Re: [PATCH v2] riscv: KVM: Add hart-to-vCPU mapping for faster MSI injection

["Nutty.Liu" <nutty.liu@hotmail.com>]

On 10/29/2026 4:24 PM, BillXiang wrote:
> 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 v2:
Hi Bill,

The change log should be under the tear line.
> - 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      | 50 +++++++++++++++++---------------
>   2 files changed, 30 insertions(+), 23 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..a415a8c10967 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;
> @@ -280,6 +282,11 @@ static int aia_init(struct kvm *kvm)
>   		/* Update HART index of the IMSIC based on IMSIC base */
>   		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);
> @@ -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);
> -	}
> -
> -	return 0;
> +	vcpu = xa_load(&aia->hart_to_vcpu, hart_index);
> +	if (!vcpu)
> +		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)
> @@ -647,9 +648,12 @@ 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);