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SubjectRe: [PATCH 14/26] iommu/dma: Refactor iommu_dma_free
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On 22/04/2019 18:59, Christoph Hellwig wrote:
> From: Robin Murphy <robin.murphy@arm.com>
>
> The freeing logic was made particularly horrible by part of it being
> opaque to the arch wrapper, which led to a lot of convoluted repetition
> to ensure each path did everything in the right order. Now that it's
> all private, we can pick apart and consolidate the logically-distinct
> steps of freeing the IOMMU mapping, the underlying pages, and the CPU
> remap (if necessary) into something much more manageable.
>
> Signed-off-by: Robin Murphy <robin.murphy@arm.com>
> [various cosmetic changes to the code flow]

Hmm, I do still prefer my original flow with the dma_common_free_remap()
call right out of the way at the end rather than being a special case in
the middle of all the page-freeing (which is the kind of existing
complexity I was trying to eliminate). I guess you've done this to avoid
having "if (!dma_release_from_contiguous(...))..." twice like I ended up
with, which is fair enough I suppose - once we manage to solve the new
dma_{alloc,free}_contiguous() interface that may tip the balance so I
can always revisit this then.

> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
> drivers/iommu/dma-iommu.c | 75 ++++++++++++++++++---------------------
> 1 file changed, 35 insertions(+), 40 deletions(-)
>
> diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
> index 4632b9d301a1..9658c4cc3cfe 100644
> --- a/drivers/iommu/dma-iommu.c
> +++ b/drivers/iommu/dma-iommu.c
> @@ -916,6 +916,41 @@ static void iommu_dma_unmap_resource(struct device *dev, dma_addr_t handle,
> __iommu_dma_unmap(dev, handle, size);
> }
>
> +static void iommu_dma_free(struct device *dev, size_t size, void *cpu_addr,
> + dma_addr_t handle, unsigned long attrs)
> +{
> + size_t alloc_size = PAGE_ALIGN(size);
> + int count = alloc_size >> PAGE_SHIFT;
> + struct page *page = NULL;
> +
> + __iommu_dma_unmap(dev, handle, size);
> +
> + /* Non-coherent atomic allocation? Easy */
> + if (dma_free_from_pool(cpu_addr, alloc_size))
> + return;
> +
> + if (is_vmalloc_addr(cpu_addr)) {
> + /*
> + * If it the address is remapped, then it's either non-coherent

s/If it/If/

My "easy; more involved; most complex" narrative definitely doesn't
translate very well to a different order :)

Otherwise,

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

> + * or highmem CMA, or an iommu_dma_alloc_remap() construction.
> + */
> + struct page **pages = __iommu_dma_get_pages(cpu_addr);
> +
> + if (pages)
> + __iommu_dma_free_pages(pages, count);
> + else
> + page = vmalloc_to_page(cpu_addr);
> +
> + dma_common_free_remap(cpu_addr, alloc_size, VM_USERMAP);
> + } else {
> + /* Lowmem means a coherent atomic or CMA allocation */
> + page = virt_to_page(cpu_addr);
> + }
> +
> + if (page && !dma_release_from_contiguous(dev, page, count))
> + __free_pages(page, get_order(alloc_size));
> +}
> +
> static void *iommu_dma_alloc(struct device *dev, size_t size,
> dma_addr_t *handle, gfp_t gfp, unsigned long attrs)
> {
> @@ -985,46 +1020,6 @@ static void *iommu_dma_alloc(struct device *dev, size_t size,
> return addr;
> }
>
> -static void iommu_dma_free(struct device *dev, size_t size, void *cpu_addr,
> - dma_addr_t handle, unsigned long attrs)
> -{
> - size_t iosize = size;
> -
> - size = PAGE_ALIGN(size);
> - /*
> - * @cpu_addr will be one of 4 things depending on how it was allocated:
> - * - A remapped array of pages for contiguous allocations.
> - * - A remapped array of pages from iommu_dma_alloc_remap(), for all
> - * non-atomic allocations.
> - * - A non-cacheable alias from the atomic pool, for atomic
> - * allocations by non-coherent devices.
> - * - A normal lowmem address, for atomic allocations by
> - * coherent devices.
> - * Hence how dodgy the below logic looks...
> - */
> - if (dma_in_atomic_pool(cpu_addr, size)) {
> - __iommu_dma_unmap(dev, handle, iosize);
> - dma_free_from_pool(cpu_addr, size);
> - } else if (attrs & DMA_ATTR_FORCE_CONTIGUOUS) {
> - struct page *page = vmalloc_to_page(cpu_addr);
> -
> - __iommu_dma_unmap(dev, handle, iosize);
> - dma_release_from_contiguous(dev, page, size >> PAGE_SHIFT);
> - dma_common_free_remap(cpu_addr, size, VM_USERMAP);
> - } else if (is_vmalloc_addr(cpu_addr)){
> - struct page **pages = __iommu_dma_get_pages(cpu_addr);
> -
> - if (WARN_ON(!pages))
> - return;
> - __iommu_dma_unmap(dev, handle, iosize);
> - __iommu_dma_free_pages(pages, size >> PAGE_SHIFT);
> - dma_common_free_remap(cpu_addr, size, VM_USERMAP);
> - } else {
> - __iommu_dma_unmap(dev, handle, iosize);
> - __free_pages(virt_to_page(cpu_addr), get_order(size));
> - }
> -}
> -
> static int __iommu_dma_mmap_pfn(struct vm_area_struct *vma,
> unsigned long pfn, size_t size)
> {
>

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