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

[HORIGUCHI NAOYA(堀口 直也)]

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