Messages in this thread Patch in this message | | | Date | Tue, 20 Nov 2018 09:49:18 -0500 | From | Konrad Rzeszutek Wilk <> | Subject | Re: [PATCH 1/2] swiotlb: Make DIRECT_MAPPING_ERROR viable |
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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)) ?
> > Fixes: dff8d6c1ed58 ("swiotlb: remove the overflow buffer")] > Reported-by: John Stultz <john.stultz@linaro.org> > Signed-off-by: Robin Murphy <robin.murphy@arm.com> > --- > 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 >
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