[PATCH v1 14/16] mm/vmalloc: Batch arch_sync_kernel_mappings() more efficiently

[Ryan Roberts <ryan.roberts@arm.com>]

When page_shift is greater than PAGE_SIZE, __vmap_pages_range_noflush()
will call vmap_range_noflush() for each individual huge page. But
vmap_range_noflush() would previously call arch_sync_kernel_mappings()
directly so this would end up being called for every huge page.

We can do better than this; refactor the call into the outer
__vmap_pages_range_noflush() so that it is only called once for the
entire batch operation.

This will benefit performance for arm64 which is about to opt-in to
using the hook.

Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
---
 mm/vmalloc.c | 60 ++++++++++++++++++++++++++--------------------------
 1 file changed, 30 insertions(+), 30 deletions(-)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 68950b1824d0..50fd44439875 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -285,40 +285,38 @@ static int vmap_p4d_range(pgd_t *pgd, unsigned long addr, unsigned long end,
 
 static int vmap_range_noflush(unsigned long addr, unsigned long end,
 			phys_addr_t phys_addr, pgprot_t prot,
-			unsigned int max_page_shift)
+			unsigned int max_page_shift, pgtbl_mod_mask *mask)
 {
 	pgd_t *pgd;
-	unsigned long start;
 	unsigned long next;
 	int err;
-	pgtbl_mod_mask mask = 0;
 
 	might_sleep();
 	BUG_ON(addr >= end);
 
-	start = addr;
 	pgd = pgd_offset_k(addr);
 	do {
 		next = pgd_addr_end(addr, end);
 		err = vmap_p4d_range(pgd, addr, next, phys_addr, prot,
-					max_page_shift, &mask);
+					max_page_shift, mask);
 		if (err)
 			break;
 	} while (pgd++, phys_addr += (next - addr), addr = next, addr != end);
 
-	if (mask & ARCH_PAGE_TABLE_SYNC_MASK)
-		arch_sync_kernel_mappings(start, end);
-
 	return err;
 }
 
 int vmap_page_range(unsigned long addr, unsigned long end,
 		    phys_addr_t phys_addr, pgprot_t prot)
 {
+	pgtbl_mod_mask mask = 0;
 	int err;
 
 	err = vmap_range_noflush(addr, end, phys_addr, pgprot_nx(prot),
-				 ioremap_max_page_shift);
+				 ioremap_max_page_shift, &mask);
+	if (mask & ARCH_PAGE_TABLE_SYNC_MASK)
+		arch_sync_kernel_mappings(addr, end);
+
 	flush_cache_vmap(addr, end);
 	if (!err)
 		err = kmsan_ioremap_page_range(addr, end, phys_addr, prot,
@@ -587,29 +585,24 @@ static int vmap_pages_p4d_range(pgd_t *pgd, unsigned long addr,
 }
 
 static int vmap_small_pages_range_noflush(unsigned long addr, unsigned long end,
-		pgprot_t prot, struct page **pages)
+		pgprot_t prot, struct page **pages, pgtbl_mod_mask *mask)
 {
-	unsigned long start = addr;
 	pgd_t *pgd;
 	unsigned long next;
 	int err = 0;
 	int nr = 0;
-	pgtbl_mod_mask mask = 0;
 
 	BUG_ON(addr >= end);
 	pgd = pgd_offset_k(addr);
 	do {
 		next = pgd_addr_end(addr, end);
 		if (pgd_bad(*pgd))
-			mask |= PGTBL_PGD_MODIFIED;
-		err = vmap_pages_p4d_range(pgd, addr, next, prot, pages, &nr, &mask);
+			*mask |= PGTBL_PGD_MODIFIED;
+		err = vmap_pages_p4d_range(pgd, addr, next, prot, pages, &nr, mask);
 		if (err)
 			break;
 	} while (pgd++, addr = next, addr != end);
 
-	if (mask & ARCH_PAGE_TABLE_SYNC_MASK)
-		arch_sync_kernel_mappings(start, end);
-
 	return err;
 }
 
@@ -626,26 +619,33 @@ int __vmap_pages_range_noflush(unsigned long addr, unsigned long end,
 		pgprot_t prot, struct page **pages, unsigned int page_shift)
 {
 	unsigned int i, nr = (end - addr) >> PAGE_SHIFT;
+	unsigned long start = addr;
+	pgtbl_mod_mask mask = 0;
+	int err = 0;
 
 	WARN_ON(page_shift < PAGE_SHIFT);
 
 	if (!IS_ENABLED(CONFIG_HAVE_ARCH_HUGE_VMALLOC) ||
-			page_shift == PAGE_SHIFT)
-		return vmap_small_pages_range_noflush(addr, end, prot, pages);
-
-	for (i = 0; i < nr; i += 1U << (page_shift - PAGE_SHIFT)) {
-		int err;
-
-		err = vmap_range_noflush(addr, addr + (1UL << page_shift),
-					page_to_phys(pages[i]), prot,
-					page_shift);
-		if (err)
-			return err;
+			page_shift == PAGE_SHIFT) {
+		err = vmap_small_pages_range_noflush(addr, end, prot, pages,
+						&mask);
+	} else {
+		for (i = 0; i < nr; i += 1U << (page_shift - PAGE_SHIFT)) {
+			err = vmap_range_noflush(addr,
+						addr + (1UL << page_shift),
+						page_to_phys(pages[i]), prot,
+						page_shift, &mask);
+			if (err)
+				break;
 
-		addr += 1UL << page_shift;
+			addr += 1UL << page_shift;
+		}
 	}
 
-	return 0;
+	if (mask & ARCH_PAGE_TABLE_SYNC_MASK)
+		arch_sync_kernel_mappings(start, end);
+
+	return err;
 }
 
 int vmap_pages_range_noflush(unsigned long addr, unsigned long end,
-- 
2.43.0