Re: [Bug 104091] New: [bisected] Starting a VM causes the host to halt and create Machine Check Exceptions

Xiao Guangrong <guangrong.xiao@xxxxxxxxxxxxxxx> · Sun, 6 Sep 2015 18:28:38 +0800

On 09/06/2015 06:03 PM, bugzilla-daemon@xxxxxxxxxxxxxxxxxxx wrote:
https://bugzilla.kernel.org/show_bug.cgi?id=104091

             Bug ID: 104091
            Summary: [bisected] Starting a VM causes the host to halt and
                     create Machine Check Exceptions
            Product: Virtualization
            Version: unspecified
     Kernel Version: 4.2
           Hardware: All
                 OS: Linux
               Tree: Mainline
             Status: NEW
           Severity: normal
           Priority: P1
          Component: kvm
           Assignee: virtualization_kvm@xxxxxxxxxxxxxxxxxxxx
           Reporter: harn-solo@xxxxxx
         Regression: No

Created attachment 186851
   --> https://bugzilla.kernel.org/attachment.cgi?id=186851&action=edit
dmesg output after starting the VM

With kernel 4.2, starting one of my VMs instantly freezes the host system and
creates Machine Check Exceptions on CPUs dedicated to that particula VM:

[12316.171917] mce: [Hardware Error]: CPU 3: Machine Check Exception: 5 Bank
17: be2000000003110a
[12316.171917] mce: [Hardware Error]: RIP !INEXACT! 10:<ffffffff813217fd>
{intel_idle+0xbd/0x120}
[12316.171917] mce: [Hardware Error]: TSC 76fd7352bf6 ADDR fa137140 MISC
30f0083884509086
[12316.171917] mce: [Hardware Error]: PROCESSOR 0:306f2 TIME 1441130705 SOCKET
0 APIC 6 microcode 2d
[12316.171917] mce: [Hardware Error]: Run the above through 'mcelog --ascii'
...

Could you please decode it by mcelog?

A bisection revealed that commit fd717f11015f673487ffc826e59b2bad69d20fe5
introduced the problem:

KVM: x86: apply guest MTRR virtualization on host reserved pages

Currently guest MTRR is avoided if kvm_is_reserved_pfn returns true.
However, the guest could prefer a different page type than UC for
such pages. A good example is that pass-throughed VGA frame buffer is
not always UC as host expected.

This patch enables full use of virtual guest MTRRs.

One could argue that the following warning is an obvious hint
[12311.584431] pmd_set_huge: Cannot satisfy [mem 0x383fe0000000-0x383fe0200000]
with a huge-page mapping due to MTRR override.

Just confirm: it happened on host, right?

but I'm able to run another VM without problems despite that warning.

Please let me know I you need additional information.

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