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Message-ID: <6eaea467-cc50-acbd-6232-892011fc803c@cybernetics.com>
Date:   Tue, 7 Jun 2022 14:42:09 -0400
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Subject: [PATCH v6 04/11] dmapool: fix boundary comparison
Content-Language: en-US
From:   Tony Battersby <tonyb@cybernetics.com>
To:     linux-mm@kvack.org, linux-kernel@vger.kernel.org
Cc:     iommu@lists.linux-foundation.org, kernel-team@fb.com,
        Matthew Wilcox <willy@infradead.org>,
        Keith Busch <kbusch@kernel.org>,
        Andy Shevchenko <andy.shevchenko@gmail.com>,
        Robin Murphy <robin.murphy@arm.com>,
        Tony Lindgren <tony@atomide.com>
References: <340ff8ef-9ff5-7175-c234-4132bbdfc5f7@cybernetics.com>
In-Reply-To: <340ff8ef-9ff5-7175-c234-4132bbdfc5f7@cybernetics.com>
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Precedence: bulk

Fix the boundary comparison when constructing the list of free blocks
for the case that 'size' is a power of two.  Since 'boundary' is also a
power of two, that would make 'boundary' a multiple of 'size', in which
case a single block would never cross the boundary.  This bug would
cause some of the allocated memory to be wasted (but not leaked).

Example:

size       = 512
boundary   = 2048
allocation = 4096

Address range
   0 -  511
 512 - 1023
1024 - 1535
1536 - 2047 *
2048 - 2559
2560 - 3071
3072 - 3583
3584 - 4095 *

Prior to this fix, the address ranges marked with "*" would not have
been used even though they didn't cross the given boundary.

Fixes: e34f44b3517f ("pool: Improve memory usage for devices which can't cross boundaries")
Signed-off-by: Tony Battersby <tonyb@cybernetics.com>
---
 mm/dmapool.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/dmapool.c b/mm/dmapool.c
index f85d6bde2205..122781fe2c03 100644
--- a/mm/dmapool.c
+++ b/mm/dmapool.c
@@ -201,7 +201,7 @@ static void pool_initialise_page(struct dma_pool *pool, struct dma_page *page)
 
 	do {
 		unsigned int next = offset + pool->size;
-		if (unlikely((next + pool->size) >= next_boundary)) {
+		if (unlikely((next + pool->size) > next_boundary)) {
 			next = next_boundary;
 			next_boundary += pool->boundary;
 		}
-- 
2.25.1