On 2021-04-01 09:47, Will Deacon wrote:
Avoid the potential for shifting values by amounts greater than the
width of their type by using a bitmap to compute page size in
iommu_pgsize().
Signed-off-by: Will Deacon <w...@kernel.org>
---
drivers/iommu/iommu.c | 31 ++++++++++++-------------------
1 file changed, 12 insertions(+), 19 deletions(-)
diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index d0b0a15dba84..bcd623862bf9 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -8,6 +8,7 @@
#include <linux/device.h>
#include <linux/kernel.h>
+#include <linux/bits.h>
#include <linux/bug.h>
#include <linux/types.h>
#include <linux/init.h>
@@ -2360,30 +2361,22 @@ static size_t iommu_pgsize(struct iommu_domain
*domain,
unsigned long addr_merge, size_t size)
{
unsigned int pgsize_idx;
+ unsigned long pgsizes;
size_t pgsize;
- /* Max page size that still fits into 'size' */
- pgsize_idx = __fls(size);
+ /* Page sizes supported by the hardware and small enough for @size */
+ pgsizes = domain->pgsize_bitmap & GENMASK(__fls(size), 0);
I've fixed this in the latest RFC for the iommu_map/unmap optimization
patches,
but for the sake of completeness: I think this should be GENMASK_ULL, in
case
__fls(size) >= 32.
Thank you for these patches, by the way. I've looked through them and
they
make sense/seem correct. I've integrated them into the latest RFC:
https://lore.kernel.org/linux-iommu/20210402013452.4013-1-isa...@codeaurora.org/T/#t.
Thanks,
Isaac
- /* need to consider alignment requirements ? */
- if (likely(addr_merge)) {
- /* Max page size allowed by address */
- unsigned int align_pgsize_idx = __ffs(addr_merge);
- pgsize_idx = min(pgsize_idx, align_pgsize_idx);
- }
-
- /* build a mask of acceptable page sizes */
- pgsize = (1UL << (pgsize_idx + 1)) - 1;
-
- /* throw away page sizes not supported by the hardware */
- pgsize &= domain->pgsize_bitmap;
+ /* Constrain the page sizes further based on the maximum alignment */
+ if (likely(addr_merge))
+ pgsizes &= GENMASK(__ffs(addr_merge), 0);
- /* make sure we're still sane */
- BUG_ON(!pgsize);
+ /* Make sure we have at least one suitable page size */
+ BUG_ON(!pgsizes);
- /* pick the biggest page */
- pgsize_idx = __fls(pgsize);
- pgsize = 1UL << pgsize_idx;
+ /* Pick the biggest page size remaining */
+ pgsize_idx = __fls(pgsizes);
+ pgsize = BIT(pgsize_idx);
return pgsize;
}
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