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

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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[...]

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Current issues include:
- Machine checks from guest state are not routed to the host =

handler.

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- The guest can cause a host oops by executing an emulated =

instruction

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 in a page that lacks read permission.  Existing e500/4xx support =

has

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 the same problem.

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We solve that in book3s pr by doing
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 LAST_INST =3D <known bad value>;
 PACA->kvm_mode =3D <recover at next inst>;
 lwz(guest pc);
 do_more_stuff();
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That way when an exception occurs at lwz() the DO_KVM handler checks =

that we're in kvm mode "recover" which does basically srr0+=3D4; rfi;.

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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).
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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