Hi Stefan,
> On Sep 28, 2026, at 14:06, Stefan Butz via <[email protected]> wrote:
>
> The number of interrupt identities supported by the host's KVM AIA
> is limited. On Spacemit K3 and Tenstorrent Atlantis to 63.
> virt machine alwayas aks for 255 identities, so it fails if on those
> platforms.
>
> Read and apply host limit from KVM AIA device and apply.
>
> Resolves: https://gitlab.com/qemu-project/qemu/-/work_items/4599
>
> Signed-off-by: Stefan Butz <[email protected]>
> ---
> hw/riscv/virt.c | 12 +++++++++++-
> target/riscv/kvm/kvm-cpu.c | 16 ++++++++++++++++
> target/riscv/kvm/kvm-stub.c | 5 +++++
> target/riscv/kvm/kvm_riscv.h | 1 +
> 4 files changed, 33 insertions(+), 1 deletion(-)
>
> diff --git a/hw/riscv/virt.c b/hw/riscv/virt.c
> index 28fa31d538..2af85ec5c3 100644
> --- a/hw/riscv/virt.c
> +++ b/hw/riscv/virt.c
> @@ -78,6 +78,16 @@ static bool virt_use_emulated_aplic(RISCVVirtAIAType
> aia_type)
> return riscv_use_emulated_aplic(msimode);
> }
>
> +static void virt_kvm_aia_create(RISCVVirtState *s)
> +{
> + kvm_riscv_aia_create();
> +
> + s->num_msis = MIN(s->num_msis, kvm_riscv_aia_get_num_ids());
The host may support more than 255 guest interrupt identities, but
this MIN() keeps num_msis capped at the default value of 255.
Is this intentional to preserve the existing default? Would it make
sense to allow users to configure a higher value when the host
supports it?
> + if (!virt_use_emulated_aplic(s->aia_type)) {
> + s->num_sources = MIN(s->num_sources, s->num_msis);
The value of num_sources has been modified here, while the value of
aplic_props.irqchip_num_sources set in create_fdt_sockets still uses
the default hard-coded value.
> + }
> +}
> +
> static bool virt_aclint_allowed(void)
> {
> return tcg_enabled() || qtest_enabled();
> @@ -734,7 +744,7 @@ static void virt_machine_init(MachineState *machine)
> }
>
> if (kvm_enabled() && virt_use_kvm_aia_aplic_imsic(s->aia_type)) {
> - kvm_riscv_aia_create();
> + virt_kvm_aia_create(s);
> }
>
> /* Initialize sockets */
> diff --git a/target/riscv/kvm/kvm-cpu.c b/target/riscv/kvm/kvm-cpu.c
> index 1098581e7a..0409af3255 100644
> --- a/target/riscv/kvm/kvm-cpu.c
> +++ b/target/riscv/kvm/kvm-cpu.c
> @@ -1870,6 +1870,22 @@ void kvm_riscv_aia_create(void)
> }
> }
>
> +uint64_t kvm_riscv_aia_get_num_ids(void)
> +{
> + uint64_t num_ids;
> + int ret;
> +
> + ret = kvm_device_access(aia_fd, KVM_DEV_RISCV_AIA_GRP_CONFIG,
> + KVM_DEV_RISCV_AIA_CONFIG_IDS,
> + &num_ids, false, NULL);
The KVM CONFIG_IDS GET attribute writes a u32, so num_ids should
be uint32_t. With the current uint64_t variable, the upper 32 bits
remain uninitialized and may affect the MIN() result.
The return type, declaration, and non-KVM stub should also be
updated accordingly.
> + if (ret < 0) {
> + error_report("KVM AIA: failed to get number of msi");
> + exit(1);
> + }
> +
> + return num_ids;
> +}
> +
> void kvm_riscv_aia_init(MachineState *machine, uint64_t group_shift,
> uint64_t aia_irq_num, uint64_t aia_msi_num,
> uint64_t aplic_base, uint64_t imsic_base,
> diff --git a/target/riscv/kvm/kvm-stub.c b/target/riscv/kvm/kvm-stub.c
> index 672f635b08..f5f5418b3c 100644
> --- a/target/riscv/kvm/kvm-stub.c
> +++ b/target/riscv/kvm/kvm-stub.c
> @@ -14,6 +14,11 @@ void kvm_riscv_aia_create(void)
> g_assert_not_reached();
> }
>
> +uint64_t kvm_riscv_aia_get_num_ids(void)
> +{
> + g_assert_not_reached();
> +}
> +
> void kvm_riscv_aia_init(MachineState *machine, uint64_t group_shift,
> uint64_t aia_irq_num, uint64_t aia_msi_num,
> uint64_t aplic_base, uint64_t imsic_base,
> diff --git a/target/riscv/kvm/kvm_riscv.h b/target/riscv/kvm/kvm_riscv.h
> index 532e42b0df..d8ae73fa1e 100644
> --- a/target/riscv/kvm/kvm_riscv.h
> +++ b/target/riscv/kvm/kvm_riscv.h
> @@ -24,6 +24,7 @@
> void kvm_riscv_reset_vcpu(RISCVCPU *cpu);
> void kvm_riscv_set_irq(RISCVCPU *cpu, int irq, int level);
> void kvm_riscv_aia_create(void);
> +uint64_t kvm_riscv_aia_get_num_ids(void);
> void kvm_riscv_aia_init(MachineState *machine, uint64_t group_shift,
> uint64_t aia_irq_num, uint64_t aia_msi_num,
> uint64_t aplic_base, uint64_t imsic_base,
>
> --
> Git-157)
>
Best regards,
Qingwei Hu
