linux-kernel - [PATCH 2/4] usb: usbfs: Use consistent mmap functions

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Date:   Wed, 10 May 2023 16:55:25 +0800
From:   Ruihan Li <lrh2000@....edu.cn>
To:     linux-mm@...ck.org
Cc:     linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        Pasha Tatashin <pasha.tatashin@...een.com>,
        David Hildenbrand <david@...hat.com>,
        Matthew Wilcox <willy@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Christoph Hellwig <hch@...radead.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Ruihan Li <lrh2000@....edu.cn>, stable@...r.kernel.org
Subject: [PATCH 2/4] usb: usbfs: Use consistent mmap functions

When hcd->localmem_pool is non-null, it is used to allocate DMA memory.
In this case, the dma address will be properly returned (in dma_handle),
and dma_mmap_coherent should be used to map this memory into the user
space. However, the current implementation uses pfn_remap_range, which
is supposed to map normal pages (instead of DMA pages).

Instead of repeating the logic in the memory allocation function, this
patch introduces a more robust solution. To address the previous issue,
this patch checks the type of allocated memory by testing whether
dma_handle is properly set. If dma_handle is properly returned, it means
some DMA pages are allocated and dma_mmap_coherent should be used to map
them. Otherwise, normal pages are allocated and pfn_remap_range should
be called. This ensures that the correct mmap functions are used
consistently, independently with logic details that determine which type
of memory gets allocated.

Fixes: a0e710a7def4 ("USB: usbfs: fix mmap dma mismatch")
Cc: stable@...r.kernel.org
Signed-off-by: Ruihan Li <lrh2000@....edu.cn>
---
 drivers/usb/core/devio.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/drivers/usb/core/devio.c b/drivers/usb/core/devio.c
index b4cf9e860..5067030b7 100644
--- a/drivers/usb/core/devio.c
+++ b/drivers/usb/core/devio.c
@@ -235,7 +235,7 @@ static int usbdev_mmap(struct file *file, struct vm_area_struct *vma)
 	size_t size = vma->vm_end - vma->vm_start;
 	void *mem;
 	unsigned long flags;
-	dma_addr_t dma_handle;
+	dma_addr_t dma_handle = DMA_MAPPING_ERROR;
 	int ret;

 	ret = usbfs_increase_memory_usage(size + sizeof(struct usb_memory));
@@ -265,7 +265,13 @@ static int usbdev_mmap(struct file *file, struct vm_area_struct *vma)
 	usbm->vma_use_count = 1;
 	INIT_LIST_HEAD(&usbm->memlist);

-	if (hcd->localmem_pool || !hcd_uses_dma(hcd)) {
+	/* In DMA-unavailable cases, hcd_buffer_alloc_pages allocates
+	 * normal pages and assigns DMA_MAPPING_ERROR to dma_handle. Check
+	 * whether we are in such cases, and then use remap_pfn_range (or
+	 * dma_mmap_coherent) to map normal (or DMA) pages into the user
+	 * space, respectively.
+	 */
+	if (dma_handle == DMA_MAPPING_ERROR) {
 		if (remap_pfn_range(vma, vma->vm_start,
 				    virt_to_phys(usbm->mem) >> PAGE_SHIFT,
 				    size, vma->vm_page_prot) < 0) {
-- 
2.40.1