Re: [PATCH kvmtool v3 3/6] arm64: nested: add support for setting maintenance IRQ

Andre Przywara
2025-09-16T12:16:40Z

On Mon, 4 Aug 2025 15:43:09 +0100
Alexandru Elisei <alexandru.elisei@arm.com> wrote:

Hi Alex,

> Hi Andre,
>
> 'add' should be capitalized.
>
> On Tue, Jul 29, 2025 at 10:57:42AM +0100, Andre Przywara wrote:
> > Uses the new VGIC KVM device attribute to set the maintenance IRQ.
> > This is fixed to use PPI 9, as a platform decision made by kvmtool,
> > matching the SBSA recommendation.
> >
> > Signed-off-by: Andre Przywara <andre.przywara@arm.com>
> > ---
> > arm64/arm-cpu.c | 3 ++-
> > arm64/gic.c | 21 ++++++++++++++++++++-
> > arm64/include/kvm/gic.h | 2 +-
> > 3 files changed, 23 insertions(+), 3 deletions(-)
> >
> > diff --git a/arm64/arm-cpu.c b/arm64/arm-cpu.c
> > index 69bb2cb2c..1e456f2c6 100644
> > --- a/arm64/arm-cpu.c
> > +++ b/arm64/arm-cpu.c
> > @@ -14,7 +14,8 @@ static void generate_fdt_nodes(void *fdt, struct kvm *kvm)
> > {
> > int timer_interrupts[4] = {13, 14, 11, 10};
> >
> > - gic__generate_fdt_nodes(fdt, kvm->cfg.arch.irqchip);
> > + gic__generate_fdt_nodes(fdt, kvm->cfg.arch.irqchip,
> > + kvm->cfg.arch.nested_virt);
> > timer__generate_fdt_nodes(fdt, kvm, timer_interrupts);
> > pmu__generate_fdt_nodes(fdt, kvm);
> > }
> > diff --git a/arm64/gic.c b/arm64/gic.c
> > index b0d3a1abb..7461b0f3f 100644
> > --- a/arm64/gic.c
> > +++ b/arm64/gic.c
> > @@ -11,6 +11,8 @@
> >
> > #define IRQCHIP_GIC 0
> >
> > +#define GIC_MAINT_IRQ 9
> > +
> > static int gic_fd = -1;
> > static u64 gic_redists_base;
> > static u64 gic_redists_size;
> > @@ -302,10 +304,15 @@ static int gic__init_gic(struct kvm *kvm)
> >
> > int lines = irq__get_nr_allocated_lines();
> > u32 nr_irqs = ALIGN(lines, 32) + GIC_SPI_IRQ_BASE;
> > + u32 maint_irq = GIC_MAINT_IRQ + 16; /* PPI */
>
> There's already a define for PPIs:
>
> u32 maint_irq = GIC_PPI_IRQ_BASE + GIC_MAINT_IRQ;

Indeed, will use that.

> > struct kvm_device_attr nr_irqs_attr = {
> > .group = KVM_DEV_ARM_VGIC_GRP_NR_IRQS,
> > .addr = (u64)(unsigned long)&nr_irqs,
> > };
> > + struct kvm_device_attr maint_irq_attr = {
> > + .group = KVM_DEV_ARM_VGIC_GRP_MAINT_IRQ,
> > + .addr = (u64)(unsigned long)&maint_irq,
> > + };
> > struct kvm_device_attr vgic_init_attr = {
> > .group = KVM_DEV_ARM_VGIC_GRP_CTRL,
> > .attr = KVM_DEV_ARM_VGIC_CTRL_INIT,
> > @@ -325,6 +332,13 @@ static int gic__init_gic(struct kvm *kvm)
> > return ret;
> > }
> >
> > + if (kvm->cfg.arch.nested_virt &&
> > + !ioctl(gic_fd, KVM_HAS_DEVICE_ATTR, &maint_irq_attr)) {
>
> I'm not sure how useful the HAS_DEVICE_ATTR call is here: kvm_cpu__arch_init(),
> which checks for KVM_CAP_ARM_EL2 capability, is called before gic__init_gic()
> (base_init() vs late_init()). So at this point we know that KVM supports nested
> virtualization.
>
> Was it that KVM at some point supported nested virtualization but didn't have
> the KVM_DEV_ARM_VGIC_GRP_MAINT_IRQ device attribute implemented? And if that was
> the case, do we want to support that version of KVM in kvmtool?

I am on Marc's side here: we should stick to the clear pattern of checking
for that particular feature before we use it, and not rely on some
implementation detail.

> > + ret = ioctl(gic_fd, KVM_SET_DEVICE_ATTR, &maint_irq_attr);
> > + if (ret)
> > + return ret;
> > + }
> > +
> > irq__routing_init(kvm);
> >
> > if (!ioctl(gic_fd, KVM_HAS_DEVICE_ATTR, &vgic_init_attr)) {
> > @@ -342,7 +356,7 @@ static int gic__init_gic(struct kvm *kvm)
> > }
> > late_init(gic__init_gic)
> >
> > -void gic__generate_fdt_nodes(void *fdt, enum irqchip_type type)
> > +void gic__generate_fdt_nodes(void *fdt, enum irqchip_type type, bool nested)
>
> I think you can drop 'type' and 'nested' and pass kvm directly, see below why.

Ah, yes, makes sense, thanks!

> > {
> > const char *compatible, *msi_compatible = NULL;
> > u64 msi_prop[2];
> > @@ -350,6 +364,8 @@ void gic__generate_fdt_nodes(void *fdt, enum irqchip_type type)
> > cpu_to_fdt64(ARM_GIC_DIST_BASE), cpu_to_fdt64(ARM_GIC_DIST_SIZE),
> > 0, 0, /* to be filled */
> > };
> > + u32 maint_irq[3] = {cpu_to_fdt32(1), cpu_to_fdt32(GIC_MAINT_IRQ),
> ^
> You can leave that empty for the compiler to figure it out, like for the
> 'reg_prop' local variable.
>
> Also, there's a define to specify the IRQ type, it's GIC_FDT_IRQ_TYPE_PPI, you
> might want to use that.
>
> > + cpu_to_fdt32(0xff04)};
> ^^^^^^
> I think gic__get_fdt_irq_cpumask(kvm) | IRQ_TYPE_LEVEL_HIGH is better, similar
> to pmu.c and timer.c.

Yes, better, fixed.

> >
> > switch (type) {
> > case IRQCHIP_GICV2M:
> > @@ -377,6 +393,9 @@ void gic__generate_fdt_nodes(void *fdt, enum irqchip_type type)
> > _FDT(fdt_property_cell(fdt, "#interrupt-cells", GIC_FDT_IRQ_NUM_CELLS));
> > _FDT(fdt_property(fdt, "interrupt-controller", NULL, 0));
> > _FDT(fdt_property(fdt, "reg", reg_prop, sizeof(reg_prop)));
> > + if (nested)
> > + _FDT(fdt_property(fdt, "interrupts", maint_irq,
> > + sizeof(maint_irq)));
>
> Braces around the if if statement body? (it's multiline even though it's on
> instruction)

Done.

Cheers,
Andre

>
> Thanks,
> Alex
>
> > _FDT(fdt_property_cell(fdt, "phandle", PHANDLE_GIC));
> > _FDT(fdt_property_cell(fdt, "#address-cells", 2));
> > _FDT(fdt_property_cell(fdt, "#size-cells", 2));
> > diff --git a/arm64/include/kvm/gic.h b/arm64/include/kvm/gic.h
> > index ad8bcbf21..1541a5824 100644
> > --- a/arm64/include/kvm/gic.h
> > +++ b/arm64/include/kvm/gic.h
> > @@ -36,7 +36,7 @@ struct kvm;
> > int gic__alloc_irqnum(void);
> > int gic__create(struct kvm *kvm, enum irqchip_type type);
> > int gic__create_gicv2m_frame(struct kvm *kvm, u64 msi_frame_addr);
> > -void gic__generate_fdt_nodes(void *fdt, enum irqchip_type type);
> > +void gic__generate_fdt_nodes(void *fdt, enum irqchip_type type, bool nested);
> > u32 gic__get_fdt_irq_cpumask(struct kvm *kvm);
> >
> > int gic__add_irqfd(struct kvm *kvm, unsigned int gsi, int trigger_fd,
> > --
> > 2.25.1
> >