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.
-Scott
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