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SubjectRe: [PATCH] uio: Fix bus error that access memory mapped by physical
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On 2021/6/23 下午5:25, Greg KH wrote:
> A: Because it messes up the order in which people normally read text.
> Q: Why is top-posting such a bad thing?
> A: Top-posting.
> Q: What is the most annoying thing in e-mail?
>
> A: No.
> Q: Should I include quotations after my reply?
>
> http://daringfireball.net/2007/07/on_top
>
> On Wed, Jun 23, 2021 at 04:49:16PM +0800, wubian wrote:
>> First,thanks for your reply
>>
>> I haven’t found this problem on the x86 platform. I only found it on arm64.
>> I used gdb to track memset and found that the bus error in
>> glibc/sysdeps/aarch64/memset.S: dc zva, dst; reference "Architecture
>> Reference ManualArmv8, for Armv8-A architecture profile" manual found that
>> the dc assembly instruction(performance optimization) is related to the
>> operation of the cache, that is to say, there is a bus error in the
>> operation of the cache, and then check the "ARM Cortex-A Series Programmer's
>> Guide for ARMv8-A " manual, found that the armv8 architecture cache has data
>> cache and write buffer, and there are two operation modes write-back and
>> write-through, write operations in these two modes, the data flow will pass
>> through the write buffer, and pgprot_noncached will prohibit data Cache and
>> write buffer, this causes the dc command in memset to fail (bus error), and
>> pgprot_writecombine does not prohibit write buffer, so the dc command in
>> memset is successfully operated when pgprot_writecombine is used.
>
> Are you sure this is not just a specific hardware platform issue? Are
> you sure this is going to be correct for _ALL_ arm64 systems?
>
> Perhaps get the arm64 developers to agree with what is happening here as
> this is the first time anyone has reported this problem.
>
> What specific platform are you using that this issue happens on?
>
> thanks,
>
> greg k-h
>
>

I apologize for the kernel mail reply format problem, I will pay
attention to it in the future.

I only found this problem on Huawei Kunpeng 920 cpu at present, and
found that some people
have raised similar problems on the Internet.
link:https://github.com/ikwzm/udmabuf/issues/31

@Catalin Marinas @Will Deacon Has anyone reported a similar problem on
the arm64 platform?


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