Re: [RFC][KVM][PATCH 1/1] kvm:ppc:booke-64: soft-disable interrupts

From: Scott Wood <scottwood@freescale.com>
To: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Wood Scott-B07421 <B07421@freescale.com>,
	"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
	Caraman Mihai Claudiu-B02008 <B02008@freescale.com>,
	"agraf@suse.de" <agraf@suse.de>,
	"kvm-ppc@vger.kernel.org" <kvm-ppc@vger.kernel.org>,
	"tiejun.chen" <tiejun.chen@windriver.com>,
	Bhushan Bharat-R65777 <R65777@freescale.com>,
	"linuxppc-dev@lists.ozlabs.org" <linuxppc-dev@lists.ozlabs.org>
Subject: Re: [RFC][KVM][PATCH 1/1] kvm:ppc:booke-64: soft-disable interrupts
Date: Thu, 9 May 2013 16:27:36 -0500	[thread overview]
Message-ID: <1368134856.654.11@snotra> (raw)
In-Reply-To: <1368103062.25488.193.camel@pasglop> (from benh@kernel.crashing.org on Thu May  9 07:37:42 2013)

On 05/09/2013 07:37:42 AM, Benjamin Herrenschmidt wrote:
> On Thu, 2013-05-09 at 17:44 +0800, tiejun.chen wrote:
> >
> > Actually in the case GS=1 even if EE=0, EXT/DEC/DBELL still occur  
> as I
> > recall.
> 
> Only if directed to the hypervisor.

This is always the case with KVM, right?  At least on booke...

> > > Case 1)
> > >   -> Local_irq_disable()  will set soft_enabled = 0
> > >   -> Now Externel interrupt happens, there we set PACA_IRQ_EE in
> > irq_happened, Also clears EE in SRR1 and rfi. So interrupts are hard
> > disabled. No more other interrupt gated by MSR.EE can happen. Looks
> > like the idea here is to not let a device keep on inserting  
> interrupt
> > till the interrupt condition on device is cleared, right?
> 
> The external interrupt line is level sensitive normally, so we have to
> mask MSR:EE in that case or the interrupt would keep re-occurring  
> (note
> that FSL has this concept of auto-acked interrupts via the on die MPIC
> for which you can potentially use PACA_IRQ_EE_EDGE instead and avoid
> having to mask MSR:EE).

Note that if we do this, we can no longer leave the interrupt vector in  
EPR, and would have to track (potentially multiple different) pending  
external interrupts in software.

-Scott