> -----Original Message----- > From: Wood Scott-B07421 > Sent: Tuesday, April 02, 2013 11:30 PM > To: Bhushan Bharat-R65777 > Cc: Alexander Graf; kvm-ppc@xxxxxxxxxxxxxxx; kvm@xxxxxxxxxxxxxxx; Wood Scott- > B07421 > Subject: Re: [PATCH 4/4 v2] KVM: PPC: Add userspace debug stub support > > On 04/02/2013 09:09:34 AM, Bhushan Bharat-R65777 wrote: > > > > > > > -----Original Message----- > > > From: Alexander Graf [mailto:agraf@xxxxxxx] > > > Sent: Tuesday, April 02, 2013 1:57 PM > > > To: Bhushan Bharat-R65777 > > > Cc: kvm-ppc@xxxxxxxxxxxxxxx; kvm@xxxxxxxxxxxxxxx; Wood Scott-B07421 > > > Subject: Re: [PATCH 4/4 v2] KVM: PPC: Add userspace debug stub > > support > > > > > > > > > On 29.03.2013, at 07:04, Bhushan Bharat-R65777 wrote: > > > > > > > > > > > > > > >> -----Original Message----- > > > >> From: Alexander Graf [mailto:agraf@xxxxxxx] > > > >> Sent: Thursday, March 28, 2013 10:06 PM > > > >> To: Bhushan Bharat-R65777 > > > >> Cc: kvm-ppc@xxxxxxxxxxxxxxx; kvm@xxxxxxxxxxxxxxx; Wood > > Scott-B07421; > > > >> Bhushan > > > >> Bharat-R65777 > > > >> Subject: Re: [PATCH 4/4 v2] KVM: PPC: Add userspace debug stub > > > >> support > > > >> > > > >> > > > >> How does the normal debug register switching code work in Linux? > > > >> Can't we just reuse that? Or rely on it to restore working state > > when > > > >> another process gets scheduled in? > > > > > > > > Good point, I can see debug registers loading in function > > __switch_to()- > > > >switch_booke_debug_regs() in file arch/powerpc/kernel/process.c. > > > > So as long as assume that host will not use debug resources we > > can rely on > > > this restore. But I am not sure that this is a fare assumption. As > > Scott earlier > > > mentioned someone can use debug resource for kernel debugging also. > > > > > > Someone in the kernel can also use floating point registers. But > > then it's his > > > responsibility to clean up the mess he leaves behind. > > > > I am neither convinced by what you said and nor even have much reason > > to oppose :) > > > > Scott, > > I remember you mentioned that host can use debug resources, you > > comment on this ? > > I thought the conclusion we reached was that it was OK as long as KVM waits > until it actually needs the debug resources to mess with the registers. Right, Are we also agreeing on that KVM will not save/restore host debug context on vcpu_load/vcpu_put()? KVM will load its context in vcpu_load() if needed and on vcpu_put() it will clear DBCR0 and DBSR. Thanks -Bharat -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
