From: Mike Rapoport <rppt@kernel.org>
To: David Hildenbrand <david@redhat.com>
Cc: "Edgecombe, Rick P" <rick.p.edgecombe@intel.com>,
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Subject: Re: [PATCH 0/4] arch, mm: improve robustness of direct map manipulation
Date: Wed, 28 Oct 2020 13:09:45 +0200 [thread overview]
Message-ID: <20201028110945.GE1428094@kernel.org> (raw)
In-Reply-To: <e5fc62b6-f644-4ed5-de5b-ffd8337861e4@redhat.com>
On Tue, Oct 27, 2020 at 09:46:35AM +0100, David Hildenbrand wrote:
> On 27.10.20 09:38, Mike Rapoport wrote:
> > On Mon, Oct 26, 2020 at 06:05:30PM +0000, Edgecombe, Rick P wrote:
> >
> > > Beyond whatever you are seeing, for the latter case of new things
> > > getting introduced to an interface with hidden dependencies... Another
> > > edge case could be a new caller to set_memory_np() could result in
> > > large NP pages. None of the callers today should cause this AFAICT, but
> > > it's not great to rely on the callers to know these details.
> > A caller of set_memory_*() or set_direct_map_*() should expect a failure
> > and be ready for that. So adding a WARN to safe_copy_page() is the first
> > step in that direction :)
> >
>
> I am probably missing something important, but why are we saving/restoring
> the content of pages that were explicitly removed from the identity mapping
> such that nobody will access them?
Actually, we should not be saving/restoring free pages during
hibernation as there are several calls to mark_free_pages() that should
exclude the free pages from the snapshot. I've tried to find why the fix
that maps/unmaps a page to save it was required at the first place, but
I could not find bug reports.
The closest I've got is an email from Rafael that asked to update
"hibernate: handle DEBUG_PAGEALLOC" patch:
https://lore.kernel.org/linux-pm/200802200133.44098.rjw@sisk.pl/
Could it be that safe_copy_page() tries to workaround a non-existent
problem?
--
Sincerely yours,
Mike.
next prev parent reply other threads:[~2020-10-29 0:34 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-25 10:15 [PATCH 0/4] arch, mm: improve robustness of direct map manipulation Mike Rapoport
2020-10-25 10:15 ` [PATCH 1/4] mm: introduce debug_pagealloc_map_pages() helper Mike Rapoport
2020-10-26 11:05 ` David Hildenbrand
2020-10-26 11:54 ` Mike Rapoport
2020-10-26 11:55 ` David Hildenbrand
2020-10-25 10:15 ` [PATCH 2/4] PM: hibernate: improve robustness of mapping pages in the direct map Mike Rapoport
2020-10-26 0:38 ` Edgecombe, Rick P
2020-10-26 9:15 ` Mike Rapoport
2020-10-26 18:57 ` Edgecombe, Rick P
2020-10-27 8:49 ` Mike Rapoport
2020-10-27 22:44 ` Edgecombe, Rick P
2020-10-28 9:41 ` Mike Rapoport
2020-10-27 1:10 ` Edgecombe, Rick P
2020-10-28 21:15 ` Edgecombe, Rick P
2020-10-29 7:54 ` Mike Rapoport
2020-10-29 23:19 ` Edgecombe, Rick P
2020-11-01 17:02 ` Mike Rapoport
2020-10-25 10:15 ` [PATCH 3/4] arch, mm: restore dependency of __kernel_map_pages() of DEBUG_PAGEALLOC Mike Rapoport
2020-10-25 10:15 ` [PATCH 4/4] arch, mm: make kernel_page_present() always available Mike Rapoport
2020-10-26 0:54 ` Edgecombe, Rick P
2020-10-26 9:31 ` Mike Rapoport
2020-10-26 1:13 ` [PATCH 0/4] arch, mm: improve robustness of direct map manipulation Edgecombe, Rick P
2020-10-26 9:05 ` Mike Rapoport
2020-10-26 18:05 ` Edgecombe, Rick P
2020-10-27 8:38 ` Mike Rapoport
2020-10-27 8:46 ` David Hildenbrand
2020-10-27 9:47 ` Mike Rapoport
2020-10-27 10:34 ` David Hildenbrand
2020-10-28 11:09 ` Mike Rapoport [this message]
2020-10-28 11:17 ` David Hildenbrand
2020-10-28 12:22 ` Mike Rapoport
2020-10-28 18:31 ` Edgecombe, Rick P
2020-10-28 11:20 ` Will Deacon
2020-10-28 11:30 ` Mike Rapoport
2020-10-28 21:03 ` Edgecombe, Rick P
2020-10-29 8:12 ` Mike Rapoport
2020-10-29 23:19 ` Edgecombe, Rick P
2020-10-29 8:15 ` David Hildenbrand
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