Re: [PATCH v4 03/48] irqchip/gic-v5: Set up gic_kvm_info on ACPI hosts

[Marc Zyngier <maz@kernel.org>]

On Fri, 24 Jul 2026 11:49:11 +0100,
Sascha Bischoff <Sascha.Bischoff@arm.com> 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 <sascha.bischoff@arm.com>
> ---
>  drivers/irqchip/irq-gic-v5.c | 100 +++++++++++++++++++++++++++++++++--
>  1 file changed, 96 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/irqchip/irq-gic-v5.c b/drivers/irqchip/irq-gic-v5.c
> index e7a7aedcfaf78..0d90675fb319b 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();
>  
> @@ -1137,17 +1137,19 @@ static void __init gic_of_setup_kvm_info(struct device_node *node)
>  	 */
>  	if (!gicv5_global_data.virt_capable) {
>  		pr_info("GIC implementation is not virtualization capable\n");
> -		return;
> +		goto out_dispose_maint_irq;
>  	}
>  
> -	gic_v5_kvm_info.type = GIC_V5;
> +	if (WARN_ON(!irs_data))
> +		goto out_dispose_maint_irq;
>  
> +	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.no_maint_irq_mask = false;
> -	gic_v5_kvm_info.maint_irq = irq_of_parse_and_map(node, 0);
> +	gic_v5_kvm_info.maint_irq = maint_irq;
>  
>  	/*
>  	 * We require an MI if we have legacy support, but don't, otherwise.
> @@ -1162,11 +1164,100 @@ static void __init gic_of_setup_kvm_info(struct device_node *node)
>  		gic_v5_kvm_info.no_maint_irq_mask = true;
>  
>  	vgic_set_kvm_info(&gic_v5_kvm_info);
> +	return;
> +
> +out_dispose_maint_irq:
> +	irq_dispose_mapping(maint_irq);
> +}
> +
> +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;
> +

This looks wrong, as the MI cannot be edge-triggered. This is
cargo-culted from the GICv3 code, which is just as buggy (I'll go and
clean it up).

This should simply be ignored, and the existence of the field shows
how little understanding of the architecture the ACPI zealots have.

> +	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;

Similarly, this second check should be dropped. We're not in the
business of validating ACPI tables. Print a FW_BUG warning if you
want, but that's all that needs doing, and we don't need to screw the
user over the FW's brokenness.

> +
> +	return 0;
> +}
> +
> +static bool __init gic_acpi_collect_virt_info(void)
> +{
> +	int count;
> +
> +	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) {
> +		irq = acpi_register_gsi(NULL, acpi_v5_kvm_info.maint_irq,
> +					acpi_v5_kvm_info.maint_irq_mode,
> +					ACPI_ACTIVE_HIGH);

Just hardcode the trigger mode here.

> +		if (irq > 0)
> +			maint_irq = irq;
> +		else
> +			pr_warn("Failed to register GSI for GICv5 maintenance IRQ\n");
> +	}
> +
> +	gic_setup_kvm_info(maint_irq);
>  }
> +#endif

nit: add '// CONFIG_ACPI' here, for consistency.

>  #else
>  static inline void __init gic_of_setup_kvm_info(struct device_node *node)
>  {
>  }
> +
> +#ifdef CONFIG_ACPI
> +static inline void __init gic_acpi_setup_kvm_info(void)
> +{
> +}
> +#endif
>  #endif // CONFIG_KVM
>  
>  static int __init gicv5_init_common(struct fwnode_handle *parent_domain)
> @@ -1265,6 +1356,7 @@ static int __init gic_acpi_init(union acpi_subtable_headers *header, const unsig
>  		goto out_irs;
>  
>  	acpi_set_irq_model(ACPI_IRQ_MODEL_GIC_V5, gic_v5_get_gsi_domain_id);
> +	gic_acpi_setup_kvm_info();
>  
>  	return 0;
>  

Thanks,

	M.

-- 
Jazz isn't dead. It just smells funny.