Messages in this thread | | | Date | Wed, 29 Jan 2014 08:20:45 +0900 | Subject | Re: [PATCH v2 1/5] x86: make dma_alloc_coherent() return zeroed memory if CMA is enabled | From | Akinobu Mita <> |
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2014-01-28 Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>: > On Mon, Jan 27, 2014 at 02:54:47PM +0100, Marek Szyprowski wrote: >> Hello, >> >> On 2014-01-14 15:13, Akinobu Mita wrote: >> >Calling dma_alloc_coherent() with __GFP_ZERO must return zeroed memory. >> > >> >But when the contiguous memory allocator (CMA) is enabled on x86 and >> >the memory region is allocated by dma_alloc_from_contiguous(), it >> >doesn't return zeroed memory. Because dma_generic_alloc_coherent() >> >forgot to fill the memory region with zero if it was allocated by >> >dma_alloc_from_contiguous() >> >> I just wonder how it will work with high mem? I've didn't check the x86 >> dma mapping code yet, but page_address() works only for pages, which comes >> from low memory. In other patches you have added an option to place CMA >> area anywhere in the memory. Is the x86 pci dma code ready for the case >> when cma area is put into high mem and direct mappings are not available? > > Yes and no. The swiotbl_bounce does have the code to take that into account. > But that is it - nothing else does - so I think you would run in the > possiblity of 'page_address' not providing an correct virtual address.
Thanks for spotting the issue. I haven't much tested on x86_32. I'll go through it and try to find the solution.
>> >> >Most implementations of dma_alloc_coherent() return zeroed memory >> >regardless of whether __GFP_ZERO is specified. So this fixes it by >> >unconditionally zeroing the allocated memory region. >> > >> >Cc: Marek Szyprowski <m.szyprowski@samsung.com> >> >Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> >> >Cc: David Woodhouse <dwmw2@infradead.org> >> >Cc: Don Dutile <ddutile@redhat.com> >> >Cc: Thomas Gleixner <tglx@linutronix.de> >> >Cc: Ingo Molnar <mingo@redhat.com> >> >Cc: "H. Peter Anvin" <hpa@zytor.com> >> >Cc: Andi Kleen <andi@firstfloor.org> >> >Cc: x86@kernel.org >> >Cc: iommu@lists.linux-foundation.org >> >Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com> >> >--- >> >New patch from this version >> > >> > arch/x86/kernel/pci-dma.c | 3 +-- >> > 1 file changed, 1 insertion(+), 2 deletions(-) >> > >> >diff --git a/arch/x86/kernel/pci-dma.c b/arch/x86/kernel/pci-dma.c >> >index 872079a..9644405 100644 >> >--- a/arch/x86/kernel/pci-dma.c >> >+++ b/arch/x86/kernel/pci-dma.c >> >@@ -97,7 +97,6 @@ void *dma_generic_alloc_coherent(struct device *dev, size_t size, >> > dma_mask = dma_alloc_coherent_mask(dev, flag); >> >- flag |= __GFP_ZERO; >> > again: >> > page = NULL; >> > if (!(flag & GFP_ATOMIC)) >> >@@ -118,7 +117,7 @@ again: >> > return NULL; >> > } >> >- >> >+ memset(page_address(page), 0, size); >> > *dma_addr = addr; >> > return page_address(page); >> > } >> >> Best regards >> -- >> Marek Szyprowski, PhD >> Samsung R&D Institute Poland >>
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