Re: [Qemu-devel] [RFC PATCH 16/26] ppc/xive: notify CPU when interrupt priority is more privileged

[Benjamin Herrenschmidt <benh@kernel.crashing.org>]

On Sat, 2017-09-09 at 10:08 +0200, Cédric Le Goater wrote:
> On 09/09/2017 09:39 AM, Benjamin Herrenschmidt wrote:
> > On Wed, 2017-07-05 at 19:13 +0200, Cédric Le Goater wrote:
> > > Signed-off-by: Cédric Le Goater <clg@kaod.org>
> > > ---
> > >  hw/intc/xive.c | 21 +++++++++++++++++++++
> > >  1 file changed, 21 insertions(+)
> > > 
> > > diff --git a/hw/intc/xive.c b/hw/intc/xive.c
> > > index c3c1e9c9db2d..cda1fa18e44d 100644
> > > --- a/hw/intc/xive.c
> > > +++ b/hw/intc/xive.c
> > > @@ -53,6 +53,21 @@ static uint64_t xive_icp_accept(XiveICPState *xicp)
> > >      return (nsr << 8) | xicp->tima_os[TM_CPPR];
> > >  }
> > >  
> > > +static uint8_t ipb_to_pipr(uint8_t ibp)
> > > +{
> > > +    return ibp ? clz32((uint32_t)ibp << 24) : 0xff;
> > > +}
> > 
> > The PIPR needs to be updated also on accept etc... anything that change
> > IPBs or CPPR really.
> 
> I did forget the update in accept ... thanks. 
> 
> > Also I just learned something from the designers: The IPIR is clamped
> > to CPPR.
> > 
> > So basically the value in the PIPR is:
> > 
> > 	v = leftmost_bit_of(ipb) (or 0xff);
> > 	pipr = v < cppr ? v : cppr;
> > 
> > which means it's never actually 0xff ... surprise !
> 
> ah. that is not what the specs say but it shouldn't be a problem.
> I will change the code to reflect that.

Right, I've asked the HW guys to update the spec.

Cheers,
Ben.

> C.
> 
> > That also means I need to fix my implementation of H_IPOLL in KVM.
> > 
> > > +static void xive_icp_notify(XiveICPState *xicp)
> > > +{
> > > +    xicp->tima_os[TM_PIPR] = ipb_to_pipr(xicp->tima_os[TM_IPB]);
> > > +
> > > +    if (xicp->tima_os[TM_PIPR] < xicp->tima_os[TM_CPPR]) {
> > > +        xicp->tima_os[TM_NSR] |= TM_QW1_NSR_EO;
> > > +        qemu_irq_raise(ICP(xicp)->output);
> > > +    }
> > > +}
> > > +
> > >  static void xive_icp_set_cppr(XiveICPState *xicp, uint8_t cppr)
> > >  {
> > >      if (cppr > XIVE_PRIORITY_MAX) {
> > > @@ -60,6 +75,10 @@ static void xive_icp_set_cppr(XiveICPState *xicp, uint8_t cppr)
> > >      }
> > >  
> > >      xicp->tima_os[TM_CPPR] = cppr;
> > > +
> > > +    /* CPPR has changed, inform the ICP which might raise an
> > > +     * exception */
> > > +    xive_icp_notify(xicp);
> > >  }
> > >  
> > >  /*
> > > @@ -339,6 +358,8 @@ static void xive_icp_irq(XiveICSState *xs, int lisn)
> > >      } else {
> > >          qemu_log_mask(LOG_UNIMP, "XIVE: w7 format1 not implemented\n");
> > >      }
> > > +
> > > +    xive_icp_notify(xicp);
> > >  }
> > >  
> > >  /*