Public bug reported:
When using Ubuntu Lucid as a KVM guest and either
a) propagating the host CPU to the guest (-cpu host) on an AMD Opteron 61xx
processor (Magny-Cours) or
b) forcing the guest CPU to be a Magny-Cours (-cpu
qemu64,family=16,model=9,vendor=AuthenticAMD)
the guest kernel crashes early with a panic related to a division error:
--------------
[ 0.074409] CPU: L1 I Cache: 64K (64 bytes/line), D cache 64K (64 bytes/line)
[ 0.075503] CPU: L2 Cache: 512K (64 bytes/line)
[ 0.076227] divide error: 0000 [#1] SMP
[ 0.076870] last sysfs file:
[ 0.077332] CPU 0
[ 0.077673] Modules linked in:
[ 0.078169] Pid: 0, comm: swapper Not tainted 2.6.32-16-generic #25-Ubuntu
Bochs
[ 0.079284] RIP: 0010:[<ffffffff8154ec6a>] [<ffffffff8154ec6a>]
init_amd+0x29c/0x3bd
[ 0.080000] RSP: 0018:ffffffff817adea8 EFLAGS: 00010246
[ 0.080000] RAX: 0000000000000000 RBX: ffffffff8185b380 RCX: ffff880001c00000
[ 0.080000] RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
[ 0.080000] RBP: ffffffff817adef8 R08: 00000000ffffffff R09: 0000000000000001
[ 0.080000] R10: 0000000000000004 R11: 0000000000000000 R12: ffffffff8185b394
[ 0.080000] R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000013800
[ 0.080000] FS: 0000000000000000(0000) GS:ffff880001c00000(0000)
knlGS:0000000000000000
[ 0.080000] CS: 0010 DS: 0018 ES: 0018 CR0: 000000008005003b
[ 0.080000] CR2: 0000000000000000 CR3: 0000000001001000 CR4: 00000000000006b0
[ 0.080000] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 0.080000] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
[ 0.080000] Process swapper (pid: 0, threadinfo ffffffff817ac000, task
ffffffff817d4600)
[ 0.080000] Stack:
[ 0.080000] ffffffff817adfa8 0000000000013800 ffffffff817adef8
ffffffff8154e1d9
[ 0.080000] <0> 80802001078bfbfd 00100f9100000800 ffffffff8185b380
0000000000000000
[ 0.080000] <0> ffffffff81973000 ffffffff817adfa8 ffffffff817adf18
ffffffff8154e2d4
[ 0.080000] Call Trace:
[ 0.080000] [<ffffffff8154e1d9>] ? generic_identify+0x12e/0x13e
[ 0.080000] [<ffffffff8154e2d4>] identify_cpu+0xeb/0x1db
[ 0.080000] [<ffffffff8188280f>] identify_boot_cpu+0x10/0x3e
[ 0.080000] [<ffffffff818828a6>] check_bugs+0x9/0x2d
[ 0.080000] [<ffffffff8187add1>] start_kernel+0x348/0x365
[ 0.080000] [<ffffffff8187a33a>] x86_64_start_reservations+0x125/0x129
[ 0.080000] [<ffffffff8187a438>] x86_64_start_kernel+0xfa/0x109
[ 0.080000] Code: 8b b3 b2 00 00 00 4d 63 f6 0f b6 d2 4a 8b 0c f5 00 b7 85 81
48 c7 c0 f4 e3 00 00 8d 14 72 66 89 14 08 0f b7 83 b4 00 00 00 31 d2 <41> f7 f5
66 89 93 b4 00 00 00 48 89 df e8 13 fc ff ff 81 7b 0c
[ 0.080000] RIP [<ffffffff8154ec6a>] init_amd+0x29c/0x3bd
[ 0.080000] RSP <ffffffff817adea8>
[ 0.080017] ---[ end trace a7919e7f17c0a725 ]---
This is caused by an unchecked PCI config space access in
arch/x86/kernel/cpu/amd.c:amd_fixup_dcm(), which is only called when a family
10h model 9 processor (aka Magny-Cours) is detected. Since KVM does not provide
an emulation of the AMD Northbridge PCI device, the resulting values are bogus
and trigger a division by zero error. The upstream patch:
commit 9d260ebc09a0ad6b5c73e17676df42c7bc75ff64
Author: Andreas Herrmann <herrmann.der.u...@googlemail.com>
Date: Wed Dec 16 15:43:55 2009 +0100
removes this PCI access and replaces it with the more virtualization friendly
MSR access to get the same information.
-cpu host will become the new default for KVM, so please seriously consider
back-porting this patch (which simplifies the code) and is upstream since
2.6.33-rc1
If not back-ported, KVM guests with Ubuntu Lucid will not run on AMD
Magny-Cours machines in the future.
** Affects: linux (Ubuntu)
Importance: Undecided
Status: New
--
kernel crash under KVM when on AMD Magny-Cours
https://bugs.launchpad.net/bugs/556480
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