[PATCH v3] riscv: KVM: Add hart-to-vCPU mapping for faster MSI injection

[PATCH v3] riscv: KVM: Add hart-to-vCPU mapping for faster MSI injection

[BillXiang]

Replace linear searches over all vCPUs in MSI injection paths with a
hart_index -> vCPU xarray lookup table. This avoids O(n) scans on
every injected interrupt and improves performance when the number of
vCPUs is large.

Both kvm_riscv_aia_inject_msi_by_id() and kvm_riscv_aia_inject_msi()
now use the table instead of iterating over the vCPU list.

Signed-off-by: BillXiang <xiangwencheng@lanxincomputing.com>
---
Changes in v3:
- Fix format.

Changes in v2:
- Use xarray instead of normal array to handle incontiguous hart_index.
- Link to v1:
  https://lore.kernel.org/kvm-riscv/20260730093614.983508-1-xiangwencheng@lanxincomputing.com/
---
 arch/riscv/include/asm/kvm_aia.h |  3 ++
 arch/riscv/kvm/aia_device.c      | 48 +++++++++++++++++---------------
 2 files changed, 29 insertions(+), 22 deletions(-)

diff --git a/arch/riscv/include/asm/kvm_aia.h b/arch/riscv/include/asm/kvm_aia.h
index ab03f853e507..3b075f18e1d6 100644
--- a/arch/riscv/include/asm/kvm_aia.h
+++ b/arch/riscv/include/asm/kvm_aia.h
@@ -12,6 +12,7 @@
 
 #include <linux/jump_label.h>
 #include <linux/kvm_types.h>
+#include <linux/xarray.h>
 #include <asm/csr.h>
 
 struct kvm_aia {
@@ -47,6 +48,8 @@ struct kvm_aia {
 
 	/* Internal state of APLIC */
 	void		*aplic_state;
+
+	struct xarray hart_to_vcpu;
 };
 
 struct kvm_vcpu_aia_csr {
diff --git a/arch/riscv/kvm/aia_device.c b/arch/riscv/kvm/aia_device.c
index efc7c0bcfba9..b76ce0b4669a 100644
--- a/arch/riscv/kvm/aia_device.c
+++ b/arch/riscv/kvm/aia_device.c
@@ -259,6 +259,8 @@ static int aia_init(struct kvm *kvm)
 	if (ret)
 		return ret;
 
+	xa_init(&aia->hart_to_vcpu);
+
 	/* Iterate over each VCPU */
 	kvm_for_each_vcpu(idx, vcpu, kvm) {
 		vaia = &vcpu->arch.aia_context;
@@ -281,6 +283,11 @@ static int aia_init(struct kvm *kvm)
 		vaia->hart_index = aia_imsic_hart_index(aia,
 							vaia->imsic_addr);
 
+		ret = xa_insert(&aia->hart_to_vcpu, vaia->hart_index,
+				vcpu, GFP_KERNEL);
+		if (ret)
+			goto fail_cleanup_imsics;
+
 		/* Initialize IMSIC for this VCPU */
 		ret = kvm_riscv_vcpu_aia_imsic_init(vcpu);
 		if (ret)
@@ -299,6 +306,7 @@ static int aia_init(struct kvm *kvm)
 			continue;
 		kvm_riscv_vcpu_aia_imsic_cleanup(vcpu);
 	}
+	xa_destroy(&aia->hart_to_vcpu);
 	kvm_riscv_aia_aplic_cleanup(kvm);
 	return ret;
 }
@@ -557,30 +565,25 @@ void kvm_riscv_vcpu_aia_deinit(struct kvm_vcpu *vcpu)
 int kvm_riscv_aia_inject_msi_by_id(struct kvm *kvm, u32 hart_index,
 				   u32 guest_index, u32 iid)
 {
-	unsigned long idx;
 	struct kvm_vcpu *vcpu;
+	struct kvm_aia *aia = &kvm->arch.aia;
 
 	/* Proceed only if AIA was initialized successfully */
 	if (!kvm_riscv_aia_initialized(kvm))
 		return -EBUSY;
 
-	/* Inject MSI to matching VCPU */
-	kvm_for_each_vcpu(idx, vcpu, kvm) {
-		if (vcpu->arch.aia_context.hart_index == hart_index)
-			return kvm_riscv_vcpu_aia_imsic_inject(vcpu,
-							       guest_index,
-							       0, iid);
-	}
+	vcpu = xa_load(&aia->hart_to_vcpu, hart_index);
+	if (!vcpu)
+		return 0;
 
-	return 0;
+	return kvm_riscv_vcpu_aia_imsic_inject(vcpu, guest_index, 0, iid);
 }
 
 int kvm_riscv_aia_inject_msi(struct kvm *kvm, struct kvm_msi *msi)
 {
 	gpa_t tppn, ippn;
-	unsigned long idx;
 	struct kvm_vcpu *vcpu;
-	u32 g, toff, iid = msi->data;
+	u32 g, toff, iid = msi->data, hart_index;
 	struct kvm_aia *aia = &kvm->arch.aia;
 	gpa_t target = (((gpa_t)msi->address_hi) << 32) | msi->address_lo;
 
@@ -595,18 +598,16 @@ int kvm_riscv_aia_inject_msi(struct kvm *kvm, struct kvm_msi *msi)
 	g = tppn & (BIT(aia->nr_guest_bits) - 1);
 	tppn &= ~((gpa_t)(BIT(aia->nr_guest_bits) - 1));
 
-	/* Inject MSI to matching VCPU */
-	kvm_for_each_vcpu(idx, vcpu, kvm) {
-		ippn = vcpu->arch.aia_context.imsic_addr >>
-					IMSIC_MMIO_PAGE_SHIFT;
-		if (ippn == tppn) {
-			toff = target & (IMSIC_MMIO_PAGE_SZ - 1);
-			return kvm_riscv_vcpu_aia_imsic_inject(vcpu, g,
-							       toff, iid);
-		}
-	}
+	hart_index = aia_imsic_hart_index(aia, target);
+	vcpu = xa_load(&aia->hart_to_vcpu, hart_index);
+	if (!vcpu)
+		return 0;
 
-	return 0;
+	ippn = vcpu->arch.aia_context.imsic_addr >> IMSIC_MMIO_PAGE_SHIFT;
+	if (ippn != tppn)
+		return 0;
+	toff = target & (IMSIC_MMIO_PAGE_SZ - 1);
+	return kvm_riscv_vcpu_aia_imsic_inject(vcpu, g, toff, iid);
 }
 
 int kvm_riscv_aia_inject_irq(struct kvm *kvm, unsigned int irq, bool level)
@@ -647,10 +648,13 @@ void kvm_riscv_aia_init_vm(struct kvm *kvm)
 
 void kvm_riscv_aia_destroy_vm(struct kvm *kvm)
 {
+	struct kvm_aia *aia = &kvm->arch.aia;
 	/* Proceed only if AIA was initialized successfully */
 	if (!kvm_riscv_aia_initialized(kvm))
 		return;
 
+	xa_destroy(&aia->hart_to_vcpu);
+
 	/* Cleanup APLIC context */
 	kvm_riscv_aia_aplic_cleanup(kvm);
 }
-- 
2.53.0