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

On Thu, 2017-05-25 at 08:23 +0530, Aneesh Kumar K.V wrote:

Michael Neuling [off-list ref] writes:
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On Wed, 2017-05-24 at 14:26 +0530, Aneesh Kumar K.V wrote:

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Michael Neuling [off-list ref] writes:
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Currently if you disable CONFIG_PPC_RADIX_MMU you'll crash on boot =

on

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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

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in much of the asm code (ie. slb_miss_realmode)
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This patch fixes the problem by stopping MMU_FTR_TYPE_RADIX from be=

ing

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set from ibm.pa-features.
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We may eventually end up removing the CONFIG_PPC_RADIX_MMU option
completely but until then this fixes the issue.
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Signed-off-by: Michael Neuling <redacted>
---
=C2=A0arch/powerpc/kernel/prom.c | 2 ++
=C2=A01 file changed, 2 insertions(+)
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diff --git a/arch/powerpc/kernel/prom.c b/arch/powerpc/kernel/prom.=

c

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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 },

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=C2=A0	{ .pabyte =3D 0,=C2=A0=C2=A0.pabit =3D 6, .cpu_features=C2=

=A0=C2=A0=3D CPU_FTR_NOEXECUTE

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},
=C2=A0	{ .pabyte =3D 1,=C2=A0=C2=A0.pabit =3D 2, .mmu_features=C2=

=A0=C2=A0=3D

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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

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},
+#endif
=C2=A0	{ .pabyte =3D 1,=C2=A0=C2=A0.pabit =3D 1, .invert =3D 1, .cp=

u_features =3D

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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,

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=C2=A0				=C2=A0=C2=A0=C2=A0=C2=A0.cpu_user_ftrs =3D
PPC_FEATURE_TRUE_LE },
--=C2=A0
2.11.0

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Instead can we do that feature removal in mmu_early_init_devtree. ie,
something like

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It looks like mmu_early_init_devtree() gets called after parsing
ibm,pa_features
so that should work.
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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))

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+	if (!IS_ENABLED(CONFIG_PPC_RADIX_MMU) || disable_radix ||
!(mfmsr() & MSR_HV))

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What tree is this patch against?=C2=A0=C2=A0Linus' tree doesn't look li=

ke that.

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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