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SubjectRe: [Xen-devel] [PATCH] xen/events: Always allocate legacy interrupts on PV guests
Date
Boris Ostrovsky <boris.ostrovsky@oracle.com> writes:

> After commit 8c058b0b9c34 ("x86/irq: Probe for PIC presence before
> allocating descs for legacy IRQs") early_irq_init() will no longer
> preallocate descriptors for legacy interrupts if PIT does not
> exist.

PIC?

>
> Therefore we need to allocate those descriptors for PV guests
> ourselves.
>
> Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
> Suggested-by: Thomas Gleixner <tglx@linutronix.de>
> ---
> drivers/xen/events/events_base.c | 8 ++++----
> 1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/xen/events/events_base.c b/drivers/xen/events/events_base.c
> index 849500e..a2bb333 100644
> --- a/drivers/xen/events/events_base.c
> +++ b/drivers/xen/events/events_base.c
> @@ -419,8 +419,8 @@ static int __must_check xen_allocate_irq_gsi(unsigned gsi)
> if (xen_pv_domain() && !xen_initial_domain())
> return xen_allocate_irq_dynamic();
>
> - /* Legacy IRQ descriptors are already allocated by the arch. */
> - if (gsi < NR_IRQS_LEGACY)
> + /* On HVM legacy IRQ descriptors are already allocated by the arch. */
> + if (xen_hvm_domain() && gsi < NR_IRQS_LEGACY)
> irq = gsi;

Wouldn't it be better to write it as
if (gsi < nr_legacy_irqs()) ?

I think it's possible to have PIC-less HVM guests in future (btw, what
about HVMlite?). I see nr_legacy_irqs() is x86-only but it can easily be
defined to NR_IRQS_LEGACY on other arches.

> else
> irq = irq_alloc_desc_at(gsi, -1);
> @@ -445,8 +445,8 @@ static void xen_free_irq(unsigned irq)
>
> kfree(info);
>
> - /* Legacy IRQ descriptors are managed by the arch. */
> - if (irq < NR_IRQS_LEGACY)
> + /* On HVM legacy IRQ descriptors are managed by the arch. */
> + if (xen_hvm_domain() && irq < NR_IRQS_LEGACY)
> return;
>
> irq_free_desc(irq);

--
Vitaly


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