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

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Message-ID:
 <KUZPR04MB9265AF1883CAE0BDDB8A204DF3B5A@KUZPR04MB9265.apcprd04.prod.outlook.com>
Date: Tue, 23 Dec 2025 14:15:48 +0800
From: "Nutty.Liu" <nutty.liu@...mail.com>
To: Xu Lu <luxu.kernel@...edance.com>, anup@...infault.org,
 atish.patra@...ux.dev, pjw@...nel.org, palmer@...belt.com,
 aou@...s.berkeley.edu, alex@...ti.fr, tglx@...utronix.de
Cc: kvm@...r.kernel.org, kvm-riscv@...ts.infradead.org,
 linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4] irqchip/riscv-imsic: Adjust the number of available
 guest irq files


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@...edance.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@...mail.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;
>   };