[PATCH 0/1] Fixes for LP:#1494350

[Stefan Bader]

On 08.03.2016 14:38, liang.chen at canonical.com wrote:
> BugLink: http://bugs.launchpad.net/bugs/1494350

Will this not be submitted as a upstream stable patch? If not at least the bug
report should have a Linux (Ubuntu) and tasks for the releases, plus some
testing feedback with at least one release and that patch added. (imo)

-Stefan

> 
> [Impact]
> Steal time can get overflowed after loading/migrating of a VM, which causes
> some guest OS like Debian Jessie to extremely large values for steal time.
> 
> % cat /proc/stat
> cpu 2400 0 1842 650879168 2579640 0 25 136562317270 0 0
> cpu0 1366 0 1028 161392988 1238598 0 11 383803090749 0 0
> cpu1 294 0 240 162582008 639105 0 8 39686436048 0 0
> cpu2 406 0 338 163331066 383867 0 4 333994238765 0 0
> cpu3 332 0 235 163573105 318069 0 1 1223752959076 0 0
> 
> [Justification]
> It is very important for guest system to know the real steal time in
> virtualized environment. People heavily depend on this figure when analysing
> performance issues in guest system.
> 
> [Test Case]
> 1.launching a VM and take down the steal time, e.g. rdmsr 0x4b564d03 to read
>   the location of the steal_time structure in guest and xp /ug <location> in
>   qemu monitor to dump the steal_time value 
> 2.save the state of the VM in a snapshot (savevm)
> 3.put some stress on the host machine, e.g. stress -c XXX
> 4.load the state of the VM (loadvm)
> 5.Look at the steal time again, it will very likely go backwards because of
>   the overflow
> 
> Marcelo Tosatti (1):
>   KVM: x86: move steal time initialization to vcpu entry time
> 
>  arch/x86/kvm/x86.c | 9 ++-------
>  1 file changed, 2 insertions(+), 7 deletions(-)
> 


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