RE: [PATCH V4 06/11] vfio/pci: Remove interrupt context counter

[Tian, Kevin]

> From: Chatre, Reinette <reinette.chatre@xxxxxxxxx>
> Sent: Friday, April 28, 2023 1:36 AM
> 
> struct vfio_pci_core_device::num_ctx counts how many interrupt
> contexts have been allocated. When all interrupt contexts are
> allocated simultaneously num_ctx provides the upper bound of all
> vectors that can be used as indices into the interrupt context
> array.
> 
> With the upcoming support for dynamic MSI-X the number of
> interrupt contexts does not necessarily span the range of allocated
> interrupts. Consequently, num_ctx is no longer a trusted upper bound
> for valid indices.
> 
> Stop using num_ctx to determine if a provided vector is valid. Use
> the existence of allocated interrupt.
> 
> This changes behavior on the error path when user space provides
> an invalid vector range. Behavior changes from early exit without
> any modifications to possible modifications to valid vectors within
> the invalid range. This is acceptable considering that an invalid
> range is not a valid scenario, see link to discussion.
> 
> The checks that ensure that user space provides a range of vectors
> that is valid for the device are untouched.
> 
> Signed-off-by: Reinette Chatre <reinette.chatre@xxxxxxxxx>

Reviewed-by: Kevin Tian <kevin.tian@xxxxxxxxx>