x86/mm: Initialize PGD cache during mm initialization

Poking-mm initialization might require to duplicate the PGD in early
stage. Initialize the PGD cache earlier to prevent boot failures.

Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Nadav Amit <namit@vmware.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rick Edgecombe <rick.p.edgecombe@intel.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: 4fc1970 ("x86/alternatives: Initialize temporary mm for patching")
Link: http://lkml.kernel.org/r/20190505011124.39692-1-namit@vmware.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/mm/pgtable.c

@@ -373,14 +373,14 @@ static void pgd_prepopulate_user_pmd(struct mm_struct *mm,
 
 static struct kmem_cache *pgd_cache;
 
-static int __init pgd_cache_init(void)
+void __init pgd_cache_init(void)
 {
 	/*
 	 * When PAE kernel is running as a Xen domain, it does not use
 	 * shared kernel pmd. And this requires a whole page for pgd.
 	 */
 	if (!SHARED_KERNEL_PMD)
-		return 0;
+		return;
 
 	/*
 	 * when PAE kernel is not running as a Xen domain, it uses
@@ -390,9 +390,7 @@ static int __init pgd_cache_init(void)
 	 */
 	pgd_cache = kmem_cache_create("pgd_cache", PGD_SIZE, PGD_ALIGN,
 				      SLAB_PANIC, NULL);
-	return 0;
 }
-core_initcall(pgd_cache_init);
 
 static inline pgd_t *_pgd_alloc(void)
 {
@@ -420,6 +418,10 @@ static inline void _pgd_free(pgd_t *pgd)
 }
 #else
 
+void __init pgd_cache_init(void)
+{
+}
+
 static inline pgd_t *_pgd_alloc(void)
 {
 	return (pgd_t *)__get_free_pages(PGALLOC_GFP, PGD_ALLOCATION_ORDER);

include/asm-generic/pgtable.h

@@ -1126,6 +1126,8 @@ int phys_mem_access_prot_allowed(struct file *file, unsigned long pfn,
 static inline void init_espfix_bsp(void) { }
 #endif
 
+extern void __init pgd_cache_init(void);
+
 #ifndef __HAVE_ARCH_PFN_MODIFY_ALLOWED
 static inline bool pfn_modify_allowed(unsigned long pfn, pgprot_t prot)
 {

init/main.c

@@ -506,6 +506,8 @@ void __init __weak mem_encrypt_init(void) { }
 
 void __init __weak poking_init(void) { }
 
+void __init __weak pgd_cache_init(void) { }
+
 bool initcall_debug;
 core_param(initcall_debug, initcall_debug, bool, 0644);
 
@@ -537,6 +539,7 @@ static void __init mm_init(void)
 	init_espfix_bsp();
 	/* Should be run after espfix64 is set up. */
 	pti_init();
+	pgd_cache_init();
 }
 
 void __init __weak arch_call_rest_init(void)