On Tue, Nov 20, 2018 at 03:01:33PM +0000, Robin Murphy wrote: > On 20/11/2018 14:49, Konrad Rzeszutek Wilk wrote: > > On Tue, Nov 20, 2018 at 02:09:52PM +0000, Robin Murphy wrote: > > > With the overflow buffer removed, we no longer have a unique address > > > which is guaranteed not to be a valid DMA target to use as an error > > > token. The DIRECT_MAPPING_ERROR value of 0 tries to at least represent > > > an unlikely DMA target, but unfortunately there are already SWIOTLB > > > users with DMA-able memory at physical address 0 which now gets falsely > > > treated as a mapping failure and leads to all manner of misbehaviour. > > > > > > The best we can do to mitigate that is flip DIRECT_MAPPING_ERROR to the > > > commonly-used all-bits-set value, since the last single byte of memory > > > is by far the least-likely-valid DMA target. > > > > Are all the callers checking for DIRECT_MAPPING_ERROR or is it more of > > a comparison (as in if (!ret)) ? > > dma_direct_map_page() and dma_direct_mapping_error() were already doing the > right thing, and external callers must rely on the latter via > dma_mapping_error() rather than trying to inspect the actual value > themselves, since that varies between implementations anyway. AFAICS all the > new return paths from swiotlb_map_page() are also robust in referencing the > macro explicitly, so I think we're good.
Cool! Thank you for checking. Acked-by: Konrad Rzeszutek Wilk <[email protected]> Thank you! > > Thanks, > Robin. > > > > Fixes: dff8d6c1ed58 ("swiotlb: remove the overflow buffer")] > > > Reported-by: John Stultz <[email protected]> > > > Signed-off-by: Robin Murphy <[email protected]> > > > --- > > > include/linux/dma-direct.h | 2 +- > > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > > > diff --git a/include/linux/dma-direct.h b/include/linux/dma-direct.h > > > index bd73e7a91410..9de9c7ab39d6 100644 > > > --- a/include/linux/dma-direct.h > > > +++ b/include/linux/dma-direct.h > > > @@ -5,7 +5,7 @@ > > > #include <linux/dma-mapping.h> > > > #include <linux/mem_encrypt.h> > > > -#define DIRECT_MAPPING_ERROR 0 > > > +#define DIRECT_MAPPING_ERROR ~(dma_addr_t)0 > > > #ifdef CONFIG_ARCH_HAS_PHYS_TO_DMA > > > #include <asm/dma-direct.h> > > > -- > > > 2.19.1.dirty > > > _______________________________________________ iommu mailing list [email protected] https://lists.linuxfoundation.org/mailman/listinfo/iommu
