> -----Original Message----- > From: Wood Scott-B07421 > Sent: Thursday, May 17, 2012 3:37 AM > To: Sethi Varun-B16395 > Cc: Alexander Graf; Bhushan Bharat-R65777; kvm-ppc@xxxxxxxxxxxxxxx > Subject: Re: [PATCH] KVM: PPC: Not optimizing MSR_CE and MSR_DE with > paravirt. > > On 05/16/2012 10:13 AM, Sethi Varun-B16395 wrote: > >>> Why is MSR[CE] unsafe? > >> > >> MSR=0 > >> * critical interrupt comes in * > >> mtmsr(MSR_CE) > >> --> MSR == MSR_CE > >> * interrupt should be delivered, but host doesn't get notified that > >> MSR_CE is changing * > >> > >> However, we completely ignore critical interrupts in KVM these days, > no? > > Watchdog will use them. > > > Well, it's least likely that MSR_CE/MSR_ME would get changed directly. > > They would mostly get changed via rfci/rfmci, which would trap. > > It being unlikely means that there's little performance downside to this > patch -- it doesn't mean that this patch is unnecessary. > Agreed. > FWIW, Topaz directly manipulates MSR[CE] extensively, since it uses > critical interrupts as its main interrupts (to distinguish from EE > interrupts which are delivered directly to the guest). > Yes, but at least we won't see that happening with linux. -Varun -- To unsubscribe from this list: send the line "unsubscribe kvm-ppc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
