Re: [PATCH 14/23] KVM: PPC: Book3S PR: Delay disabling relocation-on interrupts

[Paul Mackerras <paulus@samba.org>]

On Fri, Aug 30, 2013 at 06:30:50PM +0200, Alexander Graf wrote:
> 
> On 06.08.2013, at 06:23, Paul Mackerras wrote:
> 
> > When we are running a PR KVM guest on POWER8, we have to disable the
> > new POWER8 feature of taking interrupts with relocation on, that is,
> > of taking interrupts without disabling the MMU, because the SLB does
> > not contain the normal kernel SLB entries while in the guest.
> > Currently we disable relocation-on interrupts when a PR guest is
> > created, and leave it disabled until there are no more PR guests in
> > existence.
> > 
> > This defers the disabling of relocation-on interrupts until the first
> 
> It would've been nice to see the original patch on kvm-ppc@vger.

Here are the headers from my copy of the original mail:

> Date: Tue, 6 Aug 2013 14:23:37 +1000
> From: Paul Mackerras <paulus@samba.org>
> To: Alexander Graf <agraf@suse.de>, Benjamin Herrenschmidt <benh@kernel.crashing.org>
> Cc: kvm-ppc@vger.kernel.org, kvm@vger.kernel.org
> Subject: [PATCH 14/23] KVM: PPC: Book3S PR: Delay disabling relocation-on interrupts

So as far as I can see, I *did* cc it to kvm-ppc@vger.

> > +	if (!kvm->arch.relon_disabled) {
> > +		if (firmware_has_feature(FW_FEATURE_SET_MODE)) {
> 
> Is this the same as the endianness setting rtas call? If so, would a PR guest in an HV guest that provides only endianness setting but no relocation-on setting confuse any of this code?

It is the same hcall, but since the interrupts-with-relocation-on
function was defined in the first PAPR version that has H_SET_MODE,
we shouldn't ever hit that situation.  In any case, if we did happen
to run under a (non PAPR-compliant) hypervisor that implemented
H_SET_MODE but not the relocation-on setting, then we couldn't have
enabled relocation-on interrupts in the first place, so it wouldn't
matter.

Paul.