Re: [PATCH] mm/zsmalloc.c: Fix zsmalloc 32-bit PAE support

diff --git a/arch/x86/include/asm/pgtable_64_types.h b/arch/x86/include/asm/pgtable_64_types.h
index 84bd9bdc1987..d808cfde3d19 100644
--- a/arch/x86/include/asm/pgtable_64_types.h
+++ b/arch/x86/include/asm/pgtable_64_types.h

@@ -64,8 +64,6 @@ extern unsigned int ptrs_per_p4d;
 #define P4D_SIZE		(_AC(1, UL) << P4D_SHIFT)
 #define P4D_MASK		(~(P4D_SIZE - 1))
 
-#define MAX_POSSIBLE_PHYSMEM_BITS	52
-
 #else /* CONFIG_X86_5LEVEL */
 
 /*

@@ -154,4 +152,6 @@ extern unsigned int ptrs_per_p4d;
 
 #define PGD_KERNEL_START	((PAGE_SIZE / 2) / sizeof(pgd_t))
 
+#define MAX_POSSIBLE_PHYSMEM_BITS (pgtable_l5_enabled() ? 52 : 46)
+

 #endif /* _ASM_X86_PGTABLE_64_DEFS_H */

diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index 0787d33b80d8..132c20b6fd4f 100644
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c

@@ -116,6 +100,25 @@
  */
 #define OBJ_ALLOCATED_TAG 1
 #define OBJ_TAG_BITS 1
+
+/*
+ * MAX_POSSIBLE_PHYSMEM_BITS should be defined by all archs using zsmalloc:
+ * Trying to guess it from MAX_PHYSMEM_BITS, or considering it BITS_PER_LONG,
+ * proved to be wrong by not considering PAE capabilities, or using SPARSEMEM
+ * only headers, leading to bad object encoding due to object index overflow.
+ */
+#ifndef MAX_POSSIBLE_PHYSMEM_BITS
+ #define MAX_POSSIBLE_PHYSMEM_BITS BITS_PER_LONG
+ #error "MAX_POSSIBLE_PHYSMEM_BITS HAS to be defined by arch using zsmalloc";
+#else
+ #ifndef CONFIG_64BIT
+  #if (MAX_POSSIBLE_PHYSMEM_BITS >= (BITS_PER_LONG + PAGE_SHIFT - OBJ_TAG_BITS))
+   #error "MAX_POSSIBLE_PHYSMEM_BITS is wrong for this arch";
+  #endif
+ #endif
+#endif
+
+#define _PFN_BITS (MAX_POSSIBLE_PHYSMEM_BITS - PAGE_SHIFT)
 #define OBJ_INDEX_BITS	(BITS_PER_LONG - _PFN_BITS - OBJ_TAG_BITS)
 #define OBJ_INDEX_MASK	((_AC(1, UL) << OBJ_INDEX_BITS) - 1)