linux-kernel - [PATCH 1/3] fixup mmu_features immediately after getting cpu pa features.

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Message-Id: <20211008161552.211262-2-sourabhjain@linux.ibm.com>
Date:   Fri,  8 Oct 2021 21:45:50 +0530
From:   Sourabh Jain <sourabhjain@...ux.ibm.com>
To:     linux-kernel@...r.kernel.org
Cc:     hbathini@...ux.ibm.com, mahesh@...ux.vnet.ibm.com,
        mpe@...erman.id.au, linuxppc-dev@...abs.org,
        aneesh.kumar@...ux.ibm.com,
        Mahesh Salgaonkar <mahesh@...ux.ibm.com>,
        Abdul haleem <abdhalee@...ux.vnet.ibm.com>
Subject: [PATCH 1/3] fixup mmu_features immediately after getting cpu pa features.

From: Mahesh Salgaonkar <mahesh@...ux.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.

Withi 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@...ux.ibm.com>
Signed-off-by: Sourabh Jain <sourabhjain@...ux.ibm.com>
Reported-and-tested-by: Abdul haleem <abdhalee@...ux.vnet.ibm.com>
---
 arch/powerpc/include/asm/book3s/64/mmu.h | 1 +
 arch/powerpc/include/asm/mmu.h           | 1 +
 arch/powerpc/kernel/prom.c               | 2 ++
 arch/powerpc/mm/init_64.c                | 5 ++++-
 4 files changed, 8 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..d60be5051d60 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 update_cpu_features(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..5eb494ea85d7 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 update_cpu_features(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..889c909e4ed4 100644
--- a/arch/powerpc/kernel/prom.c
+++ b/arch/powerpc/kernel/prom.c
@@ -380,6 +380,8 @@ static int __init early_init_dt_scan_cpus(unsigned long node,
 		check_cpu_pa_features(node);
 	}
 
+	/* Update cpu features based on kernel command line */
+	update_cpu_features();
 	identical_pvr_fixup(node);
 	init_mmu_slb_size(node);
 
diff --git a/arch/powerpc/mm/init_64.c b/arch/powerpc/mm/init_64.c
index 386be136026e..19680b42898f 100644
--- a/arch/powerpc/mm/init_64.c
+++ b/arch/powerpc/mm/init_64.c
@@ -437,12 +437,15 @@ static void __init early_check_vec5(void)
 	}
 }
 
-void __init mmu_early_init_devtree(void)
+void __init update_cpu_features(void)
 {
 	/* Disable radix mode based on kernel command line. */
 	if (disable_radix)
 		cur_cpu_spec->mmu_features &= ~MMU_FTR_TYPE_RADIX;
+}
 
+void __init mmu_early_init_devtree(void)
+{
 	/*
 	 * Check /chosen/ibm,architecture-vec-5 if running as a guest.
 	 * When running bare-metal, we can use radix if we like
-- 
2.31.1