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Date:   Fri, 6 Dec 2019 16:37:07 -0800
From:   Andrew Morton <akpm@linux-foundation.org>
To:     Daniel Axtens <dja@axtens.net>
Cc:     kasan-dev@googlegroups.com, linux-mm@kvack.org,
        aryabinin@virtuozzo.com, glider@google.com,
        linux-kernel@vger.kernel.org, dvyukov@google.com,
        daniel@iogearbox.net, cai@lca.pw
Subject: Re: [PATCH 1/3] mm: add apply_to_existing_pages helper
Message-Id: <20191206163707.17f627c502846bd636049ad4@linux-foundation.org>
In-Reply-To: <20191205140407.1874-1-dja@axtens.net>
References: <20191205140407.1874-1-dja@axtens.net>
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On Fri,  6 Dec 2019 01:04:05 +1100 Daniel Axtens <dja@axtens.net> wrote:

> +/*
> + * Scan a region of virtual memory, calling a provided function on
> + * each leaf page table where it exists.
> + *
> + * Unlike apply_to_page_range, this does _not_ fill in page tables
> + * where they are absent.
> + */
> +int apply_to_existing_pages(struct mm_struct *mm, unsigned long addr,
> +			    unsigned long size, pte_fn_t fn, void *data)
> +{
> +	pgd_t *pgd;
> +	unsigned long next;
> +	unsigned long end = addr + size;
> +	int err = 0;
> +
> +	if (WARN_ON(addr >= end))
> +		return -EINVAL;
> +
> +	pgd = pgd_offset(mm, addr);
> +	do {
> +		next = pgd_addr_end(addr, end);
> +		if (pgd_none_or_clear_bad(pgd))
> +			continue;
> +		err = apply_to_p4d_range(mm, pgd, addr, next, fn, data, false);
> +		if (err)
> +			break;
> +	} while (pgd++, addr = next, addr != end);
> +
> +	return err;
> +}
> +EXPORT_SYMBOL_GPL(apply_to_existing_pages);

This is almost identical to apply_to_page_range() and cries out for
some deduplication.  This?

--- a/mm/memory.c~mm-add-apply_to_existing_pages-helper-fix
+++ a/mm/memory.c
@@ -2141,12 +2141,9 @@ static int apply_to_p4d_range(struct mm_
 	return err;
 }
 
-/*
- * Scan a region of virtual memory, filling in page tables as necessary
- * and calling a provided function on each leaf page table.
- */
-int apply_to_page_range(struct mm_struct *mm, unsigned long addr,
-			unsigned long size, pte_fn_t fn, void *data)
+static int __apply_to_page_range(struct mm_struct *mm, unsigned long addr,
+				 unsigned long size, pte_fn_t fn,
+				 void *data, bool create)
 {
 	pgd_t *pgd;
 	unsigned long next;
@@ -2159,13 +2156,25 @@ int apply_to_page_range(struct mm_struct
 	pgd = pgd_offset(mm, addr);
 	do {
 		next = pgd_addr_end(addr, end);
-		err = apply_to_p4d_range(mm, pgd, addr, next, fn, data, true);
+		if (!create && pgd_none_or_clear_bad(pgd))
+			continue;
+		err = apply_to_p4d_range(mm, pgd, addr, next, fn, data, create);
 		if (err)
 			break;
 	} while (pgd++, addr = next, addr != end);
 
 	return err;
 }
+
+/*
+ * Scan a region of virtual memory, filling in page tables as necessary
+ * and calling a provided function on each leaf page table.
+ */
+int apply_to_page_range(struct mm_struct *mm, unsigned long addr,
+			unsigned long size, pte_fn_t fn, void *data)
+{
+	return __apply_to_page_range(mm, addr, size, fn, data, true);
+}
 EXPORT_SYMBOL_GPL(apply_to_page_range);
 
 /*
@@ -2178,25 +2187,7 @@ EXPORT_SYMBOL_GPL(apply_to_page_range);
 int apply_to_existing_pages(struct mm_struct *mm, unsigned long addr,
 			    unsigned long size, pte_fn_t fn, void *data)
 {
-	pgd_t *pgd;
-	unsigned long next;
-	unsigned long end = addr + size;
-	int err = 0;
-
-	if (WARN_ON(addr >= end))
-		return -EINVAL;
-
-	pgd = pgd_offset(mm, addr);
-	do {
-		next = pgd_addr_end(addr, end);
-		if (pgd_none_or_clear_bad(pgd))
-			continue;
-		err = apply_to_p4d_range(mm, pgd, addr, next, fn, data, false);
-		if (err)
-			break;
-	} while (pgd++, addr = next, addr != end);
-
-	return err;
+	return __apply_to_page_range(mm, addr, size, fn, data, false);
 }
 EXPORT_SYMBOL_GPL(apply_to_existing_pages);
 
_