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

["BillXiang" <xiangwencheng@lanxincomputing.com>]

On 10/29/2026 5:15 PM, Nutty.Liu wrote:
> 
> 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.

Thanks for the reminder.

>> - 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);