Re: [Xen-devel] [PATCH] xen/events: Always allocate legacy interrupts on PV guests

[Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>]

Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx> 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@xxxxxxxxxx>
> Suggested-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> ---
>  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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