Virtualization - Oct 2023 - [PATCH v2] virtio_pci: Switch away from deprecated irq_set_affinity_hint

On Wed, Oct 25, 2023 at 04:53 PM +02, Jakub Sitnicki
wrote:
> Since commit 65c7cdedeb30 ("genirq: Provide new interfaces for
affinity
> hints") irq_set_affinity_hint is being phased out.
>
> Switch to new interfaces for setting and applying irq affinity hints.
>
> Signed-off-by: Jakub Sitnicki <jakub at cloudflare.com>
> ---
> v2:
>  - Leave cpumask_copy as is. We can't pass pointer to stack memory as
hint.
>    Proposed a change to IRQ affinity interface to address this limitation:
>    https://lore.kernel.org/r/20231025141517.375378-1-jakub at
cloudflare.com
Just a note to the ^ - if we wanted to get rid of msix_affinity_masks,
we could call irq_set_affinity directly, instead of calling it through
irq_set_affinity[_and]_hint.

The hint wouldn't be available any more in /proc/irq/N/affinity_hint,
but the same information can be gathered from /proc/irq/N/smp_affinity.

[...]

On Thu, Oct 26, 2023 at 06:25:08PM +0200, Jakub Sitnicki
wrote:
> On Wed, Oct 25, 2023 at 04:53 PM +02, Jakub Sitnicki wrote:
> > Since commit 65c7cdedeb30 ("genirq: Provide new interfaces for
affinity
> > hints") irq_set_affinity_hint is being phased out.
> >
> > Switch to new interfaces for setting and applying irq affinity hints.
> >
> > Signed-off-by: Jakub Sitnicki <jakub at cloudflare.com>
> > ---
> > v2:
> >  - Leave cpumask_copy as is. We can't pass pointer to stack memory
as hint.
> >    Proposed a change to IRQ affinity interface to address this
limitation:
> >    https://lore.kernel.org/r/20231025141517.375378-1-jakub at
cloudflare.com
> 
> Just a note to the ^ - if we wanted to get rid of msix_affinity_masks,
> we could call irq_set_affinity directly, instead of calling it through
> irq_set_affinity[_and]_hint.
> 
> The hint wouldn't be available any more in /proc/irq/N/affinity_hint,
> but the same information can be gathered from /proc/irq/N/smp_affinity.
> 
> [...]

So we are potentially breaking some userspace - what's the value we
gain?  Is there some way we can make disable_irq/enable_irq work?
That would have a lot of value.
There is an actual need for that in virtio for coco but we can't use
these APIs with affinity managed IRQs.

-- 
MST