Re: [Qemu-devel] [PATCH 05/17] ppc: Fix hreg_store_msr() so that non-HV mode cannot alter MSR:HV

[David Gibson <david@gibson.dropbear.id.au>]

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On Mon, Mar 14, 2016 at 08:29:10PM +0100, Thomas Huth wrote:
> On 14.03.2016 17:56, Cédric Le Goater wrote:
> > From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> > 
> > This helper is only used by the various instructions that can alter
> > MSR and not interrupts. Add a comment to that effect to the interrupt
> > code as well in case somebody wants to change this
> > 
> > Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> > Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
> > ---
> >  target-ppc/excp_helper.c | 8 ++++++--
> >  target-ppc/helper_regs.h | 4 ++--
> >  2 files changed, 8 insertions(+), 4 deletions(-)
> > 
> > diff --git a/target-ppc/excp_helper.c b/target-ppc/excp_helper.c
> > index c890853d861b..37d4721db63b 100644
> > --- a/target-ppc/excp_helper.c
> > +++ b/target-ppc/excp_helper.c
> > @@ -666,8 +666,12 @@ static inline void powerpc_excp(PowerPCCPU *cpu, int excp_model, int excp)
> >          }
> >      }
> >  #endif
> > -    /* XXX: we don't use hreg_store_msr here as already have treated
> > -     *      any special case that could occur. Just store MSR and update hflags
> > +    /* We don't use hreg_store_msr here as already have treated
> > +     * any special case that could occur. Just store MSR and update hflags
> > +     *
> > +     * Note: We *MUST* not use hreg_store_msr() as-is anyway because it
> > +     * will prevent setting of the HV bit which some exceptions might need
> > +     * to do.
> >       */
> >      env->msr = new_msr & env->msr_mask;
> >      hreg_compute_hflags(env);
> > diff --git a/target-ppc/helper_regs.h b/target-ppc/helper_regs.h
> > index 271fddf17f0a..844240d1a755 100644
> > --- a/target-ppc/helper_regs.h
> > +++ b/target-ppc/helper_regs.h
> > @@ -75,8 +75,8 @@ static inline int hreg_store_msr(CPUPPCState *env, target_ulong value,
> >      excp = 0;
> >      value &= env->msr_mask;
> >  #if !defined(CONFIG_USER_ONLY)
> > -    if (!alter_hv) {
> > -        /* mtmsr cannot alter the hypervisor state */
> > +    /* Neither mtmsr nor guest state can alter HV */
> > +    if (!alter_hv || !(env->msr & MSR_HVB)) {
> >          value &= ~MSR_HVB;
> >          value |= env->msr & MSR_HVB;
> >      }
> 
> Reviewed-by: Thomas Huth <thuth@redhat.com>

This looks correct, but I'm not seeing a strong case for including it
before 2.6.

-- 
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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