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

[Anup Patel]

On Thu, Jul 30, 2026 at 3:06 PM BillXiang
<xiangwencheng at lanxincomputing.com> wrote:
>
> Replace linear searches over all vCPUs in MSI injection paths with a
> direct hart_index -> vCPU 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.

The AIA hart_index bits for VCPUs are based on the IMSIC address
set by the KVM user-space and are not required to be contiguous hence
this patch is already broken.

NACK from my side.

Regards,
Anup

>
> Signed-off-by: BillXiang <xiangwencheng at lanxincomputing.com>
> ---
>  arch/riscv/include/asm/kvm_aia.h |  2 +
>  arch/riscv/kvm/aia_device.c      | 67 +++++++++++++++++++++-----------
>  2 files changed, 47 insertions(+), 22 deletions(-)
>
> diff --git a/arch/riscv/include/asm/kvm_aia.h b/arch/riscv/include/asm/kvm_aia.h
> index c67ec5ac0..71240b0a2 100644
> --- a/arch/riscv/include/asm/kvm_aia.h
> +++ b/arch/riscv/include/asm/kvm_aia.h
> @@ -47,6 +47,8 @@ struct kvm_aia {
>
>         /* Internal state of APLIC */
>         void            *aplic_state;
> +
> +       struct kvm_vcpu **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 be83c2d5f..595553817 100644
> --- a/arch/riscv/kvm/aia_device.c
> +++ b/arch/riscv/kvm/aia_device.c
> @@ -253,6 +253,14 @@ static int aia_init(struct kvm *kvm)
>         if (ret)
>                 return ret;
>
> +       aia->hart_to_vcpu = kcalloc(kvm->created_vcpus,
> +                                       sizeof(struct kvm_vcpu*),
> +                                       GFP_KERNEL);
> +       if (!aia->hart_to_vcpu) {
> +               ret = -ENOMEM;
> +               goto fail_cleanup_aplic;
> +       }
> +
>         /* Iterate over each VCPU */
>         kvm_for_each_vcpu(idx, vcpu, kvm) {
>                 vaia = &vcpu->arch.aia_context;
> @@ -274,6 +282,12 @@ 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);
> +
> +               if (aia->hart_to_vcpu[vaia->hart_index]) {
> +                       ret = -EINVAL;
> +                       goto fail_cleanup_imsics;
> +               }
> +               aia->hart_to_vcpu[vaia->hart_index] = vcpu;
>
>                 /* Initialize IMSIC for this VCPU */
>                 ret = kvm_riscv_vcpu_aia_imsic_init(vcpu);
> @@ -293,6 +307,9 @@ static int aia_init(struct kvm *kvm)
>                         continue;
>                 kvm_riscv_vcpu_aia_imsic_cleanup(vcpu);
>         }
> +       kfree(aia->hart_to_vcpu);
> +       aia->hart_to_vcpu = NULL;
> +fail_cleanup_aplic:
>         kvm_riscv_aia_aplic_cleanup(kvm);
>         return ret;
>  }
> @@ -551,30 +568,28 @@ 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);
> -       }
> +       if (!aia->hart_to_vcpu || hart_index >= kvm->created_vcpus)
> +               return 0;
>
> -       return 0;
> +       vcpu = 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;
>
> @@ -589,18 +604,22 @@ 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);
> -               }
> -       }
> +       if (!aia->hart_to_vcpu)
> +               return 0;
>
> -       return 0;
> +       hart_index = aia_imsic_hart_index(aia, target);
> +       if(hart_index >= kvm->created_vcpus)
> +               return 0;
> +
> +       vcpu = aia->hart_to_vcpu[hart_index];
> +       if (!vcpu)
> +               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)
> @@ -641,10 +660,14 @@ 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;
>
> +       kfree(aia->hart_to_vcpu);
> +       aia->hart_to_vcpu = NULL;
> +
>         /* Cleanup APLIC context */
>         kvm_riscv_aia_aplic_cleanup(kvm);
>  }
> --
> 2.53.0