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

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Message-ID: <CAPYmKFuNB_iKGtXN815WZvZ5zz8-=NcaLrL0uqS9U4snVZPaTA@mail.gmail.com>
Date: Mon, 22 Dec 2025 16:54:37 +0800
From: Xu Lu <luxu.kernel@...edance.com>
To: Anup Patel <anup@...infault.org>
Cc: atish.patra@...ux.dev, pjw@...nel.org, palmer@...belt.com, 
	aou@...s.berkeley.edu, alex@...ti.fr, tglx@...utronix.de, kvm@...r.kernel.org, 
	kvm-riscv@...ts.infradead.org, linux-riscv@...ts.infradead.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [External] Re: [PATCH v3] irqchip/riscv-imsic: Adjust the number
 of available guest irq files

Roger that!

On Mon, Dec 22, 2025 at 1:04 PM Anup Patel <anup@...infault.org> wrote:
>
> On Sat, Dec 20, 2025 at 10:07 PM Xu Lu <luxu.kernel@...edance.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@...edance.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