Data corruption in guest using KVM

[Aurelien Jarno <aurelien-rXXEIb44qovR7s880joybQ@public.gmane.org>]

Hi all,

For a long time I am seeing data corruption in guests when using KVM,
but I am convinced only since today that the problem comes from KVM.

The symptoms are a few bytes that are mangled to 0x00 in a file that has
been written. For now I have only seen 2 or 4 consecutive bytes mangled,
but that may due to statistics given the limited samples.

The problem appears very rarely. I am only seeing it when doing huge 
compilations (for example gcc or glibc), and not for every build. Note
that I am only detecting build failures, so I can miss some corruptions.

Note that I have observed the problem on GNU/Linux, GNU/kFreeBSD and
plain FreeBSD, for both 32 and 64-bit guests. I always used 64-bit 
hosts, and I have seen the problem on both Core 2 and Athlon 64 CPU
(always multi-core).

I have never seen such corruptions using QEMU, so I would say the
problem does not comes from the disk emulation, though it may be due to
statistics. Note that I have made a lot of compilation in a MIPS QEMU
guest (a few hundred of hours), without any problem. This platform uses
the same IDE controller as the one in KVM.

Does anybody have seen the same kind of problem? Without a way to 
reproduce the corruption, I think it will be very difficult to debug 
the problem.

Regards,
Aurelien

-- 
  .''`.  Aurelien Jarno	            | GPG: 1024D/F1BCDB73
 : :' :  Debian developer           | Electrical Engineer
 `. `'   aurel32-8fiUuRrzOP0dnm+yROfE0A@public.gmane.org         | aurelien-rXXEIb44qovR7s880joybQ@public.gmane.org
   `-    people.debian.org/~aurel32 | www.aurel32.net

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