Re: Data corruption in guest using KVM

[Avi Kivity <avi-atKUWr5tajBWk0Htik3J/w@public.gmane.org>]

Aurelien Jarno wrote:
> 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.

Did you observe anything about the corruption?  For example, are the 
offsets at page boundary?  Can you provide a corrupted file and the 
same, non-corrupted file as a reference?

For the 32-bit case, were the guests pae, nonpae, or both?

How would I go about reproducing this?   Is a single ./configure; make 
clean; make in a loop compiling gcc sufficient?

-- 
error compiling committee.c: too many arguments to function


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