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Sender: Ingo Molnar <mingo.kernel.org@gmail.com>
Date:   Mon, 2 Oct 2023 21:06:12 +0200
From:   Ingo Molnar <mingo@kernel.org>
To:     Zhiquan Li <zhiquan1.li@intel.com>
Cc:     x86@kernel.org, linux-edac@vger.kernel.org,
        linux-kernel@vger.kernel.org, patches@lists.linux.dev,
        bp@alien8.de, tony.luck@intel.com, naoya.horiguchi@nec.com,
        Youquan Song <youquan.song@intel.com>
Subject: Re: [PATCH RESEND v2] x86/mce: Set PG_hwpoison page flag to avoid
 the capture kernel panic
Message-ID: <ZRsUpM/XtPAE50Rm@gmail.com>
References: <20230914030539.1622477-1-zhiquan1.li@intel.com>
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In-Reply-To: <20230914030539.1622477-1-zhiquan1.li@intel.com>
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* Zhiquan Li <zhiquan1.li@intel.com> wrote:

> Kdump can exclude the HWPosion page to avoid touch the error page
> again, the prerequisite is the PG_hwpoison page flag is set.
> However, for some MCE fatal error cases, there is no opportunity
> to queue a task for calling memory_failure(), as a result,
> the capture kernel touches the error page again and panics.
> 
> Add function mce_set_page_hwpoison_now() which marks a page as
> HWPoison before kernel panic() for MCE error, so that the dump
> program can check and skip the error page and prevent the capture
> kernel panic.
> 
> [Tony: Changed TestSetPageHWPoison() to SetPageHWPoison()]
> 
> Co-developed-by: Youquan Song <youquan.song@intel.com>
> Signed-off-by: Youquan Song <youquan.song@intel.com>
> Signed-off-by: Zhiquan Li <zhiquan1.li@intel.com>
> Signed-off-by: Tony Luck <tony.luck@intel.com>
> Reviewed-by: Naoya Horiguchi <naoya.horiguchi@nec.com>
> 
> ---
> V2 RESEND notes:
> - No changes on this, just rebasing as v6.6-rc1 is out.
> - Added the tag from Naoya.
>   Link: https://lore.kernel.org/all/20230719211625.298785-1-tony.luck@intel.com/#t
> 
> Changes since V1:
> - Revised the commit message as per Naoya's suggestion.
> - Replaced "TODO" comment in code with comments based on mailing list
>   discussion on the lack of value in covering other page types.
>   Link: https://lore.kernel.org/all/20230127015030.30074-1-tony.luck@intel.com/
> ---
>  arch/x86/kernel/cpu/mce/core.c | 18 ++++++++++++++++++
>  1 file changed, 18 insertions(+)
> 
> diff --git a/arch/x86/kernel/cpu/mce/core.c b/arch/x86/kernel/cpu/mce/core.c
> index 6f35f724cc14..2725698268f3 100644
> --- a/arch/x86/kernel/cpu/mce/core.c
> +++ b/arch/x86/kernel/cpu/mce/core.c
> @@ -156,6 +156,22 @@ void mce_unregister_decode_chain(struct notifier_block *nb)
>  }
>  EXPORT_SYMBOL_GPL(mce_unregister_decode_chain);
>  
> +/*
> + * Kdump can exclude the HWPosion page to avoid touch the error page again,
> + * the prerequisite is the PG_hwpoison page flag is set. However, for some
> + * MCE fatal error cases, there are no opportunity to queue a task
> + * for calling memory_failure(), as a result, the capture kernel panics.
> + * This function marks the page as HWPoison before kernel panic() for MCE.
> + */

The English in this commit is *atrocious*, both in the changelog and in
the comments - how on Earth did 'Posion' typo and half a dozen other typos
and bad grammar survive ~3 iterations and a Reviewed-by tag??

The version below fixes up the worst, but I suspect that's not the only problem
with this patch...

Thanks,

	Ingo

================>
From: Zhiquan Li <zhiquan1.li@intel.com>
Date: Thu, 14 Sep 2023 11:05:39 +0800
Subject: [PATCH] x86/mce: Set PG_hwpoison page flag to avoid the capture kernel panic

Kdump can exclude the HWPoison page to avoid touching the error page
again, the prerequisite is the PG_hwpoison page flag is set.

However, for some MCE fatal error cases, there is no opportunity
to queue a task for calling memory_failure(), and as a result,
the capture kernel touches the error page again and panics.

Add the mce_set_page_hwpoison_now() function, which marks a page as
HWPoison before kernel panic() for MCE error, so that the dump
program can check and skip the error page and prevent the capture
kernel panic.

[ Tony: Changed TestSetPageHWPoison() to SetPageHWPoison() ]
[ mingo: Fixed the comments & changelog ]

Co-developed-by: Youquan Song <youquan.song@intel.com>
Signed-off-by: Youquan Song <youquan.song@intel.com>
Signed-off-by: Zhiquan Li <zhiquan1.li@intel.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Naoya Horiguchi <naoya.horiguchi@nec.com>
Cc: Borislav Petkov <bp@alien8.de>
Link: https://lore.kernel.org/all/20230719211625.298785-1-tony.luck@intel.com/#t
---
 arch/x86/kernel/cpu/mce/core.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/arch/x86/kernel/cpu/mce/core.c b/arch/x86/kernel/cpu/mce/core.c
index 6f35f724cc14..1a14e8233c5a 100644
--- a/arch/x86/kernel/cpu/mce/core.c
+++ b/arch/x86/kernel/cpu/mce/core.c
@@ -156,6 +156,22 @@ void mce_unregister_decode_chain(struct notifier_block *nb)
 }
 EXPORT_SYMBOL_GPL(mce_unregister_decode_chain);
 
+/*
+ * Kdump can exclude the HWPoison page to avoid touching the error page again,
+ * the prerequisite is that the PG_hwpoison page flag is set. However, for some
+ * MCE fatal error cases, there is no opportunity to queue a task
+ * for calling memory_failure(), and as a result, the capture kernel panics.
+ * This function marks the page as HWPoison before kernel panic() for MCE.
+ */
+static void mce_set_page_hwpoison_now(unsigned long pfn)
+{
+	struct page *p;
+
+	p = pfn_to_online_page(pfn);
+	if (p)
+		SetPageHWPoison(p);
+}
+
 static void __print_mce(struct mce *m)
 {
 	pr_emerg(HW_ERR "CPU %d: Machine Check%s: %Lx Bank %d: %016Lx\n",
@@ -286,6 +302,8 @@ static noinstr void mce_panic(const char *msg, struct mce *final, char *exp)
 	if (!fake_panic) {
 		if (panic_timeout == 0)
 			panic_timeout = mca_cfg.panic_timeout;
+		if (final && (final->status & MCI_STATUS_ADDRV))
+			mce_set_page_hwpoison_now(final->addr >> PAGE_SHIFT);
 		panic(msg);
 	} else
 		pr_emerg(HW_ERR "Fake kernel panic: %s\n", msg);