Re: [Qemu-devel] [Qemu-ppc] [PATCH 2/3] ppc: allow system reset interrupt to be delivered to guests

[David Gibson]

On Fri, Oct 21, 2016 at 12:40:58AM +1100, Nicholas Piggin wrote:
> On Thu, 20 Oct 2016 15:08:07 +0200
> Cédric Le Goater <address@hidden> wrote:
> 
> > On 10/20/2016 08:59 AM, Nicholas Piggin wrote:
> > > Signed-off-by: Nicholas Piggin <address@hidden>
> > > ---
> > >  target-ppc/excp_helper.c | 8 ++++++--
> > >  1 file changed, 6 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/target-ppc/excp_helper.c b/target-ppc/excp_helper.c
> > > index 53c4075..477af10 100644
> > > --- a/target-ppc/excp_helper.c
> > > +++ b/target-ppc/excp_helper.c
> > > @@ -390,9 +390,13 @@ static inline void powerpc_excp(PowerPCCPU *cpu, int 
> > > excp_model, int excp)
> > >              /* indicate that we resumed from power save mode */
> > >              msr |= 0x10000;
> > >              new_msr |= ((target_ulong)1 << MSR_ME);
> > > +            new_msr |= (target_ulong)MSR_HVB;
> > > +        } else {
> > > +     /* The ISA specifies the HV bit is set when the hardware interrupt
> > > +      * is raised, however when hypervisors deliver the exception to
> > > +      * guests, it should not be set.
> > > +      */
> > >          }
> > > -
> > > -        new_msr |= (target_ulong)MSR_HVB;
> > >          ail = 0;
> > >          break;
> > >      case POWERPC_EXCP_DSEG:      /* Data segment exception               
> > >     */
> > >   
> > 
> > should not that be cleared later on in powerpc_excp() by :
> > 
> >     env->msr = new_msr & env->msr_mask;
> > 
> > ? but the routine is rather long so I might be missing a branch.
> 
> No you're right, so it can't leak into the guest, phew!
> 
> The problem I get is the interrupt code doing some things differently
> depending on on the HV bit. For example what I noticed is the guest
> losing its LE bit upon entry.
> 
> Perhaps a cleaner way is for the system reset case to set new_msr
> according to the ISA, and then apply the msr_mask (or at least mask
> out HV) before calculating the exception model? Any preference?

I think the proposed revision makes sense.

-- 
David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!
http://www.ozlabs.org/~dgibson

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