linux-kernel - Re: [PATCH -next v4 2/3] x86/mce: rename MCE_IN_KERNEL_COPYIN to MCE_IN_KERNEL_COPY

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Date: Fri, 2 Feb 2024 15:51:12 +0800
From: Tong Tiangen <tongtiangen@...wei.com>
To: Borislav Petkov <bp@...en8.de>
CC: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
	<wangkefeng.wang@...wei.com>, Dave Hansen <dave.hansen@...ux.intel.com>,
	<x86@...nel.org>, "H. Peter Anvin" <hpa@...or.com>, Tony Luck
	<tony.luck@...el.com>, Andy Lutomirski <luto@...nel.org>, Peter Zijlstra
	<peterz@...radead.org>, Andrew Morton <akpm@...ux-foundation.org>, Naoya
 Horiguchi <naoya.horiguchi@....com>, <linux-kernel@...r.kernel.org>,
	<linux-edac@...r.kernel.org>, <linux-mm@...ck.org>, Guohanjun
	<guohanjun@...wei.com>
Subject: Re: [PATCH -next v4 2/3] x86/mce: rename MCE_IN_KERNEL_COPYIN to
 MCE_IN_KERNEL_COPY_MC



在 2024/2/1 22:20, Borislav Petkov 写道:
> On Thu, Feb 01, 2024 at 07:37:25PM +0800, Tong Tiangen wrote:
>> 在 2024/1/31 15:02, Borislav Petkov 写道:
>>> On Thu, Jan 11, 2024 at 09:55:47PM +0800, Tong Tiangen wrote:
>>>> Currently, there are some kernel memory copy scenarios is also mc safe
>>>> which use copy_mc_to_kernel() or copy_mc_user_highpage().
>>>
>>> Both of those end up in copy_mc_enhanced_fast_string() which does
>>> EX_TYPE_DEFAULT_MCE_SAFE.
>>
>> OK, how about this commit msg change? :)
>>
>> Currently, there are some kernel memory copy scenarios is also mc safe
>> which use copy_mc_to_kernel() or copy_mc_user_highpage(), **both of those
>> end up in copy_mc_enhanced_fast_string() or copy_mc_fragile() which does
>> EX_TYPE_DEFAULT_MCE_SAFE.**
>>
>> In these scenarios, posion pages need to be isolated too. Therefore, a
>> macro similar to MCE_IN_KERNEL_COPYIN is required. For this reason, we
>> can rename MCE_IN_KERNEL_COPYIN to MCE_IN_KERNEL_COPY_MC, the new macro
>> can be applied to both user-to-kernel mc safe copy and kernel-to-kernel
>> mc safe copy.
> 
> Maybe my question wasn't clear: why is that renaming churn needed at
> all? What are you "fixing" here?
> 
> What is the problem that you're encountering which needs fixing?

This patch is a prepare patch and the next patch is a fix patch, the
complete logic of the two patches is as follows:

The problem i'm encountering:
-------------------------------
In the x86 mce processing, error_context() setting macro
MCE_IN_KERNEL_COPYIN to identify copy from user(user-to-kernel copy) for
fixup_type EX_TYPE_UACCESS.

Then do_machine_check() uses macro MCE_IN_KERNEL_COPYIN to isolate
posion page in memory_failure().

Currently, there are some kernel memory copy scenarios is also mc safe
which use copy_mc_to_kernel() or copy_mc_user_highpage(), these kernel-
to-kernel copy use fixup_type EX_TYPE_DEFAULT_MCE_SAFE. In these
scenarios, posion pages need to be isolated too and the current
implementation is to actively call memory_failure_queue() when the copy
fails.

Calling memory_failure_queue() separately is not a good implementation,
call it uniformly in do_machine_check() is more reasonable.

Solution:
----------
A macro similar to MCE_IN_KERNEL_COPYIN is required, so we can rename
MCE_IN_KERNEL_COPYIN to MCE_IN_KERNEL_COPY_MC, the new macro can be
applied to both user-to-kernel mc safe copy and kernel-to-kernel mc safe
copy, in error_context()，we can set MCE_IN_KERNEL_COPY_MC for both
fixup_type EX_TYPE_UACCESS and EX_TYPE_DEFAULT_MCE_SAFE.



Do you think it's clear to say so and then we can merge the two patches
to make the complete logic clearer in commit msg ?

Many thanks.
Tong.

> 
> Thx.
>