On 7/22/2014 2:03 PM, Catalin Marinas wrote: > On Tue, Jul 22, 2014 at 07:06:44PM +0100, Arnd Bergmann wrote: [...] >>> + if (!addr) >>> + goto destroy_genpool; >>> + >>> + memset(addr, 0, atomic_pool_size); >>> + __dma_flush_range(addr, addr + atomic_pool_size); >> >> It also seems weird to flush the cache on a virtual address of >> an uncacheable mapping. Is that well-defined? > > Yes. According to D5.8.1 (Data and unified caches), "if cache > maintenance is performed on a memory location, the effect of that cache > maintenance is visible to all aliases of that physical memory location. > These properties are consistent with implementing all caches that can > handle data accesses as Physically-indexed, physically-tagged (PIPT) > caches". > This was actually unintentional on my part. I'm going to clean this up to flush via the existing cached mapping to make it clearer what's going on. >> In the CMA case, the >> original mapping should already be uncached here, so you don't need >> to flush it. > > I don't think it is non-cacheable already, at least not for arm64 (CMA > can be used on coherent architectures as well). > Memory allocated via dma_alloc_from_contiguous is not guaranteed to be uncached. On arm, we allocate the page of memory and the remap it as appropriate. >> In the alloc_pages() case, I think you need to unmap >> the pages from the linear mapping instead. > > Even if unmapped, it would not remove dirty cache lines (which are > associated with physical addresses anyway). But we don't need to worry > about unmapping anyway, see above (that's unless we find some > architecture implementation where having such cacheable/non-cacheable > aliases is not efficient enough, the efficiency is not guaranteed by the > ARM ARM, just the correct behaviour). > Let's hope that never happens. Thanks, Laura -- Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by The Linux Foundation -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>