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. > > >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 <[email protected]> > >Cc: Konrad Rzeszutek Wilk <[email protected]> > >Cc: David Woodhouse <[email protected]> > >Cc: Don Dutile <[email protected]> > >Cc: Thomas Gleixner <[email protected]> > >Cc: Ingo Molnar <[email protected]> > >Cc: "H. Peter Anvin" <[email protected]> > >Cc: Andi Kleen <[email protected]> > >Cc: [email protected] > >Cc: [email protected] > >Signed-off-by: Akinobu Mita <[email protected]> > >--- > >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 > _______________________________________________ iommu mailing list [email protected] https://lists.linuxfoundation.org/mailman/listinfo/iommu
