Re: [Qemu-devel] race between kvm-kmod-3.0 and kvm-kmod-3.3 // was: race condition in qemu-kvm-1.0.1

[Peter Lieven <pl@dlhnet.de>]

On 02.07.2012 17:05, Avi Kivity wrote:
> On 06/28/2012 12:38 PM, Peter Lieven wrote:
>> does anyone know whats that here in handle_mmio?
>>
>>      /* hack: Red Hat 7.1 generates these weird accesses. */
>>      if ((addr>  0xa0000-4&&  addr<= 0xa0000)&&  kvm_run->mmio.len == 3)
>>          return 0;
>>
> Just what it says.  There is a 4-byte access to address 0x9ffff.  The
> first byte lies in RAM, the next three bytes are in mmio.  qemu is
> geared to power-of-two accesses even though x86 can generate accesses to
> any number of bytes between 1 and 8.
I just stumbled across the word "hack" in the comment. When the race
occurs the CPU is basically reading from 0xa0000 in an endless loop.
> It appears that this has happened with your guest.  It's not impossible
> that it's genuine.
>
I had a lot to do the last days, but I update our build environment to
Ubuntu LTS 12.04 64-bit Server which is based on Linux 3.2.0. I still
see the issue. If I use the kvm Module provided with the kernel it is
working correctly. If I use kvm-kmod-3.4 with qemu-kvm-1.0.1 (both
from sourceforge) I can reproduce the race condition.

I will keep you posted when I have more evidence.

Thanks,
Peter