Re: [PATCH v2 3/5] kernel/power: allow hibernation with page_poison sanity checking

From: David Hildenbrand
Date: Wed Nov 11 2020 - 10:42:58 EST


On 03.11.20 16:22, Vlastimil Babka wrote:
Page poisoning used to be incompatible with hibernation, as the state of
poisoned pages was lost after resume, thus enabling CONFIG_HIBERNATION forces
CONFIG_PAGE_POISONING_NO_SANITY. For the same reason, the poisoning with zeroes
variant CONFIG_PAGE_POISONING_ZERO used to disable hibernation. The latter
restriction was removed by commit 1ad1410f632d ("PM / Hibernate: allow
hibernation with PAGE_POISONING_ZERO") and similarly for init_on_free by commit
18451f9f9e58 ("PM: hibernate: fix crashes with init_on_free=1") by making sure
free pages are cleared after resume.

We can use the same mechanism to instead poison free pages with PAGE_POISON
after resume. This covers both zero and 0xAA patterns. Thus we can remove the
Kconfig restriction that disables page poison sanity checking when hibernation
is enabled.

Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>
Cc: "Rafael J. Wysocki" <rjw@xxxxxxxxxxxxx>
Cc: Len Brown <len.brown@xxxxxxxxx>
Cc: Pavel Machek <pavel@xxxxxx>
Cc: <linux-pm@xxxxxxxxxxxxxxx>
---
kernel/power/hibernate.c | 2 +-
kernel/power/power.h | 2 +-
kernel/power/snapshot.c | 14 ++++++++++----
mm/Kconfig.debug | 1 -
4 files changed, 12 insertions(+), 7 deletions(-)

diff --git a/kernel/power/hibernate.c b/kernel/power/hibernate.c
index 2fc7d509a34f..da0b41914177 100644
--- a/kernel/power/hibernate.c
+++ b/kernel/power/hibernate.c
@@ -326,7 +326,7 @@ static int create_image(int platform_mode)
if (!in_suspend) {
events_check_enabled = false;
- clear_free_pages();
+ clear_or_poison_free_pages();
}
platform_leave(platform_mode);
diff --git a/kernel/power/power.h b/kernel/power/power.h
index 24f12d534515..778bf431ec02 100644
--- a/kernel/power/power.h
+++ b/kernel/power/power.h
@@ -106,7 +106,7 @@ extern int create_basic_memory_bitmaps(void);
extern void free_basic_memory_bitmaps(void);
extern int hibernate_preallocate_memory(void);
-extern void clear_free_pages(void);
+extern void clear_or_poison_free_pages(void);
/**
* Auxiliary structure used for reading the snapshot image data and
diff --git a/kernel/power/snapshot.c b/kernel/power/snapshot.c
index 46b1804c1ddf..6b1c84afa891 100644
--- a/kernel/power/snapshot.c
+++ b/kernel/power/snapshot.c
@@ -1144,7 +1144,7 @@ void free_basic_memory_bitmaps(void)
pr_debug("Basic memory bitmaps freed\n");
}
-void clear_free_pages(void)
+void clear_or_poison_free_pages(void)
{
struct memory_bitmap *bm = free_pages_map;
unsigned long pfn;
@@ -1152,12 +1152,18 @@ void clear_free_pages(void)
if (WARN_ON(!(free_pages_map)))
return;
- if (IS_ENABLED(CONFIG_PAGE_POISONING_ZERO) || want_init_on_free()) {
+ if (page_poisoning_enabled() || want_init_on_free()) {
memory_bm_position_reset(bm);
pfn = memory_bm_next_pfn(bm);
while (pfn != BM_END_OF_MAP) {
- if (pfn_valid(pfn))
- clear_highpage(pfn_to_page(pfn));
+ if (pfn_valid(pfn)) {
+ struct page *page = pfn_to_page(pfn);

^ empty line missing. And at least I prefer to declare all variables in the function header.

I'd even suggest to move this into a separate function like

clear_or_poison_free_page(struct page *page)


+ if (page_poisoning_enabled_static())
+ kernel_poison_pages(page, 1);
+ else if (want_init_on_free())
+ clear_highpage(page);
+
+ }
pfn = memory_bm_next_pfn(bm);
}
diff --git a/mm/Kconfig.debug b/mm/Kconfig.debug
index 864f129f1937..c57786ad5be9 100644
--- a/mm/Kconfig.debug
+++ b/mm/Kconfig.debug
@@ -64,7 +64,6 @@ config PAGE_OWNER
config PAGE_POISONING
bool "Poison pages after freeing"
- select PAGE_POISONING_NO_SANITY if HIBERNATION
help
Fill the pages with poison patterns after free_pages() and verify
the patterns before alloc_pages. The filling of the memory helps


Unless I am missing something important, this should work! Thanks!

--
Thanks,

David / dhildenb