[PATCH] riscv: KVM: Add hart-to-vCPU mapping for faster MSI injection
BillXiang
xiangwencheng at lanxincomputing.com
Wed Oct 7 23:41:39 PDT 2026
On 10/2/2026 2:53 PM, Anup Patel wrote:
> 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.
Hi Anup,
Thanks for the review. You’re right — hart_index is not guaranteed
contiguous because it comes from the userspace-provided IMSIC address.
Sizing the table by created_vcpus and bounds-checking against it is
therefore wrong.
I'll use an xarray keyed by hart_index instead, or drop the optimization
if that’s preferred.
Regards,
Bill
>
> 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
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