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

2015-09-06 Thread bugzilla-daemon 
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_...@kernel-bugs.osdl.org
  Reporter: harn-s...@gmx.de
Regression: No

Created attachment 186851
  --> https://bugzilla.kernel.org/attachment.cgi?id=186851=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: be23110a
[12316.171917] mce: [Hardware Error]: RIP !INEXACT! 10:
{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'
...

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 0x383fe000-0x383fe020]
with a huge-page mapping due to MTRR override.

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

2015-09-06 Thread Xiao Guangrong 



On 09/06/2015 06:03 PM, bugzilla-dae...@bugzilla.kernel.org 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_...@kernel-bugs.osdl.org
   Reporter: harn-s...@gmx.de
 Regression: No

Created attachment 186851
   --> https://bugzilla.kernel.org/attachment.cgi?id=186851=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: be23110a
[12316.171917] mce: [Hardware Error]: RIP !INEXACT! 10:
{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 0x383fe000-0x383fe020]
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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