Re: [PATCH v2 08/22] iommufd: Abstract iopt_pin_pages and iopt_unpin_pages helpers

[Nicolin Chen <nicolinc@nvidia.com>]

On Tue, May 06, 2025 at 09:36:38AM +0000, Tian, Kevin wrote:
> > From: Nicolin Chen <nicolinc@nvidia.com>
> > Sent: Saturday, April 26, 2025 1:58 PM
> > 
> > The new vCMDQ object will be added for HW to access the guest memory for
> > a
> > HW-accelerated virtualization feature. It needs to ensure the guest memory
> > pages are pinned when HW accesses them and they are contiguous in
> > physical
> > address space.
> > 
> > This is very like the existing iommufd_access_pin_pages() that outputs the
> > pinned page list for the caller to test its contiguity.
> > 
> > Move those code from iommufd_access_pin/unpin_pages() and related
> > function
> > for a pair of iopt helpers that can be shared with the vCMDQ allocator. As
> > the vCMDQ allocator will be a user-space triggered ioctl function, WARN_ON
> > would not be a good fit in the new iopt_unpin_pages(), thus change them to
> > use WARN_ON_ONCE instead.
> > 
> > Rename check_area_prot() to align with the existing iopt_area helpers, and
> > inline it to the header since iommufd_access_rw() still uses it.
> > 
> > Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
> 
> any reason why this cannot be done by the core? all types of vcmd
> queues need to pin the guest buffer pages, no matter the IOMMU
> accesses GPA or HPA.
> 
> Jason made a similar comment earlier [1]. 
> 
> check of continuity is still done by the driver, if HPA is being accessed.
> 
> [1] https://lore.kernel.org/all/20250424134049.GP1648741@nvidia.com/

But I am doing in the core. I have iopt_pin_pages() called in the
core ioctl handler iommufd_vqueue_alloc_ioctl():

https://lore.kernel.org/linux-iommu/1ef2e242ee1d844f823581a5365823d78c67ec6a.1746139811.git.nicolinc@nvidia.com/

Thanks
Nicolin