Re: [RFC PATCH v3 5/6] kvm/ppc/mpic: in-kernel MPIC emulation

Alexander Graf
2013-04-04T09:42:20Z

On 04.04.2013, at 00:54, Scott Wood wrote:

> On 04/03/2013 05:12:06 PM, Alexander Graf wrote:
>> Am 04.04.2013 um 00:07 schrieb Scott Wood <scottwood@freescale.com>:
>> > On 04/03/2013 04:58:56 PM, Alexander Graf wrote:
>> >> Am 03.04.2013 um 23:38 schrieb Scott Wood <scottwood@freescale.com>:
>> >> > On 04/03/2013 11:19:42 AM, Alexander Graf wrote:
>> >> >> On 03.04.2013, at 03:57, Scott Wood wrote:
>> >> >> > Hook the MPIC code up to the KVM interfaces, add locking, etc.
>> >> >> >
>> >> >> > TODO: irqfd support, split up into multiple patches, KVM_IRQ_LINE
>> >> >> > support
>> >> >> >
>> >> >> > Signed-off-by: Scott Wood <scottwood@freescale.com>
>> >> >> > ---
>> >> >> > v3: mpic_put -> kvmppc_mpic_put
>> >> >> >
>> >> >> >
>> >> >> [...]
>> >> >> > +void kvmppc_mpic_set_epr(struct kvm_vcpu *vcpu);
>> >> >> > +
>> >> >> > int kvm_vcpu_ioctl_config_tlb(struct kvm_vcpu *vcpu,
>> >> >> > struct kvm_config_tlb *cfg);
>> >> >> > int kvm_vcpu_ioctl_dirty_tlb(struct kvm_vcpu *vcpu,
>> >> >> > diff --git a/arch/powerpc/kvm/Kconfig b/arch/powerpc/kvm/Kconfig
>> >> >> > index 63c67ec..a87139b 100644
>> >> >> > --- a/arch/powerpc/kvm/Kconfig
>> >> >> > +++ b/arch/powerpc/kvm/Kconfig
>> >> >> > @@ -151,6 +151,11 @@ config KVM_E500MC
>> >> >> >
>> >> >> > If unsure, say N.
>> >> >> >
>> >> >> > +config KVM_MPIC
>> >> >> > + bool "KVM in-kernel MPIC emulation"
>> >> >> > + depends on KVM
>> >> >> This should probably depend on FSL KVM for now, until someone adds support for other MPIC revisions.
>> >> >
>> >> > I don't see a symbol specifically for "FSL KVM". What part of the MPIC code depends on booke or any FSL-specific code?
>> >> You support only FSL mpic device IDs :). So if someone on book3s goes along and sees this, he'd think "yes, I want an in-kernel MPIC", enables the option and wastes space.
>> >
>> > "Would this waste space" is not generally the criteria for kconfig dependencies. Who is the kernel to get in the way of someone that wants an FSL MPIC on a 4xx VM? :-)
>> >
>> > And again, there's no symbol for FSL KVM -- I'd have to use a list that could get out of date. And it would reduce build testing in allyesconfig-type configs.
>> Ok, please indicate compatibility limitations in the Kconfig description at least then.
>
> OK -- not really a "compatibility" limitation so much as what models are supported.
>
> Note that mpc86xx has a 74xx-derived core, but also has an FSL MPIC...
>
> Is 74xx/e600 supported by book3s_pr? Can't tell from the kconfig text. :-)

On book3s_pr we don't have a good compatibility check mechanism in place. That's really suboptimal.

What I'm saying is that Kconfig should say "In-kernel emulation of FSL MPIC 2.0 and FSL MPIC 4.2 interrupt controllers. Say Y here if you plan to run KVM on an FSL system". That'd be in line with what you can actually enable using the ioctls and leaves the decision whether that's a good thing to the user.

Code-wise there shouldn't be any dependency on host or guest architecture of course.

Alex