asm-generic: pgalloc: provide generic __pgd_{alloc,free}

We already have a generic implementation of alloc/free up to P4D level, as
well as pgd_free().  Let's finish the work and add a generic PGD-level
alloc helper as well.

Unlike at lower levels, almost all architectures need some specific magic
at PGD level (typically initialising PGD entries), so introducing a
generic pgd_alloc() isn't worth it.  Instead we introduce two new helpers,
__pgd_alloc() and __pgd_free(), and make use of them in the arch-specific
pgd_alloc() and pgd_free() wherever possible.  To accommodate as many arch
as possible, __pgd_alloc() takes a page allocation order.

Because pagetable_alloc() allocates zeroed pages, explicit zeroing in
pgd_alloc() becomes redundant and we can get rid of it.  Some trivial
implementations of pgd_free() also become unnecessary once __pgd_alloc()
is used; remove them.

Another small improvement is consistent accounting of PGD pages by using
GFP_PGTABLE_{USER,KERNEL} as appropriate.

Not all PGD allocations can be handled by the generic helpers.  In
particular, multiple architectures allocate PGDs from a kmem_cache, and
those PGDs may not be page-sized.

Link: https://lkml.kernel.org/r/20250103184415.2744423-6-kevin.brodsky@arm.com
Signed-off-by: Kevin Brodsky <kevin.brodsky@arm.com>
Acked-by: Dave Hansen <dave.hansen@linux.intel.com>
Acked-by: Qi Zheng <zhengqi.arch@bytedance.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Linus Walleij <linus.walleij@linaro.org>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Mike Rapoport (Microsoft) <rppt@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

arch/alpha/mm/init.c

@@ -42,7 +42,7 @@ pgd_alloc(struct mm_struct *mm)
 {
 	pgd_t *ret, *init;
 
-	ret = (pgd_t *)__get_free_page(GFP_KERNEL | __GFP_ZERO);
+	ret = __pgd_alloc(mm, 0);
 	init = pgd_offset(&init_mm, 0UL);
 	if (ret) {
 #ifdef CONFIG_ALPHA_LARGE_VMALLOC

arch/arc/include/asm/pgalloc.h

@@ -53,19 +53,14 @@ static inline void pmd_populate(struct mm_struct *mm, pmd_t *pmd, pgtable_t pte_
 
 static inline pgd_t *pgd_alloc(struct mm_struct *mm)
 {
-	pgd_t *ret = (pgd_t *) __get_free_page(GFP_KERNEL);
+	pgd_t *ret = __pgd_alloc(mm, 0);
 
 	if (ret) {
 		int num, num2;
-		num = USER_PTRS_PER_PGD + USER_KERNEL_GUTTER / PGDIR_SIZE;
-		memzero(ret, num * sizeof(pgd_t));
 
+		num = USER_PTRS_PER_PGD + USER_KERNEL_GUTTER / PGDIR_SIZE;
 		num2 = VMALLOC_SIZE / PGDIR_SIZE;
 		memcpy(ret + num, swapper_pg_dir + num, num2 * sizeof(pgd_t));
-
-		memzero(ret + num + num2,
-			       (PTRS_PER_PGD - num - num2) * sizeof(pgd_t));
-
 	}
 	return ret;
 }

arch/arm/mm/pgd.c

@@ -17,11 +17,11 @@
 #include "mm.h"
 
 #ifdef CONFIG_ARM_LPAE
-#define _pgd_alloc(mm)		kmalloc_array(PTRS_PER_PGD, sizeof(pgd_t), GFP_KERNEL)
+#define _pgd_alloc(mm)		kmalloc_array(PTRS_PER_PGD, sizeof(pgd_t), GFP_KERNEL | __GFP_ZERO)
 #define _pgd_free(mm, pgd)	kfree(pgd)
 #else
-#define _pgd_alloc(mm)		(pgd_t *)__get_free_pages(GFP_KERNEL, 2)
-#define _pgd_free(mm, pgd)	free_pages((unsigned long)pgd, 2)
+#define _pgd_alloc(mm)		__pgd_alloc(mm, 2)
+#define _pgd_free(mm, pgd)	__pgd_free(mm, pgd)
 #endif
 
 /*
@@ -39,8 +39,6 @@ pgd_t *pgd_alloc(struct mm_struct *mm)
 	if (!new_pgd)
 		goto no_pgd;
 
-	memset(new_pgd, 0, USER_PTRS_PER_PGD * sizeof(pgd_t));
-
 	/*
 	 * Copy over the kernel and IO PGD entries
 	 */

arch/arm64/mm/pgd.c

@@ -33,7 +33,7 @@ pgd_t *pgd_alloc(struct mm_struct *mm)
 	gfp_t gfp = GFP_PGTABLE_USER;
 
 	if (pgdir_is_page_size())
-		return (pgd_t *)__get_free_page(gfp);
+		return __pgd_alloc(mm, 0);
 	else
 		return kmem_cache_alloc(pgd_cache, gfp);
 }
@@ -41,7 +41,7 @@ pgd_t *pgd_alloc(struct mm_struct *mm)
 void pgd_free(struct mm_struct *mm, pgd_t *pgd)
 {
 	if (pgdir_is_page_size())
-		free_page((unsigned long)pgd);
+		__pgd_free(mm, pgd);
 	else
 		kmem_cache_free(pgd_cache, pgd);
 }

arch/csky/include/asm/pgalloc.h

@@ -44,7 +44,7 @@ static inline pgd_t *pgd_alloc(struct mm_struct *mm)
 	pgd_t *ret;
 	pgd_t *init;
 
-	ret = (pgd_t *) __get_free_page(GFP_KERNEL);
+	ret = __pgd_alloc(mm, 0);
 	if (ret) {
 		init = pgd_offset(&init_mm, 0UL);
 		pgd_init((unsigned long *)ret);

arch/hexagon/include/asm/pgalloc.h

@@ -22,7 +22,7 @@ static inline pgd_t *pgd_alloc(struct mm_struct *mm)
 {
 	pgd_t *pgd;
 
-	pgd = (pgd_t *)__get_free_page(GFP_KERNEL | __GFP_ZERO);
+	pgd = __pgd_alloc(mm, 0);
 
 	/*
 	 * There may be better ways to do this, but to ensure

arch/loongarch/mm/pgtable.c

@@ -23,11 +23,10 @@ EXPORT_SYMBOL(tlb_virt_to_page);
 
 pgd_t *pgd_alloc(struct mm_struct *mm)
 {
-	pgd_t *init, *ret = NULL;
-	struct ptdesc *ptdesc = pagetable_alloc(GFP_KERNEL & ~__GFP_HIGHMEM, 0);
+	pgd_t *init, *ret;
 
-	if (ptdesc) {
-		ret = (pgd_t *)ptdesc_address(ptdesc);
+	ret = __pgd_alloc(mm, 0);
+	if (ret) {
 		init = pgd_offset(&init_mm, 0UL);
 		pgd_init(ret);
 		memcpy(ret + USER_PTRS_PER_PGD, init + USER_PTRS_PER_PGD,

arch/m68k/include/asm/sun3_pgalloc.h

@@ -43,7 +43,7 @@ static inline pgd_t * pgd_alloc(struct mm_struct *mm)
 {
 	pgd_t *new_pgd;
 
-	new_pgd = (pgd_t *)get_zeroed_page(GFP_KERNEL);
+	new_pgd = __pgd_alloc(mm, 0);
 	memcpy(new_pgd, swapper_pg_dir, PAGE_SIZE);
 	memset(new_pgd, 0, (PAGE_OFFSET >> PGDIR_SHIFT));
 	return new_pgd;

arch/microblaze/include/asm/pgalloc.h

@@ -21,12 +21,7 @@
 
 extern void __bad_pte(pmd_t *pmd);
 
-static inline pgd_t *get_pgd(void)
-{
-	return (pgd_t *)__get_free_pages(GFP_KERNEL|__GFP_ZERO, 0);
-}
-
-#define pgd_alloc(mm)		get_pgd()
+#define pgd_alloc(mm)		__pgd_alloc(mm, 0)
 
 extern pte_t *pte_alloc_one_kernel(struct mm_struct *mm);
 

arch/mips/include/asm/pgalloc.h

@@ -15,7 +15,6 @@
 
 #define __HAVE_ARCH_PMD_ALLOC_ONE
 #define __HAVE_ARCH_PUD_ALLOC_ONE
-#define __HAVE_ARCH_PGD_FREE
 #include <asm-generic/pgalloc.h>
 
 static inline void pmd_populate_kernel(struct mm_struct *mm, pmd_t *pmd,
@@ -49,11 +48,6 @@ static inline void pud_populate(struct mm_struct *mm, pud_t *pud, pmd_t *pmd)
 extern void pgd_init(void *addr);
 extern pgd_t *pgd_alloc(struct mm_struct *mm);
 
-static inline void pgd_free(struct mm_struct *mm, pgd_t *pgd)
-{
-	pagetable_free(virt_to_ptdesc(pgd));
-}
-
 #define __pte_free_tlb(tlb, pte, address)			\
 do {								\
 	pagetable_dtor(page_ptdesc(pte));			\

arch/mips/mm/pgtable.c

@@ -10,12 +10,10 @@
 
 pgd_t *pgd_alloc(struct mm_struct *mm)
 {
-	pgd_t *init, *ret = NULL;
-	struct ptdesc *ptdesc = pagetable_alloc(GFP_KERNEL & ~__GFP_HIGHMEM,
-			PGD_TABLE_ORDER);
+	pgd_t *init, *ret;
 
-	if (ptdesc) {
-		ret = ptdesc_address(ptdesc);
+	ret = __pgd_alloc(mm, PGD_TABLE_ORDER);
+	if (ret) {
 		init = pgd_offset(&init_mm, 0UL);
 		pgd_init(ret);
 		memcpy(ret + USER_PTRS_PER_PGD, init + USER_PTRS_PER_PGD,

arch/nios2/mm/pgtable.c

@@ -11,6 +11,7 @@
 #include <linux/sched.h>
 
 #include <asm/cpuinfo.h>
+#include <asm/pgalloc.h>
 
 /* pteaddr:
  *   ptbase | vpn* | zero
@@ -54,7 +55,7 @@ pgd_t *pgd_alloc(struct mm_struct *mm)
 {
 	pgd_t *ret, *init;
 
-	ret = (pgd_t *) __get_free_page(GFP_KERNEL);
+	ret = __pgd_alloc(mm, 0);
 	if (ret) {
 		init = pgd_offset(&init_mm, 0UL);
 		pgd_init(ret);

arch/openrisc/include/asm/pgalloc.h

@@ -41,15 +41,13 @@ static inline void pmd_populate(struct mm_struct *mm, pmd_t *pmd,
  */
 static inline pgd_t *pgd_alloc(struct mm_struct *mm)
 {
-	pgd_t *ret = (pgd_t *)__get_free_page(GFP_KERNEL);
+	pgd_t *ret = __pgd_alloc(mm, 0);
 
-	if (ret) {
-		memset(ret, 0, USER_PTRS_PER_PGD * sizeof(pgd_t));
+	if (ret)
 		memcpy(ret + USER_PTRS_PER_PGD,
 		       swapper_pg_dir + USER_PTRS_PER_PGD,
 		       (PTRS_PER_PGD - USER_PTRS_PER_PGD) * sizeof(pgd_t));
 
-	}
 	return ret;
 }
 

arch/parisc/include/asm/pgalloc.h

@@ -11,26 +11,12 @@
 #include <asm/cache.h>
 
 #define __HAVE_ARCH_PMD_ALLOC_ONE
-#define __HAVE_ARCH_PGD_FREE
 #include <asm-generic/pgalloc.h>
 
 /* Allocate the top level pgd (page directory) */
 static inline pgd_t *pgd_alloc(struct mm_struct *mm)
 {
-	pgd_t *pgd;
-
-	pgd = (pgd_t *) __get_free_pages(GFP_KERNEL, PGD_TABLE_ORDER);
-	if (unlikely(pgd == NULL))
-		return NULL;
-
-	memset(pgd, 0, PAGE_SIZE << PGD_TABLE_ORDER);
-
-	return pgd;
-}
-
-static inline void pgd_free(struct mm_struct *mm, pgd_t *pgd)
-{
-	free_pages((unsigned long)pgd, PGD_TABLE_ORDER);
+	return __pgd_alloc(mm, PGD_TABLE_ORDER);
 }
 
 #if CONFIG_PGTABLE_LEVELS == 3

arch/riscv/include/asm/pgalloc.h

@@ -130,9 +130,8 @@ static inline pgd_t *pgd_alloc(struct mm_struct *mm)
 {
 	pgd_t *pgd;
 
-	pgd = (pgd_t *)__get_free_page(GFP_KERNEL);
+	pgd = __pgd_alloc(mm, 0);
 	if (likely(pgd != NULL)) {
-		memset(pgd, 0, USER_PTRS_PER_PGD * sizeof(pgd_t));
 		/* Copy kernel mappings */
 		sync_kernel_mappings(pgd);
 	}

arch/um/kernel/mem.c

@@ -214,14 +214,13 @@ void free_initmem(void)
 
 pgd_t *pgd_alloc(struct mm_struct *mm)
 {
-	pgd_t *pgd = (pgd_t *)__get_free_page(GFP_KERNEL);
+	pgd_t *pgd = __pgd_alloc(mm, 0);
 
-	if (pgd) {
-		memset(pgd, 0, USER_PTRS_PER_PGD * sizeof(pgd_t));
+	if (pgd)
 		memcpy(pgd + USER_PTRS_PER_PGD,
 		       swapper_pg_dir + USER_PTRS_PER_PGD,
 		       (PTRS_PER_PGD - USER_PTRS_PER_PGD) * sizeof(pgd_t));
-	}
+
 	return pgd;
 }
 

arch/x86/mm/pgtable.c

@@ -397,15 +397,14 @@ void __init pgtable_cache_init(void)
 				      SLAB_PANIC, NULL);
 }
 
-static inline pgd_t *_pgd_alloc(void)
+static inline pgd_t *_pgd_alloc(struct mm_struct *mm)
 {
 	/*
 	 * If no SHARED_KERNEL_PMD, PAE kernel is running as a Xen domain.
 	 * We allocate one page for pgd.
 	 */
 	if (!SHARED_KERNEL_PMD)
-		return (pgd_t *)__get_free_pages(GFP_PGTABLE_USER,
-						 PGD_ALLOCATION_ORDER);
+		return __pgd_alloc(mm, PGD_ALLOCATION_ORDER);
 
 	/*
 	 * Now PAE kernel is not running as a Xen domain. We can allocate
@@ -414,24 +413,23 @@ static inline pgd_t *_pgd_alloc(void)
 	return kmem_cache_alloc(pgd_cache, GFP_PGTABLE_USER);
 }
 
-static inline void _pgd_free(pgd_t *pgd)
+static inline void _pgd_free(struct mm_struct *mm, pgd_t *pgd)
 {
 	if (!SHARED_KERNEL_PMD)
-		free_pages((unsigned long)pgd, PGD_ALLOCATION_ORDER);
+		__pgd_free(mm, pgd);
 	else
 		kmem_cache_free(pgd_cache, pgd);
 }
 #else
 
-static inline pgd_t *_pgd_alloc(void)
+static inline pgd_t *_pgd_alloc(struct mm_struct *mm)
 {
-	return (pgd_t *)__get_free_pages(GFP_PGTABLE_USER,
-					 PGD_ALLOCATION_ORDER);
+	return __pgd_alloc(mm, PGD_ALLOCATION_ORDER);
 }
 
-static inline void _pgd_free(pgd_t *pgd)
+static inline void _pgd_free(struct mm_struct *mm, pgd_t *pgd)
 {
-	free_pages((unsigned long)pgd, PGD_ALLOCATION_ORDER);
+	__pgd_free(mm, pgd);
 }
 #endif /* CONFIG_X86_PAE */
 
@@ -441,7 +439,7 @@ pgd_t *pgd_alloc(struct mm_struct *mm)
 	pmd_t *u_pmds[MAX_PREALLOCATED_USER_PMDS];
 	pmd_t *pmds[MAX_PREALLOCATED_PMDS];
 
-	pgd = _pgd_alloc();
+	pgd = _pgd_alloc(mm);
 
 	if (pgd == NULL)
 		goto out;
@@ -484,7 +482,7 @@ pgd_t *pgd_alloc(struct mm_struct *mm)
 	if (sizeof(pmds) != 0)
 		free_pmds(mm, pmds, PREALLOCATED_PMDS);
 out_free_pgd:
-	_pgd_free(pgd);
+	_pgd_free(mm, pgd);
 out:
 	return NULL;
 }
@@ -494,7 +492,7 @@ void pgd_free(struct mm_struct *mm, pgd_t *pgd)
 	pgd_mop_up_pmds(mm, pgd);
 	pgd_dtor(pgd);
 	paravirt_pgd_free(mm, pgd);
-	_pgd_free(pgd);
+	_pgd_free(mm, pgd);
 }
 
 /*

arch/xtensa/include/asm/pgalloc.h

@@ -29,7 +29,7 @@
 static inline pgd_t*
 pgd_alloc(struct mm_struct *mm)
 {
-	return (pgd_t*) __get_free_page(GFP_KERNEL | __GFP_ZERO);
+	return __pgd_alloc(mm, 0);
 }
 
 static inline void ptes_clear(pte_t *ptep)

include/asm-generic/pgalloc.h

@@ -258,10 +258,35 @@ static inline void p4d_free(struct mm_struct *mm, p4d_t *p4d)
 
 #endif /* CONFIG_PGTABLE_LEVELS > 4 */
 
+static inline pgd_t *__pgd_alloc_noprof(struct mm_struct *mm, unsigned int order)
+{
+	gfp_t gfp = GFP_PGTABLE_USER;
+	struct ptdesc *ptdesc;
+
+	if (mm == &init_mm)
+		gfp = GFP_PGTABLE_KERNEL;
+	gfp &= ~__GFP_HIGHMEM;
+
+	ptdesc = pagetable_alloc_noprof(gfp, order);
+	if (!ptdesc)
+		return NULL;
+
+	return ptdesc_address(ptdesc);
+}
+#define __pgd_alloc(...)	alloc_hooks(__pgd_alloc_noprof(__VA_ARGS__))
+
+static inline void __pgd_free(struct mm_struct *mm, pgd_t *pgd)
+{
+	struct ptdesc *ptdesc = virt_to_ptdesc(pgd);
+
+	BUG_ON((unsigned long)pgd & (PAGE_SIZE-1));
+	pagetable_free(ptdesc);
+}
+
 #ifndef __HAVE_ARCH_PGD_FREE
 static inline void pgd_free(struct mm_struct *mm, pgd_t *pgd)
 {
-	pagetable_free(virt_to_ptdesc(pgd));
+	__pgd_free(mm, pgd);
 }
 #endif