linux-kernel - [PATCH] uio: Fix bus error that access memory mapped by physical

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Date:   Wed, 23 Jun 2021 14:52:14 +0800
From:   wubian <wubian@...ontech.com>
To:     gregkh@...uxfoundation.org
Cc:     linux-kernel@...r.kernel.org, wubian <wubian@...ontech.com>
Subject: [PATCH] uio: Fix bus error that access memory mapped by physical

On the arm64, register the uio driver and map a physical space
on the pci device to user space, then use memset write data to
the address space, a bus error will occur. This error is due to
the dc instruction(cache operation) used in the assembly of memset,
uio mapping physical memory will call pgprot_noncached() to set
non-cached and non-buffered, while pgprot_writecombine() has fewer
restrictions. It does not prohibit write buffer, so replacing
pgprot_noncached() with pgprot_writecombine() can solve this problem.

Signed-off-by: wubian <wubian@...ontech.com>
---
 drivers/uio/uio.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/uio/uio.c b/drivers/uio/uio.c
index ea96e319c8a0..09b04b20fa30 100644
--- a/drivers/uio/uio.c
+++ b/drivers/uio/uio.c
@@ -739,7 +739,11 @@ static int uio_mmap_physical(struct vm_area_struct *vma)

 	vma->vm_ops = &uio_physical_vm_ops;
 	if (idev->info->mem[mi].memtype == UIO_MEM_PHYS)
+#if defined(CONFIG_ARM64)
+		vma->vm_page_prot = pgprot_writecombine(vma->vm_page_prot);
+#else
 		vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
+#endif

 	/*
 	 * We cannot use the vm_iomap_memory() helper here,
-- 
2.20.1