Subject: Re: [PATCH v2 03/39] irqchip/gic-v5: Setup gic_kvm_info on ACPI hosts

From: Marc Zyngier <[email-masked]>
Date: Wed, 27 May 2026 11:51:53 +0100

On Thu, 21 May 2026 15:50:09 +0100,
Sascha Bischoff <[email-masked]> wrote:
> 
> Device-tree based GICv5 probing already passes the IRS details and
> maintenance interrupt to KVM, but the ACPI path only initialises the
> irqchip and installs the ACPI IRQ model. As a result, KVM never sees
> the GICv5 host information required to probe the vGIC on ACPI systems.
> 
> Add the ACPI equivalent of the DT KVM setup. Parse the MADT GICC
> entries for the maintenance interrupt, require all relevant entries to
> agree, register the interrupt as a GICv5 PPI-encoded GSI, and pass the
> resulting IRQ together with the IRS base and coherency information to
> KVM. Native GICv5 does not require a maintenance interrupt unless the
> legacy GICv3-compatible CPU interface is present, so preserve the
> existing no-maintenance-IRQ handling for that case.
> 
> Signed-off-by: Sascha Bischoff <[email-masked]>
> ---
>  drivers/irqchip/irq-gic-v5.c | 103 +++++++++++++++++++++++++++++++++--
>  1 file changed, 98 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/irqchip/irq-gic-v5.c b/drivers/irqchip/irq-gic-v5.c
> index 707deabbf2f63..ccd1ec69a6ab2 100644
> --- a/drivers/irqchip/irq-gic-v5.c
> +++ b/drivers/irqchip/irq-gic-v5.c
> @@ -1126,7 +1126,7 @@ static void gicv5_set_cpuif_idbits(void)
>  #ifdef CONFIG_KVM
>  static struct gic_kvm_info gic_v5_kvm_info __initdata;
>  
> -static void __init gic_of_setup_kvm_info(struct device_node *node)
> +static void __init gic_setup_kvm_info(unsigned int maint_irq)
>  {
>  	struct gicv5_irs_chip_data *irs_data = gicv5_irs_get_chip_data();
>  
> @@ -1140,13 +1140,14 @@ static void __init gic_of_setup_kvm_info(struct device_node *node)
>  		return;
>  	}
>  
> -	gic_v5_kvm_info.type = GIC_V5;
> +	if (WARN_ON(!irs_data))
> +		return;
>  
> +	gic_v5_kvm_info.type = GIC_V5;
>  	gic_v5_kvm_info.gicv5_irs.base = irs_data->irs_base;
>  	gic_v5_kvm_info.gicv5_irs.non_coherent = !!(irs_data->flags & IRS_FLAGS_NON_COHERENT);
> -
> -	/* GIC Virtual CPU interface maintenance interrupt */
> -	gic_v5_kvm_info.maint_irq = irq_of_parse_and_map(node, 0);
> +	gic_v5_kvm_info.maint_irq = maint_irq;
> +	gic_v5_kvm_info.no_maint_irq_mask = false;

You remove this last line from patch #1, and reintroduce it here. My
gut feeling is that it should never be removed the first place.

>
>  	/*
>  	 * We require an MI if we have legacy support, but don't, otherwise.
> @@ -1162,10 +1163,101 @@ static void __init gic_of_setup_kvm_info(struct device_node *node)
>  
>  	vgic_set_kvm_info(&gic_v5_kvm_info);
>  }
> +
> +static void __init gic_of_setup_kvm_info(struct device_node *node)
> +{
> +	/* GIC Virtual CPU interface maintenance interrupt */
> +	gic_setup_kvm_info(irq_of_parse_and_map(node, 0));
> +}
> +
> +#ifdef CONFIG_ACPI
> +struct gicv5_acpi_kvm_info {
> +	u32 maint_irq;
> +	int maint_irq_mode;
> +};
> +
> +static struct gicv5_acpi_kvm_info acpi_v5_kvm_info __initdata;
> +
> +static int __init gic_acpi_parse_virt_madt_gicc(union acpi_subtable_headers *header,
> +						const unsigned long end)
> +{
> +	struct acpi_madt_generic_interrupt *gicc =
> +		(struct acpi_madt_generic_interrupt *)header;
> +	static int first_madt = true;
> +	int maint_irq_mode;
> +
> +	if (!(gicc->flags &
> +	      (ACPI_MADT_ENABLED | ACPI_MADT_GICC_ONLINE_CAPABLE)))
> +		return 0;
> +
> +	maint_irq_mode = (gicc->flags & ACPI_MADT_VGIC_IRQ_MODE) ?
> +			 ACPI_EDGE_SENSITIVE : ACPI_LEVEL_SENSITIVE;
> +
> +	if (first_madt) {
> +		first_madt = false;
> +
> +		acpi_v5_kvm_info.maint_irq = gicc->vgic_interrupt;
> +		acpi_v5_kvm_info.maint_irq_mode = maint_irq_mode;
> +		return 0;
> +	}
> +
> +	/* The maintenance interrupt must be the same for every GICC entry. */
> +	if (acpi_v5_kvm_info.maint_irq != gicc->vgic_interrupt ||
> +	    acpi_v5_kvm_info.maint_irq_mode != maint_irq_mode)
> +		return -EINVAL;
> +
> +	return 0;
> +}
> +
> +static bool __init gic_acpi_collect_virt_info(void)
> +{
> +	int count;
> +
> +	acpi_v5_kvm_info.maint_irq = 0;
> +	acpi_v5_kvm_info.maint_irq_mode = 0;
> +
> +	count = acpi_table_parse_madt(ACPI_MADT_TYPE_GENERIC_INTERRUPT,
> +				      gic_acpi_parse_virt_madt_gicc, 0);
> +
> +	return count > 0;
> +}
> +
> +static void __init gic_acpi_setup_kvm_info(void)
> +{
> +	unsigned int maint_irq = 0;
> +	int irq;
> +
> +	if (!gic_acpi_collect_virt_info()) {
> +		pr_warn("Unable to get hardware information used for virtualization\n");
> +		return;
> +	}
> +
> +	if (acpi_v5_kvm_info.maint_irq) {
> +		u32 gsi = FIELD_PREP(GICV5_HWIRQ_TYPE, GICV5_HWIRQ_TYPE_PPI) |
> +			  FIELD_PREP(GICV5_HWIRQ_ID, acpi_v5_kvm_info.maint_irq);
> +
> +		irq = acpi_register_gsi(NULL, gsi,
> +					acpi_v5_kvm_info.maint_irq_mode,
> +					ACPI_ACTIVE_HIGH);
> +		if (irq <= 0)
> +			return;

This probably deserves a bit of a warning. And maybe not completely
fail the registration with KVM?

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.