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SubjectRe: [PATCH 3/5] dma-direct: refine dma_direct_alloc zone selection
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On 20/09/18 19:52, Christoph Hellwig wrote:
> We need to take the DMA offset and encryption bit into account when
> selecting a zone. User the opportunity to factor out the zone
> selection into a helper for reuse.
>
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
> kernel/dma/direct.c | 31 +++++++++++++++++++++----------
> 1 file changed, 21 insertions(+), 10 deletions(-)
>
> diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
> index 81b73a5bba54..3c404e33d946 100644
> --- a/kernel/dma/direct.c
> +++ b/kernel/dma/direct.c
> @@ -68,6 +68,22 @@ u64 dma_direct_get_required_mask(struct device *dev)
> return (1ULL << (fls64(max_dma) - 1)) * 2 - 1;
> }
>
> +static gfp_t __dma_direct_optimal_gfp_mask(struct device *dev, u64 dma_mask,
> + u64 *phys_mask)
> +{
> + if (force_dma_unencrypted())
> + *phys_mask = __dma_to_phys(dev, dma_mask);
> + else
> + *phys_mask = dma_to_phys(dev, dma_mask);

Maybe make phys_to_dma_direct() take u64 instead of phys_addr_t so we
can reuse it here?

> + /* GFP_DMA32 and GFP_DMA are no ops without the corresponding zones: */
> + if (*phys_mask <= DMA_BIT_MASK(ARCH_ZONE_DMA_BITS))
> + return GFP_DMA;

If we don't have ZONE_DMA it would in theory be a tiny bit better to
fall back to GFP_DMA32 instead of returning 0 here, but I'm not sure
it's worth the bother.

> + if (*phys_mask <= DMA_BIT_MASK(32))
> + return GFP_DMA32;
> + return 0;
> +}
> +
> static bool dma_coherent_ok(struct device *dev, phys_addr_t phys, size_t size)
> {
> return phys_to_dma_direct(dev, phys) + size - 1 <=
> @@ -80,17 +96,13 @@ void *dma_direct_alloc_pages(struct device *dev, size_t size,
> unsigned int count = PAGE_ALIGN(size) >> PAGE_SHIFT;
> int page_order = get_order(size);
> struct page *page = NULL;
> + u64 phys_mask;
> void *ret;
>
> /* we always manually zero the memory once we are done: */
> gfp &= ~__GFP_ZERO;
> -
> - /* GFP_DMA32 and GFP_DMA are no ops without the corresponding zones: */
> - if (dev->coherent_dma_mask <= DMA_BIT_MASK(ARCH_ZONE_DMA_BITS))
> - gfp |= GFP_DMA;
> - if (dev->coherent_dma_mask <= DMA_BIT_MASK(32) && !(gfp & GFP_DMA))
> - gfp |= GFP_DMA32;
> -
> + gfp |= __dma_direct_optimal_gfp_mask(dev, dev->coherent_dma_mask,
> + &phys_mask);
> again:
> /* CMA can be used only in the context which permits sleeping */
> if (gfpflags_allow_blocking(gfp)) {
> @@ -109,15 +121,14 @@ void *dma_direct_alloc_pages(struct device *dev, size_t size,
> page = NULL;
>
> if (IS_ENABLED(CONFIG_ZONE_DMA32) &&
> - dev->coherent_dma_mask < DMA_BIT_MASK(64) &&
> + phys_mask < DMA_BIT_MASK(64) &&
> !(gfp & (GFP_DMA32 | GFP_DMA))) {
> gfp |= GFP_DMA32;
> goto again;

Ah right, in that situation we should probably end up here anyway, so
that's good enough - definitely not worth any more #ifdeffery above.
Nits aside,

Reviewed-by: Robin Murphy <robin.murphy@arm.com>

> }
>
> if (IS_ENABLED(CONFIG_ZONE_DMA) &&
> - dev->coherent_dma_mask < DMA_BIT_MASK(32) &&
> - !(gfp & GFP_DMA)) {
> + phys_mask < DMA_BIT_MASK(32) && !(gfp & GFP_DMA)) {
> gfp = (gfp & ~GFP_DMA32) | GFP_DMA;
> goto again;
> }
>

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