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Date: Mon, 1 Apr 2024 11:41:56 +0800
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Subject: Re: [PATCH -next v5 2/3] x86/mce: set MCE_IN_KERNEL_COPYIN for
 DEFAULT_MCE_SAFE exception
To: Borislav Petkov <bp@alien8.de>
CC: Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>,
	<wangkefeng.wang@huawei.com>, Dave Hansen <dave.hansen@linux.intel.com>,
	<x86@kernel.org>, "H. Peter Anvin" <hpa@zytor.com>, Tony Luck
	<tony.luck@intel.com>, Andy Lutomirski <luto@kernel.org>, Peter Zijlstra
	<peterz@infradead.org>, Andrew Morton <akpm@linux-foundation.org>, Naoya
 Horiguchi <naoya.horiguchi@nec.com>, <linux-kernel@vger.kernel.org>,
	<linux-edac@vger.kernel.org>, <linux-mm@kvack.org>, Guohanjun
	<guohanjun@huawei.com>
References: <20240204082627.3892816-1-tongtiangen@huawei.com>
 <20240204082627.3892816-3-tongtiangen@huawei.com>
 <20240207122942.GRZcN3tqWkV-WE-pak@fat_crate.local>
 <100198dd-320f-68e6-9c09-210620940a74@huawei.com>
 <20240327220511.GCZgSYF6lJ3U1CaKV0@fat_crate.local>
From: Tong Tiangen <tongtiangen@huawei.com>
In-Reply-To: <20240327220511.GCZgSYF6lJ3U1CaKV0@fat_crate.local>
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在 2024/3/28 6:05, Borislav Petkov 写道:
> On Sun, Feb 18, 2024 at 06:08:14PM +0800, Tong Tiangen wrote:
>> 1. The copy_mc_to_kernel() is used in the coredump, KSM, and COW
>> scenarios, in these scenarios, the src mem stores the user data and the
>> kernel use kernel address to access the src mem(using kmap()).
>>
>> 2. the src mem of copy_mc_to_user() is currently only used by the DAX:
> 
> You mean just because it currently is used somewhere which probably is
> ok - no clue what DAX does - and even if the source address is still
> *kernel* memory and even at the danger that someone else might use it in
> the future and think the handling on a potential #MC is ok, you're still
> arguing that this is the right thing to do perhaps because it fits your
> use case?!
> 
> Sorry Tiangen, not gonna happen.
> 

I left the office last week and felt sorry for the lateness of the
reply.

You are right. Our current processing is based on "experience" rather
than interface constraints.

is_copy_from_user() determines whether a user is a "copy user" based on
fault_in_kernel_space(). Therefore, it returns false for
copy_mc_to_kernel()/copy_mc_to_user(). As a result, MCE_IN_KERNEL_COPYIN
cannot be set in error_context().

Comprehensive consideration of all factors, it is better to manually
call memory_failure_queue() to handle this problem case by case.

Finally, do we consider accepting only the patch 1/3 ?

Thanks,
Tong.