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    SubjectRe: MCE boot crash in qemu
    On Mon, Jun 15, 2009 at 01:59:04PM +0200, Vegard Nossum wrote:
    > Hi,
    >
    > I get an MCE-related crash like this in latest linus tree:
    >
    > [ 0.115341] CPU: L1 I Cache: 64K (64 bytes/line), D cache 64K (64 bytes/line)
    > [ 0.116396] CPU: L2 Cache: 512K (64 bytes/line)
    > [ 0.120570] mce: CPU supports 0 MCE banks
    > [ 0.124870] BUG: unable to handle kernel NULL pointer dereference at 00000000
    > 00000010
    > [ 0.128001] IP: [<ffffffff813b98ad>] mcheck_init+0x278/0x320
    > [ 0.128001] PGD 0
    > [ 0.128001] Thread overran stack, or stack corrupted
    > [ 0.128001] Oops: 0002 [#1] PREEMPT SMP
    > [ 0.128001] last sysfs file:
    > [ 0.128001] CPU 0
    > [ 0.128001] Modules linked in:
    > [ 0.128001] Pid: 0, comm: swapper Not tainted 2.6.30 #426
    > [ 0.128001] RIP: 0010:[<ffffffff813b98ad>] [<ffffffff813b98ad>] mcheck_init+
    > 0x278/0x320
    > [ 0.128001] RSP: 0018:ffffffff81595e38 EFLAGS: 00000246
    > [ 0.128001] RAX: 0000000000000010 RBX: ffffffff8158f900 RCX: 0000000000000000
    > [ 0.128001] RDX: 0000000000000000 RSI: 00000000000000ff RDI: 0000000000000010
    > [ 0.128001] RBP: ffffffff81595e68 R08: 0000000000000001 R09: 0000000000000000
    > [ 0.128001] R10: 0000000000000010 R11: 0000000000000000 R12: 0000000000000000
    > [ 0.128001] R13: 00000000ffffffff R14: 0000000000000000 R15: 0000000000000000
    > [ 0.128001] FS: 0000000000000000(0000) GS:ffff880002288000(0000) knlGS:00000
    > 00000000000
    > [ 0.128001] CS: 0010 DS: 0018 ES: 0018 CR0: 000000008005003b
    > [ 0.128001] CR2: 0000000000000010 CR3: 0000000001001000 CR4: 00000000000006b0
    > [ 0.128001] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
    > [ 0.128001] DR3: 0000000000000000 DR6: 0000000000000000 DR7: 0000000000000000
    > [ 0.128001] Process swapper (pid: 0, threadinfo ffffffff81594000, task ffffff
    > ff8152a4a0)
    > [ 0.128001] Stack:
    > [ 0.128001] 0000000081595e68 5aa50ed3b4ddbe6e ffffffff8158f900 ffffffff8158f
    > 914
    > [ 0.128001] ffffffff8158f948 0000000000000000 ffffffff81595eb8 ffffffff813b8
    > 69c
    > [ 0.128001] 5aa50ed3b4ddbe6e 00000001078bfbfd 0000062300000800 5aa50ed3b4ddb
    > e6e
    > [ 0.128001] Call Trace:
    > [ 0.128001] [<ffffffff813b869c>] identify_cpu+0x331/0x392
    > [ 0.128001] [<ffffffff815a1445>] identify_boot_cpu+0x23/0x6e
    > [ 0.128001] [<ffffffff815a14ac>] check_bugs+0x1c/0x60
    > [ 0.128001] [<ffffffff8159c075>] start_kernel+0x403/0x46e
    > [ 0.128001] [<ffffffff8159b2ac>] x86_64_start_reservations+0xac/0xd5
    > [ 0.128001] [<ffffffff8159b3ea>] x86_64_start_kernel+0x115/0x14b
    > [ 0.128001] [<ffffffff8159b140>] ? early_idt_handler+0x0/0x71
    > [ 0.128001] Code: c7 48 89 05 9e 71 40 00 74 2a 48 63 15 91 71 40 00 be ff 00
    > 00 00 48 c1 e2 03 e8 bf a1 e2 ff e9 3f fe ff ff 48 8b 05 7b 71 40 00 <48> c7 00
    > 00 00 00 00 eb 84 c7 05 40 71 40 00 01 00 00 00 e9 2b
    > [ 0.128001] RIP [<ffffffff813b98ad>] mcheck_init+0x278/0x320
    > [ 0.128001] RSP <ffffffff81595e38>
    > [ 0.128001] CR2: 0000000000000010
    > [ 0.129306] ---[ end trace a7919e7f17c0a725 ]---
    >
    > It's this:
    >
    > /*
    > * Various K7s with broken bank 0 around. Always disable
    > * by default.
    > */
    > if (c->x86 == 6)
    > bank[0] = 0;
    >
    > in mce_cpu_quirks() in arch/x86/kernel/cpu/mcheck/mce.c around line
    > 1217. Strange that it thinks this is AMD cpu, though?

    Probably qemu fakes that. You can check in /proc/cpuinfo after
    it booted.

    It should really clear the mca cpuid flag if it doesn't have any mca banks,
    but ok.

    Here's a untested patch (sorry not able to test any patches currently).
    Does it fix the problem?

    A workaround if you don't want to apply the patch is to boot with mce=off

    -Andi

    ---

    x86: mce: Handle banks == 0 case in K7 quirk

    This happens on QEMU which reports MCA capability, but no banks.
    Without this patch there is a buffer overrun and boot ops because the code
    would try to initialize the 0 element of a zero length kmalloc()
    buffer.

    Signed-off-by: Andi Kleen <ak@linux.intel.com>

    --- linux-2.6.30-git8/arch/x86/kernel/cpu/mcheck/mce.c-o 2009-06-15 14:45:52.000000000 +0200
    +++ linux-2.6.30-git8/arch/x86/kernel/cpu/mcheck/mce.c 2009-06-15 14:46:40.000000000 +0200
    @@ -1245,7 +1245,7 @@
    * Various K7s with broken bank 0 around. Always disable
    * by default.
    */
    - if (c->x86 == 6)
    + if (c->x86 == 6 && banks > 0)
    bank[0] = 0;
    }




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