Re: [Qemu-ppc] [QEMU-PPC] [PATCH 2/3] target/ppc: Don't require private l1d cache on POWER8 for cap_ppc_safe_cache

[Greg Kurz]

On Fri, 11 May 2018 12:21:11 -0300
Murilo Opsfelder Araujo <address@hidden> wrote:

> On Fri, May 11, 2018 at 04:25:08PM +1000, Suraj Jitindar Singh wrote:
> > For cap_ppc_safe_cache to be set to workaround, we require both a l1d
> > cache flush instruction and private l1d cache.
> > 
> > On POWER8 don't require private l1d cache. This means a guest on a
> > POWER8 machine can make use of the cache flush workarounds.
> > 
> > Signed-off-by: Suraj Jitindar Singh <address@hidden>
> > ---
> >  target/ppc/kvm.c | 10 +++++++++-
> >  1 file changed, 9 insertions(+), 1 deletion(-)
> > 
> > diff --git a/target/ppc/kvm.c b/target/ppc/kvm.c
> > index 2c0c34e125..7b33119b1a 100644
> > --- a/target/ppc/kvm.c
> > +++ b/target/ppc/kvm.c
> > @@ -2414,9 +2414,17 @@ bool kvmppc_has_cap_mmu_hash_v3(void)
> >  
> >  static int parse_cap_ppc_safe_cache(struct kvm_ppc_cpu_char c)
> >  {
> > +    PowerPCCPUClass *pcc = kvm_ppc_get_host_cpu_class();
> > +    bool l1d_thread_priv_req = true;
> > +
> > +    if (pcc->pvr_match(pcc, CPU_POWERPC_POWER8_BASE)) {
> > +        l1d_thread_priv_req = false;
> > +    }
> > +  
> 
> Hi, Suraj.
> 
> Why not use ppc_pvr_match_power8()?
> 

ppc_pvr_match_power8() is the implementation of PowerPCCPUClass::pvr_match()
for the POWER8 family, hence always returns true if passed CPU_POWERPC_POWER8_*

static bool ppc_pvr_match_power8(PowerPCCPUClass *pcc, uint32_t pvr)
{
    if ((pvr & CPU_POWERPC_POWER_SERVER_MASK) == CPU_POWERPC_POWER8NVL_BASE) {
        return true;
    }
    if ((pvr & CPU_POWERPC_POWER_SERVER_MASK) == CPU_POWERPC_POWER8E_BASE) {
        return true;
    }
    if ((pvr & CPU_POWERPC_POWER_SERVER_MASK) == CPU_POWERPC_POWER8_BASE) {
        return true;
    }
    return false;
}

It's the other way round, we want to guess that the host CPU belongs to the
POWER8 family because only its pvr_match() returns true IIUC.

Suraj,

So this is ok for POWER8, POWER8E and POWER8NVL ? If so, it would be
more appropriate to call pcc->pvr_match() for each pvr value IMHO.

> >      if (~c.behaviour & c.behaviour_mask & H_CPU_BEHAV_L1D_FLUSH_PR) {
> >          return 2;
> > -    } else if ((c.character & c.character_mask & 
> > H_CPU_CHAR_L1D_THREAD_PRIV) &&
> > +    } else if ((!l1d_thread_priv_req ||
> > +                c.character & c.character_mask & 
> > H_CPU_CHAR_L1D_THREAD_PRIV) &&
> >                 (c.character & c.character_mask
> >                  & (H_CPU_CHAR_L1D_FLUSH_ORI30 | 
> > H_CPU_CHAR_L1D_FLUSH_TRIG2))) {
> >          return 1;
> > -- 
> > 2.13.6
> > 
> >   
>