linux-kernel - Re: [PATCH] Hibernate: check unsafe page should not in e820 reserved region

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Date:	Mon, 04 Aug 2014 14:42:32 +0200
From:	Takashi Iwai <tiwai@...e.de>
To:	"Lee, Chun-Yi" <joeyli.kernel@...il.com>
Cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
	linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
	"Lee, Chun-Yi" <jlee@...e.com>
Subject: Re: [PATCH] Hibernate: check unsafe page should not in e820 reserved region

At Mon,  4 Aug 2014 18:33:16 +0800,
Lee, Chun-Yi wrote:
> 
> When the machine doesn't well handle the e820 persistent when hibernate
> resuming, then it may causes 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 regsion: [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.
> 
> Cc: "Rafael J. Wysocki" <rjw@...ysocki.net>
> Cc: Len Brown <len.brown@...el.com>
> Cc: Pavel Machek <pavel@....cz>
> Signed-off-by: Lee, Chun-Yi <jlee@...e.com>
> ---
>  kernel/power/snapshot.c | 24 +++++++++++++++++++++++-
>  1 file changed, 23 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/power/snapshot.c b/kernel/power/snapshot.c
> index 98c3b34..e6db5a8 100644
> --- a/kernel/power/snapshot.c
> +++ b/kernel/power/snapshot.c
> @@ -730,6 +730,28 @@ static void mark_nosave_pages(struct memory_bitmap *bm)
>  	}
>  }
>  
> +static bool is_nosave_page(unsigned long pfn)
> +{
> +	struct nosave_region *region;
> +
> +	if (list_empty(&nosave_regions))
> +		return 0;

Just a nitpicking: this should be "false" for consistency.
But, looking further at the code:

> +
> +	list_for_each_entry(region, &nosave_regions, list) {
> +		if (pfn >= region->start_pfn && pfn < region->end_pfn) {
> +			pr_err("PM: %#010llx in e820 nosave regsion: "
> +			       "[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;

I think the above empty check can be removed completely.


Takashi
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