[PATCH 6.1 0735/1146] vfio/iova_bitmap: refactor iova_bitmap_set() to better handle page boundaries

Greg Kroah-Hartman
2022-12-28T16:26:20Z

From: Joao Martins <joao.m.martins@oracle.com>

[ Upstream commit b058ea3ab5afea873ab8d976277539ca9e43869a ]

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>
Fixes: f38044e5ef58 ("vfio/iova_bitmap: Fix PAGE_SIZE unaligned bitmaps")
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>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Tested-by: Avihai Horon <avihaih@nvidia.com>
Link: https://lore.kernel.org/r/20221129131235.38880-1-joao.m.martins@oracle.com
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/vfio/iova_bitmap.c | 30 +++++++++++++-----------------
1 file changed, 13 insertions(+), 17 deletions(-)

diff --git a/drivers/vfio/iova_bitmap.c b/drivers/vfio/iova_bitmap.c
index 2dd65f040127..0f19d502f351 100644
--- a/drivers/vfio/iova_bitmap.c
+++ b/drivers/vfio/iova_bitmap.c
@@ -297,9 +297,7 @@ static unsigned long iova_bitmap_mapped_remaining(struct iova_bitmap *bitmap)
{
unsigned long remaining, bytes;

- /* Cap to one page in the first iteration, if PAGE_SIZE unaligned. */
- bytes = !bitmap->mapped.pgoff ? bitmap->mapped.npages << PAGE_SHIFT :
- PAGE_SIZE - bitmap->mapped.pgoff;
+ bytes = (bitmap->mapped.npages << PAGE_SHIFT) - bitmap->mapped.pgoff;

remaining = bitmap->mapped_total_index - bitmap->mapped_base_index;
remaining = min_t(unsigned long, remaining,
@@ -398,29 +396,27 @@ int iova_bitmap_for_each(struct iova_bitmap *bitmap, void *opaque,
* Set the bits corresponding to the range [iova .. iova+length-1] in
* the user bitmap.
*
- * Return: The number of bits set.
*/
void iova_bitmap_set(struct iova_bitmap *bitmap,
unsigned long iova, size_t length)
{
struct iova_bitmap_map *mapped = &bitmap->mapped;
- unsigned long offset = (iova - mapped->iova) >> mapped->pgshift;
- unsigned long nbits = max_t(unsigned long, 1, length >> mapped->pgshift);
- unsigned long page_idx = offset / BITS_PER_PAGE;
- unsigned long page_offset = mapped->pgoff;
- void *kaddr;
-
- offset = offset % BITS_PER_PAGE;
+ unsigned long cur_bit = ((iova - mapped->iova) >>
+ mapped->pgshift) + mapped->pgoff * BITS_PER_BYTE;
+ unsigned long last_bit = (((iova + length - 1) - mapped->iova) >>
+ mapped->pgshift) + mapped->pgoff * BITS_PER_BYTE;

do {
- unsigned long size = min(BITS_PER_PAGE - offset, nbits);
+ unsigned int page_idx = cur_bit / BITS_PER_PAGE;
+ unsigned int offset = cur_bit % BITS_PER_PAGE;
+ unsigned int nbits = min(BITS_PER_PAGE - offset,
+ last_bit - cur_bit + 1);
+ void *kaddr;

kaddr = kmap_local_page(mapped->pages[page_idx]);
- bitmap_set(kaddr + page_offset, offset, size);
+ bitmap_set(kaddr, offset, nbits);
kunmap_local(kaddr);
- page_offset = offset = 0;
- nbits -= size;
- page_idx++;
- } while (nbits > 0);
+ cur_bit += nbits;
+ } while (cur_bit <= last_bit);
}
EXPORT_SYMBOL_GPL(iova_bitmap_set);
--
2.35.1