linux-kernel - [PATCH v16 3/4] mm: define default MAX_PTRS_PER

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Date:   Thu, 24 Jun 2021 13:40:49 +1000
From:   Daniel Axtens <dja@...ens.net>
To:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        kasan-dev@...glegroups.com, elver@...gle.com,
        akpm@...ux-foundation.org, andreyknvl@...il.com
Cc:     linuxppc-dev@...ts.ozlabs.org, christophe.leroy@...roup.eu,
        aneesh.kumar@...ux.ibm.com, bsingharora@...il.com,
        Daniel Axtens <dja@...ens.net>
Subject: [PATCH v16 3/4] mm: define default MAX_PTRS_PER_* in include/pgtable.h

Commit c65e774fb3f6 ("x86/mm: Make PGDIR_SHIFT and PTRS_PER_P4D variable")
made PTRS_PER_P4D variable on x86 and introduced MAX_PTRS_PER_P4D as a
constant for cases which need a compile-time constant (e.g. fixed-size
arrays).

powerpc likewise has boot-time selectable MMU features which can cause
other mm "constants" to vary. For KASAN, we have some static
PTE/PMD/PUD/P4D arrays so we need compile-time maximums for all these
constants. Extend the MAX_PTRS_PER_ idiom, and place default definitions
in include/pgtable.h. These define MAX_PTRS_PER_x to be PTRS_PER_x unless
an architecture has defined MAX_PTRS_PER_x in its arch headers.

Clean up pgtable-nop4d.h and s390's MAX_PTRS_PER_P4D definitions while
we're at it: both can just pick up the default now.

Acked-by: Andrey Konovalov <andreyknvl@...il.com>
Reviewed-by: Christophe Leroy <christophe.leroy@...roup.eu>
Reviewed-by: Marco Elver <elver@...gle.com>
Signed-off-by: Daniel Axtens <dja@...ens.net>

---

s390 was compile tested only.
---
 arch/s390/include/asm/pgtable.h     |  2 --
 include/asm-generic/pgtable-nop4d.h |  1 -
 include/linux/pgtable.h             | 22 ++++++++++++++++++++++
 3 files changed, 22 insertions(+), 3 deletions(-)

diff --git a/arch/s390/include/asm/pgtable.h b/arch/s390/include/asm/pgtable.h
index 79742f497cb5..dcac7b2df72c 100644
--- a/arch/s390/include/asm/pgtable.h
+++ b/arch/s390/include/asm/pgtable.h
@@ -343,8 +343,6 @@ static inline int is_module_addr(void *addr)
 #define PTRS_PER_P4D	_CRST_ENTRIES
 #define PTRS_PER_PGD	_CRST_ENTRIES
 
-#define MAX_PTRS_PER_P4D	PTRS_PER_P4D
-
 /*
  * Segment table and region3 table entry encoding
  * (R = read-only, I = invalid, y = young bit):
diff --git a/include/asm-generic/pgtable-nop4d.h b/include/asm-generic/pgtable-nop4d.h
index 2f1d0aad645c..03b7dae47dd4 100644
--- a/include/asm-generic/pgtable-nop4d.h
+++ b/include/asm-generic/pgtable-nop4d.h
@@ -9,7 +9,6 @@
 typedef struct { pgd_t pgd; } p4d_t;
 
 #define P4D_SHIFT		PGDIR_SHIFT
-#define MAX_PTRS_PER_P4D	1
 #define PTRS_PER_P4D		1
 #define P4D_SIZE		(1UL << P4D_SHIFT)
 #define P4D_MASK		(~(P4D_SIZE-1))
diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
index fb20c57de2ce..d147480cdefc 100644
--- a/include/linux/pgtable.h
+++ b/include/linux/pgtable.h
@@ -1634,4 +1634,26 @@ typedef unsigned int pgtbl_mod_mask;
 #define pte_leaf_size(x) PAGE_SIZE
 #endif
 
+/*
+ * Some architectures have MMUs that are configurable or selectable at boot
+ * time. These lead to variable PTRS_PER_x. For statically allocated arrays it
+ * helps to have a static maximum value.
+ */
+
+#ifndef MAX_PTRS_PER_PTE
+#define MAX_PTRS_PER_PTE PTRS_PER_PTE
+#endif
+
+#ifndef MAX_PTRS_PER_PMD
+#define MAX_PTRS_PER_PMD PTRS_PER_PMD
+#endif
+
+#ifndef MAX_PTRS_PER_PUD
+#define MAX_PTRS_PER_PUD PTRS_PER_PUD
+#endif
+
+#ifndef MAX_PTRS_PER_P4D
+#define MAX_PTRS_PER_P4D PTRS_PER_P4D
+#endif
+
 #endif /* _LINUX_PGTABLE_H */
-- 
2.30.2