Re: [Qemu-devel] [PATCH v3 0/4] target-ppc: Add FWNMI support in qemu for powerKVM guests

[David Gibson]

On Wed, Nov 19, 2014 at 11:32:56AM +0100, Alexander Graf wrote:
> 
> 
> 
> > Am 19.11.2014 um 06:48 schrieb Aravinda Prasad <address@hidden>:
> > 
> > 
> > 
> > On Tuesday 11 November 2014 08:54 AM, David Gibson wrote:
> > 
> > [..]
> > 
> >> 
> >> So, this may not still be possible depending on whether the KVM side
> >> of this is already merged, but it occurs to me that there's a simpler
> >> way.
> >> 
> >> Rather than mucking about with having to update the hypervisor on the
> >> RTAS location, they have qemu copy the code out of RTAS, patch it and
> >> copy it back into the vector, you could instead do this:
> >> 
> >>  1. Make KVM instead of immediately delivering a 0x200 for a guest
> >> machine check, cause a special exit to qemu.
> >> 
> >>  2. Have the register-nmi RTAS call store the guest side MC handler
> >> address in the spapr structure, but perform no actual guest code
> >> patching.
> >> 
> >>  3. Allocate the error log buffer independently from the RTAS blob,
> >> so qemu always knows where it is.
> >> 
> >>  4. When qemu gets the MC exit condition, instead of going via a
> >> patched 0x200 vector, just directly set the guest register state and
> >> jump straight into the guest side MC handler.
> > 
> > Before I proceed further I would like to know what others think about
> > the approach proposed above (except for step 3 - as per PAPR the error
> > log buffer should be part of RTAS blob and hence we cannot have error
> > log buffer independent of RTAS blob).
> > 
> > Alex, Alexey, Ben: Any thoughts?
> 
> If in doubt, stick to PAPR please.

Apart from (3), which was a misunderstanding on my part, this doesn't
diverge from PAPR - it's just a question of how we're implementing the
PAPR behaviour.

-- 
David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!
http://www.ozlabs.org/~dgibson

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