linux-kernel - [PATCH 2/3] PM / hibernate: avoid unsafe pages in e820 reserved regions

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Date:	Thu, 27 Aug 2015 15:06:11 +0800
From:	Chen Yu <yu.c.chen@...el.com>
To:	tglx@...utronix.de, mingo@...hat.com, rjw@...ysocki.net,
	pavel@....cz, hpa@...or.com
Cc:	len.brown@...el.com, yinghai@...nel.org, joeyli.kernel@...il.com,
	rui.zhang@...el.com, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH 2/3] PM / hibernate: avoid unsafe pages in e820 reserved regions

From: "Lee, Chun-Yi" <joeyli.kernel@...il.com>

When the machine doesn't well handle the e820 persistent when hibernate
resuming, then it may cause page fault when writing image to snapshot
buffer:

[   17.929495] BUG: unable to handle kernel paging request at ffff880069d4f000
[   17.933469] IP: [<ffffffff810a1cf0>] load_image_lzo+0x810/0xe40
[   17.933469] PGD 2194067 PUD 77ffff067 PMD 2197067 PTE 0
[   17.933469] Oops: 0002 [#1] SMP
...

The ffff880069d4f000 page is in e820 reserved region of resume boot
kernel:

[    0.000000] BIOS-e820: [mem 0x0000000069d4f000-0x0000000069e12fff] reserved
...
[    0.000000] PM: Registered nosave memory: [mem 0x69d4f000-0x69e12fff]

So snapshot.c mark the pfn to forbidden pages map. But, this
page is also in the memory bitmap in snapshot image because it's an
original page used by image kernel, so it will also mark as an
unsafe(free) page in prepare_image().

That means the page in e820 when resuming mark as "forbidden" and
"free", it causes get_buffer() treat it as an allocated unsafe page.
Then snapshot_write_next() return this page to load_image, load_image
writing content to this address, but this page didn't really allocated
. So, we got page fault.

Although the root cause is from BIOS, I think aggressive check and
significant message in kernel will better then a page fault for
issue tracking, especially when serial console unavailable.

This patch adds code in mark_unsafe_pages() for check does free pages in
nosave region. If so, then it print message and return fault to stop whole
S4 resume process:

[    8.166004] PM: Image loading progress:   0%
[    8.658717] PM: 0x6796c000 in e820 nosave region: [mem 0x6796c000-0x6796cfff]
[    8.918737] PM: Read 2511940 kbytes in 1.04 seconds (2415.32 MB/s)
[    8.926633] PM: Error -14 resuming
[    8.933534] PM: Failed to load hibernation image, recovering.

Signed-off-by: Lee, Chun-Yi <jlee@...e.com>
Signed-off-by: Chen Yu <yu.c.chen@...el.com>
---
 kernel/power/snapshot.c | 21 ++++++++++++++++++++-
 1 file changed, 20 insertions(+), 1 deletion(-)

diff --git a/kernel/power/snapshot.c b/kernel/power/snapshot.c
index 5235dd4..c24d5a2 100644
--- a/kernel/power/snapshot.c
+++ b/kernel/power/snapshot.c
@@ -955,6 +955,25 @@ static void mark_nosave_pages(struct memory_bitmap *bm)
 	}
 }
 
+static bool is_nosave_page(unsigned long pfn)
+{
+	struct nosave_region *region;
+
+	list_for_each_entry(region, &nosave_regions, list) {
+		if (pfn >= region->start_pfn && pfn < region->end_pfn) {
+			pr_err("PM: %#010llx in e820 nosave region: "
+			       "[mem %#010llx-%#010llx]\n",
+			       (unsigned long long) pfn << PAGE_SHIFT,
+			       (unsigned long long) region->start_pfn << PAGE_SHIFT,
+			       ((unsigned long long) region->end_pfn << PAGE_SHIFT)
+					- 1);
+			return true;
+		}
+	}
+
+	return false;
+}
+
 /**
  *	create_basic_memory_bitmaps - create bitmaps needed for marking page
  *	frames that should not be saved and free page frames.  The pointers
@@ -2023,7 +2042,7 @@ static int mark_unsafe_pages(struct memory_bitmap *bm)
 	do {
 		pfn = memory_bm_next_pfn(bm);
 		if (likely(pfn != BM_END_OF_MAP)) {
-			if (likely(pfn_valid(pfn)))
+			if (likely(pfn_valid(pfn)) && !is_nosave_page(pfn))
 				swsusp_set_page_free(pfn_to_page(pfn));
 			else
 				return -EFAULT;
-- 
1.8.4.2

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