Re: [PATCH v4 3/6] iommufd: Iterate the cache invalidation array in the core

[Jason Gunthorpe <jgg@nvidia.com>]

On Tue, Jul 14, 2026 at 11:48:49AM -0700, Nicolin Chen wrote:
> The cache invalidation ops, cache_invalidate_user() for a nested HWPT and
> the cache_invalidate() for a vIOMMU, are each handed the full user request
> array and report how many of the array entries they handled by setting the
> array->entry_num. Every driver therefore implements its own loop over the
> array, and a driver wanting to process that array in fixed-size chunks
> (e.g. to issue commands out of a fixed-size on-stack buffer) has to carry
> the loop and its sub-array bookkeeping all on its own.
> 
> Move the iteration into the iommufd core instead. Invoke the op with a
> sub-array that starts at the first not-yet-handled entry, let it handle a
> prefix of that sub-array and report the count via array->entry_num, then
> advance the base pointer and re-invoke the op until the entire array has
> been consumed or until the op returns an error along the way.
> 
> A driver that handles the entire window in one single call, as all of the
> current drivers happen to do, finishes the loop in just one pass, so this
> does not change any of the existing behavior. It instead lets each of the
> drivers convert to bounded chunk processing on its own, done by each of the
> subsequent changes.
> 
> Suggested-by: Jason Gunthorpe <jgg@nvidia.com>
> Reviewed-by: Kevin Tian <kevin.tian@intel.com>
> Reviewed-by: Lu Baolu <baolu.lu@linux.intel.com>
> Reviewed-by: Pranjal Shrivastava <praan@google.com>
> Assisted-by: Claude:claude-opus-4-8
> Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
> ---
>  include/linux/iommu.h                |  6 ++++--
>  include/linux/iommufd.h              |  2 ++
>  drivers/iommu/iommufd/hw_pagetable.c | 25 +++++++++++++++----------
>  3 files changed, 21 insertions(+), 12 deletions(-)

Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>

Jason