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[PATCH 0/2] Hibernate fixes for 'Fix memmap to be initialized for the entire section'

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  [PATCH 0/2] Hibernate fixes for 'Fix memmap to be initialized for the entire section' James Morse <james.morse@arm.com> - 2016-12-02 16:00 +0100
    [PATCH 2/2] arm64: hibernate: report nomap regions as being pfn_nosave James Morse <james.morse@arm.com> - 2016-12-02 16:00 +0100
    Re: [PATCH 0/2] Hibernate fixes for 'Fix memmap to be initialized for  the entire section' Ard Biesheuvel <ard.biesheuvel@linaro.org> - 2016-12-05 16:50 +0100
      Re: [PATCH 0/2] Hibernate fixes for 'Fix memmap to be initialized  for the entire section' Will Deacon <will.deacon@arm.com> - 2016-12-06 18:40 +0100
        Re: [PATCH 0/2] Hibernate fixes for 'Fix memmap to be initialized  for the entire section' Will Deacon <will.deacon@arm.com> - 2016-12-07 15:40 +0100

#1534996 — [PATCH 0/2] Hibernate fixes for 'Fix memmap to be initialized for the entire section'

Patch "arm64: mm: Fix memmap to be initialized for the entire section"
changes pfn_valid() in a way that breaks hibernate. These patches fix
hibernate, and provided struct page's are allocated for nomap pages,
can be applied before [0].

Hibernate core code belives 'valid' to mean "I can access this". It
uses pfn_valid() to test the page if the page is 'valid'.

pfn_valid() needs to be changed so that all struct pages in a numa
node have the same node-id. Currently 'nomap' pages are skipped, and
retain their pre-numa node-ids, which leads to a later BUG_ON().

These patches make hibernate's savable_page() take its escape route
via 'if (PageReserved(page) && pfn_is_nosave(pfn))'.


[0] https://lkml.org/lkml/2016/11/30/566

James Morse (2):
  arm64: mm: Mark nomap regions with the PG_reserved flag
  arm64: hibernate: report nomap regions as being pfn_nosave

 arch/arm64/kernel/hibernate.c |  6 +++++-
 arch/arm64/mm/init.c          | 14 ++++++++++++++
 2 files changed, 19 insertions(+), 1 deletion(-)

-- 
2.10.1

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#1535004 — [PATCH 2/2] arm64: hibernate: report nomap regions as being pfn_nosave

pfn_valid() needs to be changed so that all struct pages in a numa
node have the same node-id. Currently 'nomap' pages are skipped, and
retain their pre-numa node-ids, which leads to a later BUG_ON().

Once this change happens, hibernate's code code will try and
save/restore the nomap pages.

Add the memblock nomap regions to the ranges reported as being
'pfn_nosave' to the hibernate core code. This only works if all
pages in the nomap region are also marked with PG_reserved.

Signed-off-by: James Morse <james.morse@arm.com>
---
 arch/arm64/kernel/hibernate.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/kernel/hibernate.c b/arch/arm64/kernel/hibernate.c
index d55a7b09959b..9e901658a123 100644
--- a/arch/arm64/kernel/hibernate.c
+++ b/arch/arm64/kernel/hibernate.c
@@ -17,6 +17,7 @@
 #define pr_fmt(x) "hibernate: " x
 #include <linux/cpu.h>
 #include <linux/kvm_host.h>
+#include <linux/memblock.h>
 #include <linux/mm.h>
 #include <linux/pm.h>
 #include <linux/sched.h>
@@ -105,7 +106,10 @@ int pfn_is_nosave(unsigned long pfn)
 	unsigned long nosave_begin_pfn = virt_to_pfn(&__nosave_begin);
 	unsigned long nosave_end_pfn = virt_to_pfn(&__nosave_end - 1);
 
-	return (pfn >= nosave_begin_pfn) && (pfn <= nosave_end_pfn);
+	if ((pfn >= nosave_begin_pfn) && (pfn <= nosave_end_pfn))
+		return 1;
+
+	return !memblock_is_map_memory(pfn << PAGE_SHIFT);
 }
 
 void notrace save_processor_state(void)
-- 
2.10.1

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#1536185 — Re: [PATCH 0/2] Hibernate fixes for 'Fix memmap to be initialized for the entire section'

On 2 December 2016 at 14:49, James Morse <james.morse@arm.com> wrote:
> Patch "arm64: mm: Fix memmap to be initialized for the entire section"
> changes pfn_valid() in a way that breaks hibernate. These patches fix
> hibernate, and provided struct page's are allocated for nomap pages,
> can be applied before [0].
>
> Hibernate core code belives 'valid' to mean "I can access this". It
> uses pfn_valid() to test the page if the page is 'valid'.
>
> pfn_valid() needs to be changed so that all struct pages in a numa
> node have the same node-id. Currently 'nomap' pages are skipped, and
> retain their pre-numa node-ids, which leads to a later BUG_ON().
>
> These patches make hibernate's savable_page() take its escape route
> via 'if (PageReserved(page) && pfn_is_nosave(pfn))'.
>

This makes me feel slightly uneasy. Robert makes a convincing point,
but I wonder if we can expect more fallout from the ambiguity of
pfn_valid(). Now we are not only forced to assign non-existing (as far
as the OS is concerned) pages to the correct NUMA node, we also need
to set certain page flags.

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#1537160 — Re: [PATCH 0/2] Hibernate fixes for 'Fix memmap to be initialized for the entire section'

On Mon, Dec 05, 2016 at 03:42:14PM +0000, Ard Biesheuvel wrote:
> On 2 December 2016 at 14:49, James Morse <james.morse@arm.com> wrote:
> > Patch "arm64: mm: Fix memmap to be initialized for the entire section"
> > changes pfn_valid() in a way that breaks hibernate. These patches fix
> > hibernate, and provided struct page's are allocated for nomap pages,
> > can be applied before [0].
> >
> > Hibernate core code belives 'valid' to mean "I can access this". It
> > uses pfn_valid() to test the page if the page is 'valid'.
> >
> > pfn_valid() needs to be changed so that all struct pages in a numa
> > node have the same node-id. Currently 'nomap' pages are skipped, and
> > retain their pre-numa node-ids, which leads to a later BUG_ON().
> >
> > These patches make hibernate's savable_page() take its escape route
> > via 'if (PageReserved(page) && pfn_is_nosave(pfn))'.
> >
> 
> This makes me feel slightly uneasy. Robert makes a convincing point,
> but I wonder if we can expect more fallout from the ambiguity of
> pfn_valid(). Now we are not only forced to assign non-existing (as far
> as the OS is concerned) pages to the correct NUMA node, we also need
> to set certain page flags.

Yes, I really don't know how to proceed here. Playing whack-a-mole with
pfn_valid() users doesn't sounds like an improvement on the current
situation to me.

Robert -- if we leave pfn_valid() as it is, would a point-hack to
memmap_init_zone help, or do you anticipate other problems?

Will

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#1537782 — Re: [PATCH 0/2] Hibernate fixes for 'Fix memmap to be initialized for the entire section'

On Wed, Dec 07, 2016 at 10:06:38AM +0100, Robert Richter wrote:
> On 06.12.16 17:38:11, Will Deacon wrote:
> > On Mon, Dec 05, 2016 at 03:42:14PM +0000, Ard Biesheuvel wrote:
> > > On 2 December 2016 at 14:49, James Morse <james.morse@arm.com> wrote:
> > > > Patch "arm64: mm: Fix memmap to be initialized for the entire section"
> > > > changes pfn_valid() in a way that breaks hibernate. These patches fix
> > > > hibernate, and provided struct page's are allocated for nomap pages,
> > > > can be applied before [0].
> > > >
> > > > Hibernate core code belives 'valid' to mean "I can access this". It
> > > > uses pfn_valid() to test the page if the page is 'valid'.
> > > >
> > > > pfn_valid() needs to be changed so that all struct pages in a numa
> > > > node have the same node-id. Currently 'nomap' pages are skipped, and
> > > > retain their pre-numa node-ids, which leads to a later BUG_ON().
> > > >
> > > > These patches make hibernate's savable_page() take its escape route
> > > > via 'if (PageReserved(page) && pfn_is_nosave(pfn))'.
> > > >
> > > 
> > > This makes me feel slightly uneasy. Robert makes a convincing point,
> > > but I wonder if we can expect more fallout from the ambiguity of
> > > pfn_valid(). Now we are not only forced to assign non-existing (as far
> > > as the OS is concerned) pages to the correct NUMA node, we also need
> > > to set certain page flags.
> > 
> > Yes, I really don't know how to proceed here. Playing whack-a-mole with
> > pfn_valid() users doesn't sounds like an improvement on the current
> > situation to me.
> > 
> > Robert -- if we leave pfn_valid() as it is, would a point-hack to
> > memmap_init_zone help, or do you anticipate other problems?
> 
> I would suggest to fix the hibernation code as I commented on before
> to use pfn_is_nosave() that defaults to pfn_valid() but uses memblock_
> is_nomap() for arm64. Let's just fix it and see if no other issues
> arise. I am trying to send a patch for this until tomorrow.

I'd rather not use mainline as a guinea pig like this, since I'd be very
surprised if other places don't break given the scope for different
interpretations of pfn_valid.

> I am also going to see how early_pfn_valid() could be redirected to
> use memblock_is_nomap() on arm64. That would "quick fix" the problem,
> though I rather prefer to go further with the current solution.

I don't like either of them, but early_pfn_valid is easier to revert so
let's go with that.

Will

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