Re: [PATCH V4] xen: privcmd: Add support for irqfd

[Viresh Kumar <viresh.kumar@xxxxxxxxxx>]

On 25-07-23, 16:27, Viresh Kumar wrote:
> Xen provides support for injecting interrupts to the guests via the
> HYPERVISOR_dm_op() hypercall. The same is used by the Virtio based
> device backend implementations, in an inefficient manner currently.
> 
> Generally, the Virtio backends are implemented to work with the Eventfd
> based mechanism. In order to make such backends work with Xen, another
> software layer needs to poll the Eventfds and raise an interrupt to the
> guest using the Xen based mechanism. This results in an extra context
> switch.
> 
> This is not a new problem in Linux though. It is present with other
> hypervisors like KVM, etc. as well. The generic solution implemented in
> the kernel for them is to provide an IOCTL call to pass the interrupt
> details and eventfd, which lets the kernel take care of polling the
> eventfd and raising of the interrupt, instead of handling this in user
> space (which involves an extra context switch).
> 
> This patch adds support to inject a specific interrupt to guest using
> the eventfd mechanism, by preventing the extra context switch.
> 
> Inspired by existing implementations for KVM, etc..
> 
> Signed-off-by: Viresh Kumar <viresh.kumar@xxxxxxxxxx>
> ---
> V3->V4
> - Drop the imported definitions to hvm/dm_op.h.
> - Make the caller pass a pointer to pre-filled "struct xen_dm_op" instance and
>   get rid of irq and level fields.
> - Enable the irqfd feature under a new Kconfig entry.

Ping.

-- 
viresh