linux-kernel - Re: [PATCH v2] x86/mce: set MCE_IN_KERNEL

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Date:   Fri, 26 May 2023 09:09:52 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Kefeng Wang <wangkefeng.wang@...wei.com>
Cc:     tony.luck@...el.com, naoya.horiguchi@....com, tglx@...utronix.de,
        mingo@...hat.com, dave.hansen@...ux.intel.com, x86@...nel.org,
        akpm@...ux-foundation.org, linux-edac@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        jane.chu@...cle.com
Subject: Re: [PATCH v2] x86/mce: set MCE_IN_KERNEL_COPYIN for all MC-Safe Copy

On Fri, May 26, 2023 at 02:32:42PM +0800, Kefeng Wang wrote:
> The best way to fix them is set MCE_IN_KERNEL_COPYIN for MC-Safe Copy,
> then let the core do_machine_check() to isolate corrupted page instead
> of doing it one-by-one.

No, this whole thing is confused.

 * Indicates an MCE that happened in kernel space while copying data
 * from user.

#define MCE_IN_KERNEL_COPYIN

This is a very specific exception type: EX_TYPE_COPY which got added by

  278b917f8cb9 ("x86/mce: Add _ASM_EXTABLE_CPY for copy user access")

but Linus then removed all such user copy exception points in

  034ff37d3407 ("x86: rewrite '__copy_user_nocache' function")

So now that EX_TYPE_COPY never happens.

And what you're doing is lumping the handling for
EX_TYPE_DEFAULT_MCE_SAFE and EX_TYPE_FAULT_MCE_SAFE together and saying
that the MCE happened while copying data from user.

And XSTATE_OP() is one example where this is not really the case.

So no, this is not correct.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette