Re: [Xen-devel] [PATCH] xen/arm: Trap the ACTLR register

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Wed, 17 Jul 2013, Ian Campbell wrote:
> On Thu, 2013-07-04 at 16:01 +0100, Julien Grall wrote:
> > @@ -452,6 +451,12 @@ int vcpu_initialise(struct vcpu *v)
> >          return rc;
> >  
> >      v->arch.sctlr = SCTLR_BASE;
> > +    v->arch.actlr = READ_SYSREG32(ACTLR_EL1);
> > +    /* XXX: Handle other than CA15 cpus */
> > +    if ( v->domain->max_vcpus > 1 )
> > +        v->arch.actlr |= ACTLR_CA15_SMP;
> > +    else
> > +        v->arch.actlr &= ~ACTLR_CA15_SMP;
> 
> I'm not 100% sure about this last bit. A CONFIG_SMP=y kernel will want
> to set this regardless of there only being one processor since the
> Cortex A15 (and now A7) are both MPCore processors. Granted they don't
> actually check or panic etc when we ignore them, so maybe it doesn't
> matter.
> 
> I'd be tempted to simply expose the raw underling ACTLR_EL1 to guests
> (r/o of course), it neatly sidesteps any need to know about specific
> processors too. Anyone got any other thoughts?

The only concern would be about migration or big.LITTLE machines, where
at some point the value of the ACTLR (if it's even present) would
suddenly change underneath Linux's feet.
I don't think that would cause problems, but it's worth keeping it in
mind.


> >  
> >      if ( (rc = vcpu_vgic_init(v)) != 0 )
> >          return rc;
> > diff --git a/xen/arch/arm/traps.c b/xen/arch/arm/traps.c
> > index 398d209..bbd60aa 100644
> > --- a/xen/arch/arm/traps.c
> > +++ b/xen/arch/arm/traps.c
> > @@ -62,7 +62,8 @@ void __cpuinit init_traps(void)
> >      WRITE_SYSREG((vaddr_t)hyp_traps_vector, VBAR_EL2);
> >  
> >      /* Setup hypervisor traps */
> > -    
> > WRITE_SYSREG(HCR_PTW|HCR_BSU_OUTER|HCR_AMO|HCR_IMO|HCR_VM|HCR_TWI|HCR_TSC, 
> > HCR_EL2);
> > +    
> > WRITE_SYSREG(HCR_PTW|HCR_BSU_OUTER|HCR_AMO|HCR_IMO|HCR_VM|HCR_TWI|HCR_TSC|
> > +                 HCR_TAC, HCR_EL2);
> >      isb();
> >  }
> >  
> > @@ -836,6 +837,7 @@ static void do_cp15_32(struct cpu_user_regs *regs,
> >  {
> >      struct hsr_cp32 cp32 = hsr.cp32;
> >      uint32_t *r = (uint32_t*)select_user_reg(regs, cp32.reg);
> > +    struct vcpu *v = current;
> >  
> >      if ( !cp32.ccvalid ) {
> >          dprintk(XENLOG_ERR, "cp_15(32): need to handle invalid condition 
> > codes\n");
> > @@ -889,6 +891,10 @@ static void do_cp15_32(struct cpu_user_regs *regs,
> >              domain_crash_synchronous();
> >          }
> >          break;
> > +    case HSR_CPREG32(ACTLR):
> > +        if ( cp32.read )
> > +           *r = v->arch.actlr;
> > +        break;
> >      default:
> >          printk("%s p15, %d, r%d, cr%d, cr%d, %d @ 0x%"PRIregister"\n",
> >                 cp32.read ? "mrc" : "mcr",
> 
> 

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