swiotlb: fix a braino in the alignment check fix

The alignment mask in swiotlb_do_find_slots() masks off the high
bits which are not relevant for the alignment, so multiple
requirements are combined with a bitwise OR rather than AND.
In plain English, the stricter the alignment, the more bits must
be set in iotlb_align_mask.

Confusion may arise from the fact that the same variable is also
used to mask off the offset within a swiotlb slot, which is
achieved with a bitwise AND.

Fixes: 0eee5ae10256 ("swiotlb: fix slot alignment checks")
Reported-by: Dexuan Cui <decui@microsoft.com>
Link: https://lore.kernel.org/all/CAA42JLa1y9jJ7BgQvXeUYQh-K2mDNHd2BYZ4iZUz33r5zY7oAQ@mail.gmail.com/
Reported-by: Kelsey Steele <kelseysteele@linux.microsoft.com>
Link: https://lore.kernel.org/all/20230405003549.GA21326@linuxonhyperv3.guj3yctzbm1etfxqx2vob5hsef.xx.internal.cloudapp.net/
Signed-off-by: Petr Tesarik <petr.tesarik.ext@huawei.com>
Tested-by: Dexuan Cui <decui@microsoft.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>

diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
index 5b919ef832b6f628d844183ab0d04cb96bba9cea..dac42a2ad5883c16b851dc94c53d17c638a91b66 100644 (file)
--- a/kernel/dma/swiotlb.c
+++ b/kernel/dma/swiotlb.c
@@ -623,7 +623,7 @@ static int swiotlb_do_find_slots(struct device *dev, int area_index,
                phys_to_dma_unencrypted(dev, mem->start) & boundary_mask;
        unsigned long max_slots = get_max_slots(boundary_mask);
        unsigned int iotlb_align_mask =
-               dma_get_min_align_mask(dev) & ~(IO_TLB_SIZE - 1);
+               dma_get_min_align_mask(dev) | alloc_align_mask;
        unsigned int nslots = nr_slots(alloc_size), stride;
        unsigned int offset = swiotlb_align_offset(dev, orig_addr);
        unsigned int index, slots_checked, count = 0, i;
@@ -639,8 +639,8 @@ static int swiotlb_do_find_slots(struct device *dev, int area_index,
         * allocations.
         */
        if (alloc_size >= PAGE_SIZE)
-               iotlb_align_mask &= PAGE_MASK;
-       iotlb_align_mask &= alloc_align_mask;
+               iotlb_align_mask |= ~PAGE_MASK;
+       iotlb_align_mask &= ~(IO_TLB_SIZE - 1);
 
        /*
         * For mappings with an alignment requirement don't bother looping to