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

[Avi Kivity <avi@redhat.com>]

On 11/12/2010 03:16 AM, Huang Ying wrote:
> On Thu, 2010-11-11 at 17:39 +0800, Avi Kivity wrote:
> >  On 11/11/2010 02:56 AM, Huang Ying wrote:
> >  >  On Thu, 2010-11-11 at 00:49 +0800, Anthony Liguori wrote:
> >  >  >   On 11/10/2010 02:34 AM, Avi Kivity wrote:
> >  >  >   >>   Why the gpa ->    hva mapping is not
> >  >  >   >>   consistent for RAM if -mempath is not used?
> >  >  >   >
> >  >  >   >   Video RAM in the range a0000-bffff and PCI mapped RAM can change gpas
> >  >  >   >   (while remaining in the same hva).
> >  >  >   >
> >  >  >   >   Even for ordinary RAM, which doesn't normally change gpa/hva, I'm not
> >  >  >   >   sure we want to guarantee that it won't.
> >  >  >
> >  >  >   We can't universally either.  Memory hot remove potentially breaks the
> >  >  >   mapping and some non-x86 architectures (like ARM) can alias RAM via a
> >  >  >   guest triggered mechanism.
> >  >
> >  >  Thanks for clarification. Now I think we have two options.
> >  >
> >  >  1) Clearly mark gpa2hva (pfa2hva now, should renamed to gpa2hva) as a
> >  >  testing only interface, and should be used only on restricted
> >  >  environment (normal memory, without hot-remove, maybe only on x86).
> >  >
> >  >  2) Find some way to lock the gpa ->   hva mapping during operating. Such
> >  >  as gpa2hva_begin and gpa2hva_end and lock the mapping in between.
> >  >
> >  >  I think 2) may be possible. But if there are no other users, why do that
> >  >  for a test case? So I think 1) may be the better option.
> >  >
> >
> >  3) Move the poisoning code into qemu, so the command becomes
> >
> >      posison-address<addr>
> >
> >  (though physical addresses aren't stable either)
>
> Poisoning includes:
>
> a) gva ->  gpa
> b) gpa ->  hva
> c) hva ->  hpa
> d) inject the MCE into host via some external tool
>
> poison-address need to do b, c, d. Do you think it is good to do all
> these inside qemu?

If d is not too complicated (an ioctl?), we might to it in qemu.

> >  4) Use -mempath on /dev/shm and poison a page in the backing file
>
> If we can poison a page in the backing file, how do we know the
> corresponding gpa and hpa?

I think you currently can't know it's gpa (why do you want to?); the 
upcoming NUMA enhancements should allow this (the plan is to have a file 
per guest NUMA node, so we can tell the host what policy to apply for 
that node).

gpa->hpa translation can be derived from /proc/pid/maps.

-- 
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