Re: [PATCH -v2] Monitor command: pfa2hva, translate guest physical address to host virtual address

[Huang Ying <ying.huang@intel.com>]

On Wed, 2010-11-10 at 16:28 +0800, Avi Kivity wrote:
> On 11/10/2010 09:41 AM, Huang Ying wrote:
> > On Wed, 2010-11-10 at 14:59 +0800, Avi Kivity wrote:
> > >  On 11/10/2010 08:56 AM, Avi Kivity wrote:
> > >  >  On 11/08/2010 05:39 AM, Anthony Liguori wrote:
> > >  >>>  Yes. The main usage of the interface is automated testing.
> > >  >>
> > >  >>  That's precisely what the command should not be used for.
> > >  >>
> > >  >>  You can't assume a gpa ->  hva mapping is consistent in an external
> > >  >>  application.  If you want to implement an interface for testing, you
> > >  >>  have to push more of the logic into QEMU to avoid the race.
> > >  >
> > >  >  An alternative is to use -mempath.  Does poisoning work for tmpfs?
> > >  >
> > >  Or hugetlbfs - I think it does?
> >
> > The QEMU support for hugetlbfs has some issues now. Because it is hard
> > for QEMU to deal with 2M poisoned page reported by host OS. Although it
> > is possible for QEMU to relay 2M poisoned page as MCE to guest OS, the
> > guest OS may not work properly for this kind of MCE.
> >
> 
> If we get a full address (rather than just a frame number) then we can 
> identify the 4k page and send an mce just for that frame?

We need host kernel to break down the 2M huge page into 4k pages. Then
send SIGBUS to QEMU with the poisoned 4k page. Because host kernel will
poison the whole 2M virtual address space otherwise, and other 4k pages
inside the 2M page can not used accessed in guest (will trigger SIGBUS
and SRAR MCE).

Best Regards,
Huang Ying