Patch for MS Hyper V (virtualization)

John Baldwin jhb at
Mon Apr 6 09:10:27 PDT 2009

On Sunday 05 April 2009 12:23:39 pm Sergey Babkin wrote:
>    Apr 4, 2009 02:10:23 PM, ivoras at wrote:
>    >Can someo=ne please review and commit (if appropriate) the tweak for
>    >Hyper-V shu=tdown issue at
>    >?
>    >
>    =>>The problem is: the VM appears to hang on shutdown without it
>    (hanging
>    >the Hyper-V VM with it so the host also can't shutdown or reboot
>    >re=liably - someone at MS skipped the part where an error in the VM
>    >isn't=supposed to bring the host down with it)
>    I don't have the commit =permission any more but I can review :-)
>    Yes, Hyper-V does not like th=e writes into the PCI config space.
>    Very specifically,
>    writing the base=register window address of the simulated 21140
>    screws up something
>    tha=t prevents the VM from shutting down. Interestingly, even reading
>    and writi=ng
>    back the same value has this effect. So the patch is valid.
>    =>I don't particularly like the hackish checking for the 21140 chip,
>    and I'=m not sure
>    if if would break some real 21140 chip out there. If the dri=ver does
>    the same as another
>    one I've seen, the driver tries to align t=he register window to
>    0x80, and in the
>    simulated 21140 it's already ali=gned. I've had a quick look but
>    couldn't say it
>    for sure. I'd do it dif=ferently: check if the value being written is
>    the same that was read,
>    =and skip the write in this case.
>    Let me see, maybe I'll make a dif=ferent patch.

Hmm, the problem is we need to be able to write to BARs to size them.  Any OS 
needs to be able to do this to know what address space regions are being 
decoded by devices.  We can't avoid writing to BARs.

John Baldwin

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