Re: [PATCH] vfio/iova_bitmap: refactor iova_bitmap_set() to better handle page boundaries

[Jason Gunthorpe <jgg@nvidia.com>]

On Fri, Nov 25, 2022 at 05:29:56PM +0000, Joao Martins wrote:
> Commit f38044e5ef58 ("vfio/iova_bitmap: Fix PAGE_SIZE unaligned bitmaps")
> had fixed the unaligned bitmaps by capping the remaining iterable set at
> the start of the bitmap. Although, that mistakenly worked around
> iova_bitmap_set() incorrectly setting bits across page boundary.
> 
> Fix this by reworking the loop inside iova_bitmap_set() to iterate over a
> range of bits to set (cur_bit .. last_bit) which may span different pinned
> pages, thus updating @page_idx and @offset as it sets the bits. The
> previous cap to the first page is now adjusted to be always accounted
> rather than when there's only a non-zero pgoff.
> 
> While at it, make @page_idx , @offset and @nbits to be unsigned int given
> that it won't be more than 512 and 4096 respectively (even a bigger
> PAGE_SIZE or a smaller struct page size won't make this bigger than the
> above 32-bit max). Also, delete the stale kdoc on Return type.
> 
> Cc: Avihai Horon <avihaih@nvidia.com>
> Co-developed-by: Jason Gunthorpe <jgg@nvidia.com>
> Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
> Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
> ---
> It passes my tests but to be extra sure: Avihai could you take this
> patch a spin in your rig/tests as well? Thanks!
> ---
>  drivers/vfio/iova_bitmap.c | 30 +++++++++++++-----------------
>  1 file changed, 13 insertions(+), 17 deletions(-)

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

Jason