Messages in this thread | | | Date | Fri, 7 Aug 2009 10:44:04 +0100 | From | Russell King <> | Subject | Re: [UBI UBIFS] replace vmalloc with kmalloc |
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On Fri, Aug 07, 2009 at 12:20:03PM +0300, Adrian Hunter wrote: > vmalloc allows large (> 128KiB) buffers, but kmalloc doesn't. > So we presently have no choice but to use vmalloc. > > I do not know what hardware you have or exactly what driver you > are using, but we have UBIFS on OneNAND using DMA. > See drivers/mtd/onenand/omap2.c
Hmm. Looking at that code, it's unsafe:
if (buf >= high_memory) { struct page *p1;
if (((size_t)buf & PAGE_MASK) != ((size_t)(buf + count - 1) & PAGE_MASK)) goto out_copy; p1 = vmalloc_to_page(buf); if (!p1) goto out_copy; buf = page_address(p1) + ((size_t)buf & ~PAGE_MASK); } ... dma_dst = dma_map_single(&c->pdev->dev, buf, count, DMA_FROM_DEVICE);
If you consider a VIVT cache, and with vmalloc'd pages you're passing a *different* virtual address to the DMA functions, it's not going to touch the cachelines associated with the vmalloc mapping.
The above *may* work for VIPT caches provided both the vmalloc and kernel direct mappings are of the same colour. If not, this really isn't going to be reliable for the same reason.
Basically, what's going in there is *totally* unsafe. I hope you don't place important data on this NAND device.
-- Russell King Linux kernel 2.6 ARM Linux - http://www.arm.linux.org.uk/ maintainer of:
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