[PATCH v6 2/3] arm64: Add IOMMU dma_ops

[Yong Wu]

On Thu, 2015-10-01 at 20:13 +0100, Robin Murphy wrote:
> Taking some inspiration from the arch/arm code, implement the
> arch-specific side of the DMA mapping ops using the new IOMMU-DMA layer.
[...]
> +static void *__iommu_alloc_attrs(struct device *dev, size_t size,
> +				 dma_addr_t *handle, gfp_t gfp,
> +				 struct dma_attrs *attrs)
> +{
> +	bool coherent = is_device_dma_coherent(dev);
> +	int ioprot = dma_direction_to_prot(DMA_BIDIRECTIONAL, coherent);
> +	void *addr;
> +
> +	if (WARN(!dev, "cannot create IOMMU mapping for unknown device\n"))
> +		return NULL;
> +	/*
> +	 * Some drivers rely on this, and we probably don't want the
> +	 * possibility of stale kernel data being read by devices anyway.
> +	 */
> +	gfp |= __GFP_ZERO;
> +
> +	if (gfp & __GFP_WAIT) {
> +		struct page **pages;
> +		pgprot_t prot = __get_dma_pgprot(attrs, PAGE_KERNEL, coherent);
> +
> +		pages = iommu_dma_alloc(dev, size, gfp, ioprot,	handle,
> +					flush_page);
> +		if (!pages)
> +			return NULL;
> +
> +		addr = dma_common_pages_remap(pages, size, VM_USERMAP, prot,
> +					      __builtin_return_address(0));
> +		if (!addr)
> +			iommu_dma_free(dev, pages, size, handle);
> +	} else {
> +		struct page *page;
> +		/*
> +		 * In atomic context we can't remap anything, so we'll only
> +		 * get the virtually contiguous buffer we need by way of a
> +		 * physically contiguous allocation.
> +		 */
> +		if (coherent) {
> +			page = alloc_pages(gfp, get_order(size));
> +			addr = page ? page_address(page) : NULL;
> +		} else {
> +			addr = __alloc_from_pool(size, &page, gfp);
> +		}
> +		if (!addr)
> +			return NULL;
> +
> +		*handle = iommu_dma_map_page(dev, page, 0, size, ioprot);
> +		if (iommu_dma_mapping_error(dev, *handle)) {
> +			if (coherent)
> +				__free_pages(page, get_order(size));
> +			else
> +				__free_from_pool(addr, size);
> +			addr = NULL;
> +		}
> +	}
> +	return addr;
> +}
> +
> +static void __iommu_free_attrs(struct device *dev, size_t size, void *cpu_addr,
> +			       dma_addr_t handle, struct dma_attrs *attrs)
> +{
> +	/*
> +	 * @cpu_addr will be one of 3 things depending on how it was allocated:
> +	 * - A remapped array of pages from iommu_dma_alloc(), 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 (__in_atomic_pool(cpu_addr, size)) {
> +		iommu_dma_unmap_page(dev, handle, size, 0, NULL);
> +		__free_from_pool(cpu_addr, size);
> +	} else if (is_vmalloc_addr(cpu_addr)){
> +		struct vm_struct *area = find_vm_area(cpu_addr);
> +
> +		if (WARN_ON(!area || !area->pages))
> +			return;
> +		iommu_dma_free(dev, area->pages, size, &handle);
> +		dma_common_free_remap(cpu_addr, size, VM_USERMAP);

Hi Robin,
    We get a WARN issue while the size is not aligned here.

    The WARN log is:
[  206.852002] WARNING: CPU: 0 PID: 23329
at /mnt/host/source/src/third_party/kernel/v3.18/mm/vmalloc.c:65
vunmap_page_range+0x190/0x1b4()
[  206.864438] Modules linked in: nls_iso8859_1 nls_cp437 vfat fat
rfcomm i2c_dev uinput dm9601 uvcvideo btmrvl_sdio mwifiex_sdio mwifiex
btmrvl bluetooth zram fuse cfg80211 nf_conntrack_ipv6 nf_defrag_ipv6
ip6table_filter ip6_tables cdc_ether usbnet mii joydev snd_seq_midi
snd_seq_midi_event snd_rawmidi snd_seq snd_seq_device ppp_async
ppp_generic slhc tun
[  206.902983] CPU: 0 PID: 23329 Comm: chrome Not tainted 3.18.0 #17
[  206.910430] Hardware name: Mediatek Oak rev3 board (DT)
[  206.920018] Call trace:
[  206.925537] [<ffffffc000208c00>] dump_backtrace+0x0/0x140
[  206.931905] [<ffffffc000208d5c>] show_stack+0x1c/0x28
[  206.939158] [<ffffffc000870f80>] dump_stack+0x74/0x94
[  206.947459] [<ffffffc0002219a4>] warn_slowpath_common+0x90/0xb8
[  206.954100] [<ffffffc000221b58>] warn_slowpath_null+0x34/0x44
[  206.961537] [<ffffffc000321358>] vunmap_page_range+0x18c/0x1b4
[  206.967630] [<ffffffc0003213e4>] unmap_kernel_range+0x2c/0x78
[  206.976977] [<ffffffc000582224>] dma_common_free_remap+0x68/0x80
[  206.983581] [<ffffffc000217260>] __iommu_free_attrs+0x14c/0x160
[  206.989646] [<ffffffc00066fc1c>] mtk_vcodec_mem_free+0xa0/0x15c
[  206.996481] [<ffffffc00067e278>] vp9_free_work_buf+0x54/0x70
[  207.002260] [<ffffffc00067f168>] vdec_vp9_deinit+0x7c/0xe8
[  207.008134] [<ffffffc0006787d8>] vdec_if_deinit+0x84/0xec
[  207.013820] [<ffffffc000677898>] mtk_vcodec_vdec_release+0x54/0x6c
[  207.020672] [<ffffffc000673e3c>] fops_vcodec_release+0x7c/0xf8
[  207.026607] [<ffffffc000652b78>] v4l2_release+0x3c/0x84
[  207.031824] [<ffffffc00033b218>] __fput+0xf8/0x1c0
[  207.036599] [<ffffffc00033b350>] ____fput+0x1c/0x2c
[  207.041454] [<ffffffc00023ed78>] task_work_run+0xb0/0xd4
[  207.046756] [<ffffffc00020872c>] do_notify_resume+0x54/0x6c


   From the log I get in this fail case, the size of unmap here is
0x10080, and its map size of dma_common_pages_remap in
__iommu_alloc_attrs is 0x10080, and the corresponding dma-map size is
0x11000(after iova_align). I think all the parameters of map and unmap
are good, it look like not a DMA issue. but I don't know why we get this
warning.
Have you met this problem and give us some advices, Thanks.

(If we add PAGE_ALIGN for the size in dma_alloc and dma_free, It is OK.)

> +	} else {
> +		iommu_dma_unmap_page(dev, handle, size, 0, NULL);
> +		__free_pages(virt_to_page(cpu_addr), get_order(size));
> +	}
> +}
> +
[...]