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Subject[PATCH 3/3] swiotlb: ensure a segment doesn't cross the area boundary
Date
Free slots tracking assumes that slots in a segment can be allocated to
fulfill a request. This implies that slots in a segment should belong to
the same area. Although the possibility of a violation is low, it is better
to explicitly enforce segments won't span multiple areas by adjusting the
number of slabs when configuring areas.

Signed-off-by: Chao Gao <chao.gao@intel.com>
---
kernel/dma/swiotlb.c | 11 ++++++++++-
1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
index 9ab87d6d47bc..70fd73fc357a 100644
--- a/kernel/dma/swiotlb.c
+++ b/kernel/dma/swiotlb.c
@@ -91,12 +91,21 @@ struct io_tlb_area {
/*
* Round up number of slabs to the next power of 2. The last area is going
* be smaller than the rest if default_nslabs is not power of two.
+ * The number of slot in an area should be a multiple of IO_TLB_SEGSIZE,
+ * otherwise a segment may span two or more areas. It conflicts with free
+ * contiguous slots tracking: free slots are treated contiguous no matter
+ * whether they cross an area boundary.
*
* Return true if default_nslabs is rounded up.
*/
static bool round_up_default_nslabs(void)
{
- if (!default_nareas || is_power_of_2(default_nslabs))
+ if (!default_nareas)
+ return false;
+
+ if (default_nslabs < IO_TLB_SEGSIZE * default_nareas)
+ default_nslabs = IO_TLB_SEGSIZE * default_nareas;
+ else if (is_power_of_2(default_nslabs))
return false;

default_nslabs = roundup_pow_of_two(default_nslabs);
--
2.25.1
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