[RFC PATCH 14/16] KVM: PPC: booke: category E.HV (GS-mode) support

[Alexander Graf]

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

> On 01/09/2012 11:46 AM, Alexander Graf wrote:
>> 
>> On 21.12.2011, at 02:34, Scott Wood wrote:
> 

[...]

>>> 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