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

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Date:   Thu, 25 May 2023 10:18:24 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Kefeng Wang <wangkefeng.wang@...wei.com>,
        Tony Luck <tony.luck@...el.com>,
        Borislav Petkov <bp@...en8.de>,
        Naoya Horiguchi <naoya.horiguchi@....com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        Andrew Morton <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] x86/mce: set MCE_IN_KERNEL_COPYIN for all MC-Safe Copy

On 5/7/23 19:22, Kefeng Wang wrote:
> Both EX_TYPE_FAULT_MCE_SAFE and EX_TYPE_DEFAULT_MCE_SAFE exception
> fixup types are used to identify fixups which allow in kernel #MC
> recovery, that is the Machine Check Safe Copy.
> 
> For now, the MCE_IN_KERNEL_COPYIN flag is only set for EX_TYPE_COPY
> and EX_TYPE_UACCESS when copy from user, and corrupted page is
> isolated in this case, for MC-safe copy, memory_failure() is not
> always called, some places, like __wp_page_copy_user, copy_subpage,
> copy_user_gigantic_page and ksm_might_need_to_copy manually call
> memory_failure_queue() to cope with such unhandled error pages,
> recently coredump hwposion recovery support[1] is asked to do the
> same thing, and there are some other already existed MC-safe copy
> scenarios, eg, nvdimm, dm-writecache, dax, which has similar issue.

That has to set some kind of record for run-on sentences.  Could you
please try to rewrite this coherently?

> The best way to fix them is set MCE_IN_KERNEL_COPYIN to MCE_SAFE
> exception, then kill_me_never() will be queued to call memory_failure()
> in do_machine_check() to isolate corrupted page, which avoid calling
> memory_failure_queue() after every MC-safe copy return.

Could you try to send a v2 of this with a clear problem statement?

What is the end user visible effect of the problem and of your solution?