 		KVM_DEV_RISCV_AIA_MODE_AUTO : KVM_DEV_RISCV_AIA_MODE_EMUL;
 	aia->nr_ids = kvm_riscv_aia_max_ids - 1;
 	aia->nr_sources = 0;
diff --git a/arch/riscv/kvm/main.c b/arch/riscv/kvm/main.c
index cb8a65273c1f..0924c75100a2 100644
--- a/arch/riscv/kvm/main.c
+++ b/arch/riscv/kvm/main.c
@@ -168,10 +168,6 @@ static int __init riscv_kvm_init(void)
 
 	kvm_info("VMID %ld bits available\n", kvm_riscv_gstage_vmid_bits());
 
-	if (kvm_riscv_aia_available())
-		kvm_info("AIA available with %d guest external interrupts\n",
-			 kvm_riscv_aia_nr_hgei);
-
 	kvm_riscv_setup_vendor_features();
 
 	kvm_register_perf_callbacks();
@@ -182,6 +178,10 @@ static int __init riscv_kvm_init(void)
 		return rc;
 	}
 
+	if (kvm_riscv_aia_available())
+		kvm_info("AIA available with %d guest external interrupts\n",
+			 atomic_read(&kvm_riscv_aia_nr_hgei));
+
 	return 0;
 }
 module_init(riscv_kvm_init);
-- 
2.43.0