On Mon, Mar 28, 2016 at 02:32:11PM +0800, Yong Wu wrote: > Currently __iommu_dma_alloc_pages assumes that all the IOMMU support > the granule of PAGE_SIZE. It call alloc_page to try allocating memory > in the last time. Fortunately the mininum pagesize in all the > current IOMMU is SZ_4K, so this works well. > > But there may be a case in which the mininum granule of IOMMU may be > larger than PAGE_SIZE, then it will abort as the IOMMU cann't map the > discontinuous memory within a granule. For example, the pgsize_bitmap > of the IOMMU only has SZ_16K while the PAGE_SIZE is SZ_4K, then we > have to prepare SZ_16K continuous memory at least for each a granule > iommu mapping.
Did you find a driver/platform that actually needs this? I certainly think it's possible, but we don't necessarily need to fix it if it's not broken yet! Just adding a comment would be enough. Either way, a couple of review comments inline. > > Signed-off-by: Yong Wu <[email protected]> > > --- > v2: > -rebase on v4.6-rc1. > -add a new patch([1/2] add pgsize_bitmap) here. > > drivers/iommu/dma-iommu.c | 22 +++++++++++++--------- > 1 file changed, 13 insertions(+), 9 deletions(-) > > diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c > index 72d6182..75ce71e 100644 > --- a/drivers/iommu/dma-iommu.c > +++ b/drivers/iommu/dma-iommu.c > @@ -190,11 +190,13 @@ static void __iommu_dma_free_pages(struct page **pages, > int count) > kvfree(pages); > } > > -static struct page **__iommu_dma_alloc_pages(unsigned int count, gfp_t gfp) > +static struct page **__iommu_dma_alloc_pages(unsigned int count, gfp_t gfp, > + unsigned long pgsize_bitmap) > { > struct page **pages; > unsigned int i = 0, array_size = count * sizeof(*pages); > - unsigned int order = MAX_ORDER; > + int min_order = get_order(1 << __ffs(pgsize_bitmap)); 1UL > + int order = MAX_ORDER; > > if (array_size <= PAGE_SIZE) > pages = kzalloc(array_size, GFP_KERNEL); > @@ -213,13 +215,16 @@ static struct page **__iommu_dma_alloc_pages(unsigned > int count, gfp_t gfp) > /* > * Higher-order allocations are a convenience rather > * than a necessity, hence using __GFP_NORETRY until > - * falling back to single-page allocations. > + * falling back to min size allocations. > */ > - for (order = min_t(unsigned int, order, __fls(count)); > - order > 0; order--) { > - page = alloc_pages(gfp | __GFP_NORETRY, order); > + for (order = min_t(int, order, __fls(count)); > + order >= min_order; order--) { > + page = alloc_pages((order == min_order) ? gfp : > + gfp | __GFP_NORETRY, order); > if (!page) > continue; > + if (!order) > + break; Isn't this handled by the loop condition? Will
