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Date: Wed, 23 Jun 2021 02:50:54 +0000
From: Al Viro <viro@zeniv.linux.org.uk>
To: Chen Huang <chenhuang5@huawei.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Stephen Rothwell <sfr@canb.auug.org.au>,
	"Matthew Wilcox (Oracle)" <willy@infradead.org>,
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Subject: Re: [BUG] arm64: an infinite loop in generic_perform_write()
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On Wed, Jun 23, 2021 at 10:39:31AM +0800, Chen Huang wrote:

> 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...