On 10.01.2012, at 01:51, Scott Wood wrote:

On 01/09/2012 11:46 AM, Alexander Graf wrote:

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On 21.12.2011, at 02:34, Scott Wood wrote:

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Current issues include:
- Machine checks from guest state are not routed to the host handler.
- The guest can cause a host oops by executing an emulated instruction
 in a page that lacks read permission.  Existing e500/4xx support has
 the same problem.

We solve that in book3s pr by doing

 LAST_INST = <known bad value>;
 PACA->kvm_mode = <recover at next inst>;
 lwz(guest pc);
 do_more_stuff();

That way when an exception occurs at lwz() the DO_KVM handler checks that we're in kvm mode "recover" which does basically srr0+=4; rfi;.

I was thinking we'd check ESR[EPID] or SRR1[IS] as appropriate, and
treat it as a kernel fault (search exception table) -- but this works
too and is a bit cleaner (could be other uses of external pid), at the
expense of a couple extra instructions in the emulation path (but
probably a slightly faster host TLB handler).

The check wouldn't go in DO_KVM, though, since on bookehv that only
deals with diverting flow when xSRR1[GS] is set, which wouldn't be the
case here.

Thinking about it a bit more, how is this different from a failed get_user()? We can just use the same fixup mechanism as there, right?

Alex