linux-kernel - Re: [PATCH] x86/mce: Set PG_hwpoison page flag to avoid the capture kernel panic

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Date:   Tue, 31 Jan 2023 04:50:12 +0000
From:   HORIGUCHI NAOYA(堀口　直也) 
        <naoya.horiguchi@....com>
To:     "Luck, Tony" <tony.luck@...el.com>
CC:     Borislav Petkov <bp@...en8.de>, "x86@...nel.org" <x86@...nel.org>,
        "linux-edac@...r.kernel.org" <linux-edac@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "patches@...ts.linux.dev" <patches@...ts.linux.dev>,
        "Li, Zhiquan1" <zhiquan1.li@...el.com>,
        "Song, Youquan" <youquan.song@...el.com>
Subject: Re: [PATCH] x86/mce: Set PG_hwpoison page flag to avoid the capture
 kernel panic

On Mon, Jan 30, 2023 at 07:21:15PM +0000, Luck, Tony wrote:
> > Although I'm not sure that SGX memory or PMEM pages are expected to be
> > included in kdump, but simply setting PageHWPoison does not work for them?
> > (Maybe that depends on how kdump handles these types of memory.)
> 
> SGX/TDX pages can't be dumped. They are encrypted with no way for kdump to
> get the key.
> 
> PMEM seems pointless (but I don't know what kdump does here).
> 
> > As for HugeTLB, kdump utility should parse the struct page and be aware of
> > HugeTLB pages, so maybe setting PageHWPoison on the head page could work.
> 
> Or maybe kdump can take not of the PageHWPoison flag on the sub-page of the
> huge page? It depends on whether there is any benefit to the dump to include the
> not-poisoned parts of a huge page.

I think that many kdump users filter out HugeTLB pages (setting dump_level
to filter "User pages") to reduce the size of kdump.  User pages are not
much helpful to investigate kernel problems, so filtering all sub-pages in
hwpoisoned hugepage seems to me not so harmful.

I don't say that saving healthy subpages has no benefit, but I don't know
much about usecases where user pages in kdump file help.

Thanks,
Naoya Horiguchi