RE: [PATCH] kvm: ppc: booke: Restore SPRG3 when entering guest

Bharat.Bhushan
2014-07-17T16:24:39Z

> -----Original Message-----
> From: Alexander Graf [mailto:agraf@suse.de]
> Sent: Thursday, July 17, 2014 9:41 PM
> To: Bhushan Bharat-R65777; kvm-ppc@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.Bhushan@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)