> -----Original Message-----
> From: Alexander Graf [mailto:ag...@suse.de]
> Sent: Thursday, July 17, 2014 9:41 PM
> To: Bhushan Bharat-R65777; kvm-...@vger.kernel.org
> Cc: kvm@vger.kernel.org; Wood Scott-B07421; Yoder Stuart-B08248
> Subject: Re: [PATCH] kvm: ppc: booke: Restore SPRG3 when entering guest
> 
> 
> On 16.07.14 08:02, Bharat Bhushan wrote:
> > SPRG3 is guest accessible and SPRG3 can be clobbered by host or
> > another guest, So this need to be restored when loading guest state.
> >
> > Signed-off-by: Bharat Bhushan <bharat.bhus...@freescale.com>
> > ---
> >   arch/powerpc/kvm/booke_interrupts.S | 2 ++
> >   1 file changed, 2 insertions(+)
> >
> > diff --git a/arch/powerpc/kvm/booke_interrupts.S
> > b/arch/powerpc/kvm/booke_interrupts.S
> > index 2c6deb5ef..0d3403f 100644
> > --- a/arch/powerpc/kvm/booke_interrupts.S
> > +++ b/arch/powerpc/kvm/booke_interrupts.S
> > @@ -459,6 +459,8 @@ lightweight_exit:
> >      * written directly to the shared area, so we
> >      * need to reload them here with the guest's values.
> >      */
> > +   PPC_LD(r3, VCPU_SHARED_SPRG3, r5)
> > +   mtspr   SPRN_SPRG3, r3
> 
> We also need to restore it when resuming the host, no?

I do not think host expect some meaningful value when returning from guest, 
same true for SPRG4-7.
So there seems no reason to save host values and restore them.

Thanks
-Bharat
> 
> 
> Alex
> 
> >     PPC_LD(r3, VCPU_SHARED_SPRG4, r5)
> >     mtspr   SPRN_SPRG4W, r3
> >     PPC_LD(r3, VCPU_SHARED_SPRG5, r5)

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