Re: [PATCH 3/3] Fix TSC MSR read in nested SVM

Nadav Har'El
2011-08-10T12:35:36Z

On Sun, Aug 07, 2011, Joerg Roedel wrote about "Re: [PATCH 3/3] Fix TSC MSR read in nested SVM":
> > Joerg, can you review and ack Nadav's SVM patch? TIA
>
> Tested-by: Joerg Roedel <joerg.roedel@amd.com>
> Acked-by: Joerg Roedel <joerg.roedel@amd.com>
>
> Reviewed and tested (didn't apply cleanly, but was easy to fix that up).
> Looks all good so far.

Hi guys, I'm a bit confused how we want to proceed from here.

The patches which I sent appear to fix the original bug (as confirmed by
the two people who reported it), but Zachary warned that it would break
migration of nested SVM while L2 is running. I asked whether migration
works at all while L2 is running (without exiting to L1 first) - and
Marcelo suggested that it doesn't.

If the problem Zachary pointed to is considered serious, I proposed a second
option - to leave the code to *wrongly* return the L1 TSC MSR always, and
check (and warn) in situations where this value is wrongly returned to the
guest, but this will leave qemu to always read the TSC MSR from L1, even when
L2 is running. While I proposed this as a second option, I don't think I
can recommend it.

So what's the verdict? :-)

Thanks,
Nadav.

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