On Thursday 25 May 2017 11:46 AM, Michael Ellerman wrote:

Michael Neuling [off-list ref] writes:

quoted

On Wed, 2017-05-24 at 14:26 +0530, Aneesh Kumar K.V wrote:

quoted

Michael Neuling [off-list ref] writes:

quoted

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 patching
in much of the asm code (ie. slb_miss_realmode)

This patch fixes the problem by stopping MMU_FTR_TYPE_RADIX from being
set from ibm.pa-features.

We may eventually end up removing the CONFIG_PPC_RADIX_MMU option
completely but until then this fixes the issue.

Signed-off-by: Michael Neuling <redacted>
---
  arch/powerpc/kernel/prom.c | 2 ++
  1 file changed, 2 insertions(+)

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 {
  	{ .pabyte = 0,  .pabit = 3, .cpu_features  = CPU_FTR_CTRL },
  	{ .pabyte = 0,  .pabit = 6, .cpu_features  = CPU_FTR_NOEXECUTE },
  	{ .pabyte = 1,  .pabit = 2, .mmu_features  = MMU_FTR_CI_LARGE_PAGE

},
+#ifdef CONFIG_PPC_RADIX_MMU
  	{ .pabyte = 40, .pabit = 0, .mmu_features  = MMU_FTR_TYPE_RADIX },
+#endif
  	{ .pabyte = 1,  .pabit = 1, .invert = 1, .cpu_features =
CPU_FTR_NODSISRALIGN },
  	{ .pabyte = 5,  .pabit = 0, .cpu_features  = CPU_FTR_REAL_LE,
  				    .cpu_user_ftrs = PPC_FEATURE_TRUE_LE },
-- 
2.11.0

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

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

But why is doing it later preferable?

Mikey's patch means it will never be set at any point during boot, which
seems obviously better to me.

My suggestion was w.r.t consolidating different ways of clearing 
RADIX_MMU feature flag into one place. Also I was not sure we want to 
conditionally parse the pa-feature device tree. Instead we parse it 
without any #ifdef in there and clear things which are not supported by 
the kernel either via command line or via Kconfig.

-aneesh