On 2021/6/23 10:50, Al Viro wrote:

On Wed, Jun 23, 2021 at 10:39:31AM +0800, Chen Huang wrote:

quoted

Then when kernel handles the alignment_fault, it will not panic. As the
arm64 memory model spec said, when the address is not a multiple of the
element size, the access is unaligned. Unaligned accesses are allowed to
addresses marked as Normal, but not to Device regions. An unaligned access
to a Device region will trigger an exception (alignment fault).
	
do_alignment_fault
     do_bad_area
	__do_kernel_fault
            fixup_exception

But that fixup cann't handle the unaligned copy, so the
copy_page_from_iter_atomic returns 0 and traps in loop.

Looks like you need to fix your raw_copy_from_user(), then...
.

Exit loop when iov_iter_copy_from_user_atomic() returns 0.
This should solve the problem, too, and it's easier.

Thanks.
Xiaoming Ni





	

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