iommufd/selftest: Fix dirty bitmap tests with u8 bitmaps

With 64k base pages, the first 128k iova length test requires less than a
byte for a bitmap, exposing a bug in the tests that assume that bitmaps are
at least a byte.

Rather than dealing with bytes, have _test_mock_dirty_bitmaps() pass the
number of bits. The caller functions are adjusted to also use bits as well,
and converting to bytes when clearing, allocating and freeing the bitmap.

Link: https://lore.kernel.org/r/20240627110105.62325-2-joao.m.martins@oracle.comReported-by: Matt Ochs <mochs@nvidia.com>
Fixes: a9af47e3 ("iommufd/selftest: Test IOMMU_HWPT_GET_DIRTY_BITMAP")
Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Tested-by: Matt Ochs <mochs@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

tools/testing/selftests/iommu/iommufd.c

@@ -1722,6 +1722,7 @@ FIXTURE_VARIANT(iommufd_dirty_tracking)
 
 FIXTURE_SETUP(iommufd_dirty_tracking)
 {
+	unsigned long size;
 	int mmap_flags;
 	void *vrc;
 	int rc;
@@ -1749,12 +1750,11 @@ FIXTURE_SETUP(iommufd_dirty_tracking)
 	assert(vrc == self->buffer);
 
 	self->page_size = MOCK_PAGE_SIZE;
-	self->bitmap_size =
-		variant->buffer_size / self->page_size / BITS_PER_BYTE;
+	self->bitmap_size = variant->buffer_size / self->page_size;
 
 	/* Provision with an extra (PAGE_SIZE) for the unaligned case */
-	rc = posix_memalign(&self->bitmap, PAGE_SIZE,
-			    self->bitmap_size + PAGE_SIZE);
+	size = DIV_ROUND_UP(self->bitmap_size, BITS_PER_BYTE);
+	rc = posix_memalign(&self->bitmap, PAGE_SIZE, size + PAGE_SIZE);
 	assert(!rc);
 	assert(self->bitmap);
 	assert((uintptr_t)self->bitmap % PAGE_SIZE == 0);
@@ -1775,7 +1775,7 @@ FIXTURE_SETUP(iommufd_dirty_tracking)
 FIXTURE_TEARDOWN(iommufd_dirty_tracking)
 {
 	munmap(self->buffer, variant->buffer_size);
-	munmap(self->bitmap, self->bitmap_size);
+	munmap(self->bitmap, DIV_ROUND_UP(self->bitmap_size, BITS_PER_BYTE));
 	teardown_iommufd(self->fd, _metadata);
 }
 

tools/testing/selftests/iommu/iommufd_utils.h

@@ -22,6 +22,8 @@
 #define BIT_MASK(nr) (1UL << ((nr) % __BITS_PER_LONG))
 #define BIT_WORD(nr) ((nr) / __BITS_PER_LONG)
 
+#define DIV_ROUND_UP(n, d) (((n) + (d) - 1) / (d))
+
 static inline void set_bit(unsigned int nr, unsigned long *addr)
 {
 	unsigned long mask = BIT_MASK(nr);
@@ -346,12 +348,12 @@ static int _test_cmd_mock_domain_set_dirty(int fd, __u32 hwpt_id, size_t length,
 static int _test_mock_dirty_bitmaps(int fd, __u32 hwpt_id, size_t length,
 				    __u64 iova, size_t page_size,
 				    size_t pte_page_size, __u64 *bitmap,
-				    __u64 bitmap_size, __u32 flags,
+				    __u64 nbits, __u32 flags,
 				    struct __test_metadata *_metadata)
 {
 	unsigned long npte = pte_page_size / page_size, pteset = 2 * npte;
-	unsigned long nbits = bitmap_size * BITS_PER_BYTE;
 	unsigned long j, i, nr = nbits / pteset ?: 1;
+	unsigned long bitmap_size = DIV_ROUND_UP(nbits, BITS_PER_BYTE);
 	__u64 out_dirty = 0;
 
 	/* Mark all even bits as dirty in the mock domain */