From 03d70617b8a789c3721afaafde06fcbba7c7ebf1 Mon Sep 17 00:00:00 2001 From: Andrew Lewis Date: Thu, 26 Jun 2008 19:29:05 +1000 Subject: [PATCH] powerpc: Prevent memory corruption due to cache invalidation of unaligned DMA buffer On PowerPC processors with non-coherent cache architectures the DMA subsystem calls invalidate_dcache_range() before performing a DMA read operation. If the address and length of the DMA buffer are not aligned to a cache-line boundary this can result in memory outside of the DMA buffer being invalidated in the cache. If this memory has an uncommitted store then the data will be lost and a subsequent read of that address will result in an old value being returned from main memory. Only when the DMA buffer starts on a cache-line boundary and is an exact mutiple of the cache-line size can invalidate_dcache_range() be called, otherwise flush_dcache_range() must be called. flush_dcache_range() will first flush uncommitted writes, and then invalidate the cache. Signed-off-by: Andrew Lewis Signed-off-by: Paul Mackerras --- arch/powerpc/lib/dma-noncoherent.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-) diff --git a/arch/powerpc/lib/dma-noncoherent.c b/arch/powerpc/lib/dma-noncoherent.c index 6656d47841d0..5d83907f6591 100644 --- a/arch/powerpc/lib/dma-noncoherent.c +++ b/arch/powerpc/lib/dma-noncoherent.c @@ -348,8 +348,15 @@ void __dma_sync(void *vaddr, size_t size, int direction) switch (direction) { case DMA_NONE: BUG(); - case DMA_FROM_DEVICE: /* invalidate only */ - invalidate_dcache_range(start, end); + case DMA_FROM_DEVICE: + /* + * invalidate only when cache-line aligned otherwise there is + * the potential for discarding uncommitted data from the cache + */ + if ((start & (L1_CACHE_BYTES - 1)) || (size & (L1_CACHE_BYTES - 1))) + flush_dcache_range(start, end); + else + invalidate_dcache_range(start, end); break; case DMA_TO_DEVICE: /* writeback only */ clean_dcache_range(start, end); -- 2.20.1