Hello Fred.

On Mon, Jun 10, 2024 at 12:57:06PM GMT, Fred Griffoul [off-list ref] wrote:

The usual way to configure a device interrupt from userland is to write
the /proc/irq/<irq>/smp_affinity or smp_affinity_list files. When using
vfio to implement a device driver or a virtual machine monitor, this may
not be ideal: the process managing the vfio device interrupts may not be
granted root privilege, for security reasons. Thus it cannot directly
control the interrupt affinity and has to rely on an external command.

External commands something privileged? (I'm curious of an example how
this is setup.)

The affinity argument must be a subset of the process cpuset, otherwise
an error -EPERM is returned.

I'm not sure you want to look at task's cpuset mask for this purposes.

Consider setups without cpuset or a change of (cpuset) mask anytime
during lifetime of the task...

Michal