[PATCH v3] irqchip/riscv-imsic: Adjust the number of available guest irq files

[Anup Patel]

On Sat, Dec 20, 2025 at 10:07 PM Xu Lu <luxu.kernel at bytedance.com> wrote:
>
> During initialization, kernel maps the MMIO resources of IMSIC, which is
> parsed from ACPI or DTS and may not strictly contains all guest
> interrupt files. Page fault happens when KVM wrongly allocates an
> unmapped guest interrupt file and writes it.

The motivation is not clear from the above text and needs to improve.

How about the following ?

Currently, KVM assumes the minimum of implemented HGEIE bits and
"BIT(gc->guest_index_bits) - 1" as the number of guest files available
across all CPUs. This will not work only when CPUs have different number
of guest files because KVM may incorrectly allocate a guest file on a CPU
with fewer guest files.

>
> Thus, during initialization, we calculate the number of available guest

s/Thus, during initialization/To address the above/

> interrupt files according to MMIO resources and constrain the number of
> guest interrupt files that can be allocated by KVM.
>
> Signed-off-by: Xu Lu <luxu.kernel at bytedance.com>
> ---
>  arch/riscv/kvm/aia.c                    | 2 +-
>  drivers/irqchip/irq-riscv-imsic-state.c | 7 ++++++-
>  include/linux/irqchip/riscv-imsic.h     | 3 +++
>  3 files changed, 10 insertions(+), 2 deletions(-)
>
> diff --git a/arch/riscv/kvm/aia.c b/arch/riscv/kvm/aia.c
> index dad3181856600..cac3c2b51d724 100644
> --- a/arch/riscv/kvm/aia.c
> +++ b/arch/riscv/kvm/aia.c
> @@ -630,7 +630,7 @@ int kvm_riscv_aia_init(void)
>          */
>         if (gc)
>                 kvm_riscv_aia_nr_hgei = min((ulong)kvm_riscv_aia_nr_hgei,
> -                                           BIT(gc->guest_index_bits) - 1);
> +                                           gc->nr_guest_files);
>         else
>                 kvm_riscv_aia_nr_hgei = 0;
>
> diff --git a/drivers/irqchip/irq-riscv-imsic-state.c b/drivers/irqchip/irq-riscv-imsic-state.c
> index dc95ad856d80a..1e982ce024a47 100644
> --- a/drivers/irqchip/irq-riscv-imsic-state.c
> +++ b/drivers/irqchip/irq-riscv-imsic-state.c
> @@ -794,7 +794,7 @@ static int __init imsic_parse_fwnode(struct fwnode_handle *fwnode,
>
>  int __init imsic_setup_state(struct fwnode_handle *fwnode, void *opaque)
>  {
> -       u32 i, j, index, nr_parent_irqs, nr_mmios, nr_handlers = 0;
> +       u32 i, j, index, nr_parent_irqs, nr_mmios, nr_guest_files, nr_handlers = 0;
>         struct imsic_global_config *global;
>         struct imsic_local_config *local;
>         void __iomem **mmios_va = NULL;
> @@ -888,6 +888,7 @@ int __init imsic_setup_state(struct fwnode_handle *fwnode, void *opaque)
>         }
>
>         /* Configure handlers for target CPUs */
> +       global->nr_guest_files = BIT(global->guest_index_bits) - 1;
>         for (i = 0; i < nr_parent_irqs; i++) {
>                 rc = imsic_get_parent_hartid(fwnode, i, &hartid);
>                 if (rc) {
> @@ -928,6 +929,10 @@ int __init imsic_setup_state(struct fwnode_handle *fwnode, void *opaque)
>                 local->msi_pa = mmios[index].start + reloff;
>                 local->msi_va = mmios_va[index] + reloff;
>

Need comments explaining why we are taking the
minimum number of guest files across CPUs.

> +               nr_guest_files = (resource_size(&mmios[index]) - reloff) / IMSIC_MMIO_PAGE_SZ - 1;
> +               global->nr_guest_files = global->nr_guest_files > nr_guest_files ? nr_guest_files :
> +                                        global->nr_guest_files;

global->nr_guest_files = min(nr_guest_files, global->nr_guest_files);

> +
>                 nr_handlers++;
>         }
>
> diff --git a/include/linux/irqchip/riscv-imsic.h b/include/linux/irqchip/riscv-imsic.h
> index 7494952c55187..43aed52385008 100644
> --- a/include/linux/irqchip/riscv-imsic.h
> +++ b/include/linux/irqchip/riscv-imsic.h
> @@ -69,6 +69,9 @@ struct imsic_global_config {
>         /* Number of guest interrupt identities */
>         u32                                     nr_guest_ids;
>
> +       /* Number of guest interrupt files per core */
> +       u32                                     nr_guest_files;
> +
>         /* Per-CPU IMSIC addresses */
>         struct imsic_local_config __percpu      *local;
>  };
> --
> 2.20.1
>

Regards,
Anup