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From: Alexander Graf <agraf@suse.de>
Subject: Re: [RFC PATCH 14/16] KVM: PPC: booke: category E.HV (GS-mode) support
Date: Thu, 12 Jan 2012 08:11:11 +0100
To: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Scott Wood <scottwood@freescale.com>,
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 "kvm-ppc@vger.kernel.org" <kvm-ppc@vger.kernel.org>,
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On 12.01.2012, at 07:44, Benjamin Herrenschmidt <benh@kernel.crashing.org> w=
rote:

> On Tue, 2012-01-10 at 04:11 +0100, Alexander Graf wrote:
>> This is what book3s does:
>>=20
>>                case EMULATE_FAIL:
>>                        printk(KERN_CRIT "%s: emulation at %lx failed
>> (%08x)\n",
>>                               __func__, kvmppc_get_pc(vcpu),
>> kvmppc_get_last_inst(vcpu));
>>                        kvmppc_core_queue_program(vcpu, flags);
>>                        r =3D RESUME_GUEST;
>>=20
>> which also doesn't throttle the printk, but I think injecting a
>> program fault into the guest is the most sensible thing to do if we
>> don't know what the instruction is supposed to do. Best case we get an
>> oops inside the guest telling us what broke :).
>=20
> You can also fallback to a slow path that reads the guest TLB,
> translates then reads the instruction. Of course you have to be careful
> as such a manual translate + read + execute needs to be somewhat
> synchronized with a possible TLB invalidation :-)

Well we do want to be fast on the default path though. So yes, what you're s=
aying is what book3s does, but as a fallback in case the fast path didn't wo=
rk.

The problem here however is that we don't know if the fast path failed; we o=
ops.


>=20
> (MMIO emulation is broken in this regard too btw)

Huh?

Alex

>=20
> Cheers,
> Ben.
>=20
>=20