[PATCH v4] irqchip/riscv-imsic: Adjust the number of available guest irq files

[PATCH v4] irqchip/riscv-imsic: Adjust the number of available guest irq files

[Xu Lu]

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 when CPUs have different number
of guest files because KVM may incorrectly allocate a guest file on a CPU
with fewer guest files.

To address above, during initialization, we calculate the number of
available guest 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@bytedance.com>
---
 arch/riscv/kvm/aia.c                    |  2 +-
 drivers/irqchip/irq-riscv-imsic-state.c | 12 +++++++++++-
 include/linux/irqchip/riscv-imsic.h     |  3 +++
 3 files changed, 15 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..cccca38983577 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 +929,15 @@ 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;
 
+		/*
+		 * KVM uses global->nr_guest_files to determine the available guest
+		 * interrupt files on each CPU. Take the minimum number of guest
+		 * interrupt files across all CPUs to avoid KVM incorrectly allocatling
+		 * an unexisted or unmapped guest interrupt file on some CPUs.
+		 */
+		nr_guest_files = (resource_size(&mmios[index]) - reloff) / IMSIC_MMIO_PAGE_SZ - 1;
+		global->nr_guest_files = min(global->nr_guest_files, 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

Re: [PATCH v4] irqchip/riscv-imsic: Adjust the number of available guest irq files

[Nutty.Liu]

On 12/22/2025 5:37 PM, Xu Lu wrote:
> 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 when CPUs have different number
> of guest files because KVM may incorrectly allocate a guest file on a CPU
> with fewer guest files.
>
> To address above, during initialization, we calculate the number of
> available guest 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@bytedance.com>
> ---
>   arch/riscv/kvm/aia.c                    |  2 +-
>   drivers/irqchip/irq-riscv-imsic-state.c | 12 +++++++++++-
>   include/linux/irqchip/riscv-imsic.h     |  3 +++
>   3 files changed, 15 insertions(+), 2 deletions(-)
Reviewed-by: Nutty Liu <nutty.liu@hotmail.com>

Thanks,
Nutty
> 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..cccca38983577 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 +929,15 @@ 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;
>   
> +		/*
> +		 * KVM uses global->nr_guest_files to determine the available guest
> +		 * interrupt files on each CPU. Take the minimum number of guest
> +		 * interrupt files across all CPUs to avoid KVM incorrectly allocatling
> +		 * an unexisted or unmapped guest interrupt file on some CPUs.
> +		 */
> +		nr_guest_files = (resource_size(&mmios[index]) - reloff) / IMSIC_MMIO_PAGE_SZ - 1;
> +		global->nr_guest_files = min(global->nr_guest_files, 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;
>   };

Re: [PATCH v4] irqchip/riscv-imsic: Adjust the number of available guest irq files

[Anup Patel]

On Mon, Dec 22, 2025 at 3:07 PM Xu Lu <luxu.kernel@bytedance.com> wrote:
>
> 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 when CPUs have different number
> of guest files because KVM may incorrectly allocate a guest file on a CPU
> with fewer guest files.
>
> To address above, during initialization, we calculate the number of

/, we calculate .../, calculate .../

> available guest 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@bytedance.com>
> ---
>  arch/riscv/kvm/aia.c                    |  2 +-
>  drivers/irqchip/irq-riscv-imsic-state.c | 12 +++++++++++-
>  include/linux/irqchip/riscv-imsic.h     |  3 +++
>  3 files changed, 15 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..cccca38983577 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 +929,15 @@ 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;
>
> +               /*
> +                * KVM uses global->nr_guest_files to determine the available guest
> +                * interrupt files on each CPU. Take the minimum number of guest
> +                * interrupt files across all CPUs to avoid KVM incorrectly allocatling

s/allocatling/allocating/

> +                * an unexisted or unmapped guest interrupt file on some CPUs.
> +                */
> +               nr_guest_files = (resource_size(&mmios[index]) - reloff) / IMSIC_MMIO_PAGE_SZ - 1;
> +               global->nr_guest_files = min(global->nr_guest_files, 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
>

Otherwise, it looks good to me.

Reviewed-by: Anup Patel <anup@brainfault.org>

@tglx, Is it okay to take this through the KVM RISC-V tree
since this change focuses on guest files used by KVM ?

Regards,
Anup

Re: [PATCH v4] irqchip/riscv-imsic: Adjust the number of available guest irq files

[Thomas Gleixner]

On Sun, Jan 04 2026 at 18:46, Anup Patel wrote:
> On Mon, Dec 22, 2025 at 3:07 PM Xu Lu <luxu.kernel@bytedance.com> wrote:
>
> Reviewed-by: Anup Patel <anup@brainfault.org>
>
> @tglx, Is it okay to take this through the KVM RISC-V tree
> since this change focuses on guest files used by KVM ?

Sure, if there are no conflicts against tip irq/drivers.

Acked-by: Thomas Gleixner <tglx@kernel.org>