Re: [PATCH 1/3] fixup mmu_features immediately after getting cpu pa features.

On 2021-10-04 21:02:21 Mon, Aneesh Kumar K.V wrote:

On 10/4/21 20:41, Sourabh Jain wrote:

quoted

From: Mahesh Salgaonkar <mahesh@linux.ibm.com>

On system with radix support available, early_radix_enabled() starts
returning true for a small window (until mmu_early_init_devtree() is
called) even when radix mode disabled on kernel command line. This causes
ppc64_bolted_size() to return ULONG_MAX in HPT mode instead of supported
segment size, during boot cpu paca allocation.

With kernel command line = "... disable_radix":

early_init_devtree:			  <- early_radix_enabled() = false
   early_init_dt_scan_cpus:		  <- early_radix_enabled() = false
       ...
       check_cpu_pa_features:		  <- early_radix_enabled() = false
       ...				^ <- early_radix_enabled() = TRUE
       allocate_paca:			| <- early_radix_enabled() = TRUE
           ...                           |
           ppc64_bolted_size:		| <- early_radix_enabled() = TRUE
               if (early_radix_enabled())| <- early_radix_enabled() = TRUE
                   return ULONG_MAX;     |
       ...                               |
   ...					| <- early_radix_enabled() = TRUE
   ...					| <- early_radix_enabled() = TRUE
   mmu_early_init_devtree()              V
   ...					  <- early_radix_enabled() = false

So far we have not seen any issue because allocate_paca() takes minimum of
ppc64_bolted_size and rma_size while allocating paca. However it is better
to close this window by fixing up the mmu features as early as possible.
This fixes early_radix_enabled() and ppc64_bolted_size() to return valid
values in radix disable mode. This patch will help subsequent patch to
depend on early_radix_enabled() check while detecting supported segment
size in HPT mode.

Signed-off-by: Mahesh Salgaonkar <mahesh@linux.ibm.com>
Signed-off-by: Sourabh Jain <redacted>
Reported-and-tested-by: Abdul haleem <redacted>
---
  arch/powerpc/include/asm/book3s/64/mmu.h | 1 +
  arch/powerpc/include/asm/mmu.h           | 1 +
  arch/powerpc/kernel/prom.c               | 1 +
  arch/powerpc/mm/init_64.c                | 5 ++++-
  4 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/include/asm/book3s/64/mmu.h b/arch/powerpc/include/asm/book3s/64/mmu.h
index c02f42d1031e..69a89fa1330d 100644
--- a/arch/powerpc/include/asm/book3s/64/mmu.h
+++ b/arch/powerpc/include/asm/book3s/64/mmu.h

@@ -197,6 +197,7 @@ extern int mmu_vmemmap_psize;
  extern int mmu_io_psize;
  /* MMU initialization */
+void mmu_cpu_feature_fixup(void);
  void mmu_early_init_devtree(void);
  void hash__early_init_devtree(void);
  void radix__early_init_devtree(void);

diff --git a/arch/powerpc/include/asm/mmu.h b/arch/powerpc/include/asm/mmu.h
index 8abe8e42e045..c8eafd401fe9 100644
--- a/arch/powerpc/include/asm/mmu.h
+++ b/arch/powerpc/include/asm/mmu.h

@@ -401,6 +401,7 @@ extern void early_init_mmu(void);
  extern void early_init_mmu_secondary(void);
  extern void setup_initial_memory_limit(phys_addr_t first_memblock_base,
  				       phys_addr_t first_memblock_size);
+static inline void mmu_cpu_feature_fixup(void) { }
  static inline void mmu_early_init_devtree(void) { }
  static inline void pkey_early_init_devtree(void) {}

diff --git a/arch/powerpc/kernel/prom.c b/arch/powerpc/kernel/prom.c
index 2e67588f6f6e..1727a3abe6c1 100644
--- a/arch/powerpc/kernel/prom.c
+++ b/arch/powerpc/kernel/prom.c

@@ -380,6 +380,7 @@ static int __init early_init_dt_scan_cpus(unsigned long node,
  		check_cpu_pa_features(node);
  	}
+	mmu_cpu_feature_fixup();

can you do that call inside check_cpu_pa_features? or is it because we have
the same issue with baremetal platforms?

Yup same issue exist on baremetal as well in case of dt_cpu_ftrs_in_use
is true. Hence calling it after the if (!dt_cpu_ftrs_in_use) code block
takes care of both pseries and baremetal platforms.

Can we also rename this to indicate we are sanitizing the feature flag based
on kernel command line.  Something like

/* Update cpu features based on kernel command line */
update_cpu_features();

Sure will do.

Thanks for your review.
-Mahesh.