Re: [PATCH 10/22] swiotlb: refactor coherent buffer allocation

Robin Murphy
2018-01-10T12:22:27Z

On 10/01/18 08:09, Christoph Hellwig wrote:
> Factor out a new swiotlb_alloc_buffer helper that allocates DMA coherent
> memory from the swiotlb bounce buffer.
>
> This allows to simplify the swiotlb_alloc implemenation that uses
> dma_direct_alloc to try to allocate a reachable buffer first.
>
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
> lib/swiotlb.c | 122 +++++++++++++++++++++++++++++++---------------------------
> 1 file changed, 65 insertions(+), 57 deletions(-)
>
> diff --git a/lib/swiotlb.c b/lib/swiotlb.c
> index 1a147f1354a1..bf2d19ee91c1 100644
> --- a/lib/swiotlb.c
> +++ b/lib/swiotlb.c
> @@ -709,75 +709,79 @@ void swiotlb_tbl_sync_single(struct device *hwdev, phys_addr_t tlb_addr,
> }
> EXPORT_SYMBOL_GPL(swiotlb_tbl_sync_single);
>
> -void *
> -swiotlb_alloc_coherent(struct device *hwdev, size_t size,
> - dma_addr_t *dma_handle, gfp_t flags)
> +static inline bool dma_coherent_ok(struct device *dev, dma_addr_t addr,
> + size_t size)
> {
> - bool warn = !(flags & __GFP_NOWARN);
> - dma_addr_t dev_addr;
> - void *ret;
> - int order = get_order(size);
> - u64 dma_mask = DMA_BIT_MASK(32);
> + u64 mask = DMA_BIT_MASK(32);
>
> - if (hwdev && hwdev->coherent_dma_mask)
> - dma_mask = hwdev->coherent_dma_mask;
> + if (dev && dev->coherent_dma_mask)
> + mask = dev->coherent_dma_mask;
> + return addr + size - 1 <= mask;
> +}
>
> - ret = (void *)__get_free_pages(flags, order);
> - if (ret) {
> - dev_addr = swiotlb_virt_to_bus(hwdev, ret);
> - if (dev_addr + size - 1 > dma_mask) {
> - /*
> - * The allocated memory isn't reachable by the device.
> - */
> - free_pages((unsigned long) ret, order);
> - ret = NULL;
> - }
> - }
> - if (!ret) {
> - /*
> - * We are either out of memory or the device can't DMA to
> - * GFP_DMA memory; fall back on map_single(), which
> - * will grab memory from the lowest available address range.
> - */
> - phys_addr_t paddr = map_single(hwdev, 0, size, DMA_FROM_DEVICE,
> - warn ? 0 : DMA_ATTR_NO_WARN);
> - if (paddr == SWIOTLB_MAP_ERROR)
> - goto err_warn;
> +static void *
> +swiotlb_alloc_buffer(struct device *dev, size_t size, dma_addr_t *dma_handle,
> + unsigned long attrs)
> +{
> + phys_addr_t phys_addr;
> +
> + if (swiotlb_force == SWIOTLB_NO_FORCE)
> + goto out_warn;
>
> - ret = phys_to_virt(paddr);
> - dev_addr = swiotlb_phys_to_dma(hwdev, paddr);
> + phys_addr = swiotlb_tbl_map_single(dev,
> + swiotlb_phys_to_dma(dev, io_tlb_start),
> + 0, size, DMA_FROM_DEVICE, 0);
> + if (phys_addr == SWIOTLB_MAP_ERROR)
> + goto out_warn;
>
> - /* Confirm address can be DMA'd by device */
> - if (dev_addr + size - 1 > dma_mask) {
> - printk("hwdev DMA mask = 0x%016Lx, dev_addr = 0x%016Lx\n",
> - (unsigned long long)dma_mask,
> - (unsigned long long)dev_addr);
> + *dma_handle = swiotlb_phys_to_dma(dev, phys_addr);

nit: this should probably go after the dma_coherent_ok() check (as with
the original logic).

>
> - /*
> - * DMA_TO_DEVICE to avoid memcpy in unmap_single.
> - * The DMA_ATTR_SKIP_CPU_SYNC is optional.
> - */
> - swiotlb_tbl_unmap_single(hwdev, paddr,
> - size, DMA_TO_DEVICE,
> - DMA_ATTR_SKIP_CPU_SYNC);
> - goto err_warn;
> - }
> - }
> + if (dma_coherent_ok(dev, *dma_handle, size))
> + goto out_unmap;
>
> - *dma_handle = dev_addr;
> - memset(ret, 0, size);
> + memset(phys_to_virt(phys_addr), 0, size);
> + return phys_to_virt(phys_addr);
>
> - return ret;
> +out_unmap:
> + dev_warn(dev, "hwdev DMA mask = 0x%016Lx, dev_addr = 0x%016Lx\n",
> + (unsigned long long)(dev ? dev->coherent_dma_mask : 0),
> + (unsigned long long)*dma_handle);
>
> -err_warn:
> - if (warn && printk_ratelimit()) {
> - pr_warn("swiotlb: coherent allocation failed for device %s size=%zu\n",
> - dev_name(hwdev), size);
> + /*
> + * DMA_TO_DEVICE to avoid memcpy in unmap_single.
> + * DMA_ATTR_SKIP_CPU_SYNC is optional.
> + */
> + swiotlb_tbl_unmap_single(dev, phys_addr, size, DMA_TO_DEVICE,
> + DMA_ATTR_SKIP_CPU_SYNC);
> +out_warn:
> + if ((attrs & DMA_ATTR_NO_WARN) && printk_ratelimit()) {
> + dev_warn(dev,
> + "swiotlb: coherent allocation failed, size=%zu\n",
> + size);
> dump_stack();
> }
> -
> return NULL;
> }
> +
> +void *
> +swiotlb_alloc_coherent(struct device *hwdev, size_t size,
> + dma_addr_t *dma_handle, gfp_t flags)
> +{
> + int order = get_order(size);
> + unsigned long attrs = (flags & __GFP_NOWARN) ? DMA_ATTR_NO_WARN : 0;
> + void *ret;
> +
> + ret = (void *)__get_free_pages(flags, order);
> + if (ret) {
> + *dma_handle = swiotlb_virt_to_bus(hwdev, ret);
> + if (dma_coherent_ok(hwdev, *dma_handle, size)) {
> + memset(ret, 0, size);
> + return ret;
> + }

Aren't we leaking the pages here?

Robin.

> + }
> +
> + return swiotlb_alloc_buffer(hwdev, size, dma_handle, attrs);
> +}
> EXPORT_SYMBOL(swiotlb_alloc_coherent);
>
> static bool swiotlb_free_buffer(struct device *dev, size_t size,
> @@ -1103,6 +1107,10 @@ void *swiotlb_alloc(struct device *dev, size_t size, dma_addr_t *dma_handle,
> {
> void *vaddr;
>
> + /* temporary workaround: */
> + if (gfp & __GFP_NOWARN)
> + attrs |= DMA_ATTR_NO_WARN;
> +
> /*
> * Don't print a warning when the first allocation attempt fails.
> * swiotlb_alloc_coherent() will print a warning when the DMA memory
> @@ -1112,7 +1120,7 @@ void *swiotlb_alloc(struct device *dev, size_t size, dma_addr_t *dma_handle,
>
> vaddr = dma_direct_alloc(dev, size, dma_handle, gfp, attrs);
> if (!vaddr)
> - vaddr = swiotlb_alloc_coherent(dev, size, dma_handle, gfp);
> + vaddr = swiotlb_alloc_buffer(dev, size, dma_handle, attrs);
> return vaddr;
> }
>
>