NetBSD Problem Report #49869

From mlelstv@twitty.1st.de  Sat May  2 07:48:27 2015
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Date: Sat,  2 May 2015 09:48:17 +0200 (CEST)
From: mlelstv@serpens.de
Reply-To: mlelstv@serpens.de
To: gnats-bugs@NetBSD.org
Subject: Xen DomU fails to crash dump
X-Send-Pr-Version: 3.95

>Number:         49869
>Category:       port-xen
>Synopsis:       Xen DomU fails to crash dump
>Confidential:   no
>Severity:       serious
>Priority:       low
>Responsible:    port-xen-maintainer
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sat May 02 07:50:00 +0000 2015
>Last-Modified:  Sun May 03 23:30:01 +0000 2015
>Originator:     Michael van Elst
>Release:        NetBSD 7.99.13
>Organization:
--
                                Michael van Elst
Internet: mlelstv@serpens.de
                                "A potential Snark may lurk in every tree."
>Environment:


System: NetBSD test3.local 7.99.13 NetBSD 7.99.13 (XEN3PAE_DOMU.201505020340Z) #0: Sat May 2 06:01:27 UTC 2015 builds@b48.netbsd.org:/home/builds/ab/HEAD/i386/201505020340Z-obj/home/source/ab/HEAD/src/sys/arch/i386/compile/XEN3PAE_DOMU i386
Architecture: i386
Machine: i386
>Description:
Neither a i386 nor a amd64 DomU are able to dump core after a system
panic.

amd64 provides an empty memory map (dumpsize = 0) to the dump functions.
These will then just abort with the message "not possible".

i386 panics when you try to run the 'sync' command in ddb.

db{0}> sync

dumping to dev 142,1 offset 16431
dump fatal page fault in supervisor mode
trap type 6 code 2 eip c01558ed cs 9 eflags 10202 cr2 e7acbfff ilevel 8 esp c05c99c0
curlwp 0xc0b39d20 pid 0 lid 2 lowest kstack 0xc71b22c0
panic: trap
cpu0: Begin traceback...
vpanic(c04ecfa5,c71b4a60,c71b4ae4,c03d2d46,c04ecfa5,c71b4af0,c71b4af0,2,c71b22c0,10202) at netbsd:vpanic+0x11a
panic(c04ecfa5,c71b4af0,c71b4af0,2,c71b22c0,10202,e7acbfff,8,c05c99c0,100) at netbsd:panic+0x18
trap() at netbsd:trap+0xbe6
--- trap (number 6) ---
dodumpsys(c71b4cbc,8,100,c02aae3d,8,1104b14,0,c049e11c,c057c11c,c71b4ba4) at netbsd:dodumpsys+0x34d
dumpsys(100,0,c71b4c4c,c013ec40,0,0,0,c71b4bc8,8,0) at netbsd:dumpsys+0x14
db_sync_cmd(0,0,0,c71b4bc8,8,0,0,4857f550,a,d) at netbsd:db_sync_cmd+0x2e
...



>How-To-Repeat:
On a console of a i386 or amd64 DomU, break into ddb with +++++ and
issue a sync command.

>Fix:


>Audit-Trail:
From: Manuel Bouyer <bouyer@antioche.eu.org>
To: gnats-bugs@NetBSD.org
Cc: port-xen-maintainer@NetBSD.org, gnats-admin@NetBSD.org,
        netbsd-bugs@NetBSD.org
Subject: Re: port-xen/49869: Xen DomU fails to crash dump
Date: Sun, 3 May 2015 23:19:56 +0200

 On Sat, May 02, 2015 at 07:50:00AM +0000, mlelstv@serpens.de wrote:
 > >Description:
 > Neither a i386 nor a amd64 DomU are able to dump core after a system
 > panic.
 > 
 > amd64 provides an empty memory map (dumpsize = 0) to the dump functions.
 > These will then just abort with the message "not possible".
 > 
 > i386 panics when you try to run the 'sync' command in ddb.

 this is a known issue. From memory, the problem is with the pa -> ma
 translation. This may be fixable without too much work, but then there
 woukd be another problem:
 the MI dump functions (and also /dev/mem) uses PA addresses
 as offsets, but some pointers (including the page tables) uses MA
 addresses. This basically means that the dump would be unusable.
 This is not easy to fix and would require changes to the crash
 dump analysis tools.

 -- 
 Manuel Bouyer <bouyer@antioche.eu.org>
      NetBSD: 26 ans d'experience feront toujours la difference
 --

>Unformatted:

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