Messages in this thread | | | From | Tomasz Figa <> | Date | Tue, 27 Jun 2017 20:17:55 +0900 | Subject | Re: [PATCH 1/2] iommu/dma: Respect __GFP_DMA and __GFP_DMA32 in incoming GFP flags |
| |
On Tue, Jun 27, 2017 at 8:01 PM, Robin Murphy <robin.murphy@arm.com> wrote: > On 27/06/17 08:28, Tomasz Figa wrote: >> Current implementation of __iommu_dma_alloc_pages() keeps adding >> __GFP_HIGHMEM to GFP flags regardless of whether other zone flags are >> already included in the incoming flags. If __GFP_DMA or __GFP_DMA32 is >> set at the same time as __GFP_HIGHMEM, the allocation fails due to >> invalid zone flag combination. >> >> Fix this by checking for __GFP_DMA and __GFP_DMA32 in incoming GFP flags >> and adding __GFP_HIGHMEM only if they are not present. > > Wouldn't it make more sense to strip off the ZONE_DMA* related flags, > since the whole point here is that we don't care where the pages come from?
I guess for my use case it wouldn't break things, as I strip them in my DMA mapping implementation right now (+/- one minor detail below).
However I recall existing IOMMUs that could only use pages from within the 32-bit address space (e.g. Tegra X1). Also the IOMMU I'm working on is a part of a PCI device and it might actually prefer 32-bit addressable memory as well (to avoid DAC addressing; I still need to evaluate this). With this said, maybe it could actually make sense to leave the choice to the DMA mapping implementation?
Best regards, Tomasz
> > Robin. > >> Signed-off-by: Tomasz Figa <tfiga@chromium.org> >> --- >> drivers/iommu/dma-iommu.c | 10 ++++++++-- >> 1 file changed, 8 insertions(+), 2 deletions(-) >> >> diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c >> index 9d1cebe7f6cb..29965a092a69 100644 >> --- a/drivers/iommu/dma-iommu.c >> +++ b/drivers/iommu/dma-iommu.c >> @@ -445,8 +445,14 @@ static struct page **__iommu_dma_alloc_pages(unsigned int count, >> if (!pages) >> return NULL; >> >> - /* IOMMU can map any pages, so himem can also be used here */ >> - gfp |= __GFP_NOWARN | __GFP_HIGHMEM; >> + /* >> + * IOMMU can map any pages, so himem can also be used here, >> + * unless another DMA zone is explicitly requested. >> + */ >> + if (!(gfp & (__GFP_DMA | __GFP_DMA32))) >> + gfp |= __GFP_HIGHMEM; >> + >> + gfp |= __GFP_NOWARN; >> >> while (count) { >> struct page *page = NULL; >> >
| |