Re: [PATCH] powerpc: Fix booting P9 hash with CONFIG_PPC_RADIX_MMU=N

[Michael Neuling <mikey@neuling.org>]

On Thu, 2017-05-25 at 08:23 +0530, Aneesh Kumar K.V wrote:
> Michael Neuling <mikey@neuling.org> writes:
>=20
> > On Wed, 2017-05-24 at 14:26 +0530, Aneesh Kumar K.V wrote:
> > > Michael Neuling <mikey@neuling.org> writes:
> > >=20
> > > > Currently if you disable CONFIG_PPC_RADIX_MMU you'll crash on boot =
on
> > > > a P9. This is because we still set MMU_FTR_TYPE_RADIX via
> > > > ibm,pa-features and MMU_FTR_TYPE_RADIX is what's used for code patc=
hing
> > > > in much of the asm code (ie. slb_miss_realmode)
> > > >=20
> > > > This patch fixes the problem by stopping MMU_FTR_TYPE_RADIX from be=
ing
> > > > set from ibm.pa-features.
> > > >=20
> > > > We may eventually end up removing the CONFIG_PPC_RADIX_MMU option
> > > > completely but until then this fixes the issue.
> > > >=20
> > > > Signed-off-by: Michael Neuling <mikey@neuling.org>
> > > > ---
> > > > =C2=A0arch/powerpc/kernel/prom.c | 2 ++
> > > > =C2=A01 file changed, 2 insertions(+)
> > > >=20
> > > > diff --git a/arch/powerpc/kernel/prom.c b/arch/powerpc/kernel/prom.=
c
> > > > index 40c4887c27..f830562974 100644
> > > > --- a/arch/powerpc/kernel/prom.c
> > > > +++ b/arch/powerpc/kernel/prom.c
> > > > @@ -161,7 +161,9 @@ static struct ibm_pa_feature {
> > > > =C2=A0	{ .pabyte =3D 0,=C2=A0=C2=A0.pabit =3D 3, .cpu_features=C2=
=A0=C2=A0=3D CPU_FTR_CTRL },
> > > > =C2=A0	{ .pabyte =3D 0,=C2=A0=C2=A0.pabit =3D 6, .cpu_features=C2=
=A0=C2=A0=3D CPU_FTR_NOEXECUTE
> > > > },
> > > > =C2=A0	{ .pabyte =3D 1,=C2=A0=C2=A0.pabit =3D 2, .mmu_features=C2=
=A0=C2=A0=3D
> > > > MMU_FTR_CI_LARGE_PAGE
> > > > },
> > > > +#ifdef CONFIG_PPC_RADIX_MMU
> > > > =C2=A0	{ .pabyte =3D 40, .pabit =3D 0, .mmu_features=C2=A0=C2=A0=3D=
 MMU_FTR_TYPE_RADIX
> > > > },
> > > > +#endif
> > > > =C2=A0	{ .pabyte =3D 1,=C2=A0=C2=A0.pabit =3D 1, .invert =3D 1, .cp=
u_features =3D
> > > > CPU_FTR_NODSISRALIGN },
> > > > =C2=A0	{ .pabyte =3D 5,=C2=A0=C2=A0.pabit =3D 0, .cpu_features=C2=
=A0=C2=A0=3D CPU_FTR_REAL_LE,
> > > > =C2=A0				=C2=A0=C2=A0=C2=A0=C2=A0.cpu_user_ftrs =3D
> > > > PPC_FEATURE_TRUE_LE },
> > > > --=C2=A0
> > > > 2.11.0
> > >=20
> > > Instead can we do that feature removal in mmu_early_init_devtree. ie,
> > > something like
> >=20
> > It looks like mmu_early_init_devtree() gets called after parsing
> > ibm,pa_features
> > so that should work.
> >=20
> > > diff --git a/arch/powerpc/mm/init_64.c b/arch/powerpc/mm/init_64.c
> > > index 8f6f2a173e47..8f43f3827bac 100644
> > > --- a/arch/powerpc/mm/init_64.c
> > > +++ b/arch/powerpc/mm/init_64.c
> > > @@ -394,7 +394,7 @@ void __init mmu_early_init_devtree(v
> > > oid)
> > > =C2=A0{
> > > =C2=A0	/* Disable radix mode based on kernel command line. */
> > > =C2=A0	/* We don't yet have the machinery to do radix as a guest. */
> > > -	if (disable_radix || !(mfmsr() & MSR_HV))
> > > > +	if (!IS_ENABLED(CONFIG_PPC_RADIX_MMU) || disable_radix ||
> > > > !(mfmsr() & MSR_HV))
> >=20
> > What tree is this patch against?=C2=A0=C2=A0Linus' tree doesn't look li=
ke that.
> >=20
>=20
> mpe/next at the time of this merge window. Do you want me to send a
> complete patch against latest mpe/next ?

If you can test the broken case to make sure it fixes it... Sure!

Thanks,
Mikey