linux-kernel - [PATCH v2 15/15] mm/mmap: Move may_expand_vm() check in mmap

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Date: Tue, 25 Jun 2024 15:11:45 -0400
From: "Liam R. Howlett" <Liam.Howlett@...cle.com>
To: linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>
Cc: Suren Baghdasaryan <surenb@...gle.com>, Vlastimil Babka <vbabka@...e.cz>,
        Lorenzo Stoakes <lstoakes@...il.com>,
        Matthew Wilcox <willy@...radead.org>, sidhartha.kumar@...cle.com,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Bert Karwatzki <spasswolf@....de>, Jiri Olsa <olsajiri@...il.com>,
        linux-kernel@...r.kernel.org, Kees Cook <kees@...nel.org>,
        "Liam R. Howlett" <Liam.Howlett@...cle.com>
Subject: [PATCH v2 15/15] mm/mmap: Move may_expand_vm() check in mmap_region()

From: "Liam R. Howlett" <Liam.Howlett@...cle.com>

The MAP_FIXED page count is available after the vms_gather_munmap_vmas()
call, so use it instead of looping over the vmas twice.

Signed-off-by: Liam R. Howlett <Liam.Howlett@...cle.com>
---
 mm/mmap.c | 36 ++++--------------------------------
 1 file changed, 4 insertions(+), 32 deletions(-)

diff --git a/mm/mmap.c b/mm/mmap.c
index adb0bb5ea344..a310b05a01c2 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -405,27 +405,6 @@ anon_vma_interval_tree_post_update_vma(struct vm_area_struct *vma)
 		anon_vma_interval_tree_insert(avc, &avc->anon_vma->rb_root);
 }
 
-static unsigned long count_vma_pages_range(struct mm_struct *mm,
-		unsigned long addr, unsigned long end,
-		unsigned long *nr_accounted)
-{
-	VMA_ITERATOR(vmi, mm, addr);
-	struct vm_area_struct *vma;
-	unsigned long nr_pages = 0;
-
-	*nr_accounted = 0;
-	for_each_vma_range(vmi, vma, end) {
-		unsigned long vm_start = max(addr, vma->vm_start);
-		unsigned long vm_end = min(end, vma->vm_end);
-
-		nr_pages += PHYS_PFN(vm_end - vm_start);
-		if (vma->vm_flags & VM_ACCOUNT)
-			*nr_accounted += PHYS_PFN(vm_end - vm_start);
-	}
-
-	return nr_pages;
-}
-
 static void __vma_link_file(struct vm_area_struct *vma,
 			    struct address_space *mapping)
 {
@@ -2936,17 +2915,6 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
 	pgoff_t vm_pgoff;
 	int error = -ENOMEM;
 	VMA_ITERATOR(vmi, mm, addr);
-	unsigned long nr_pages, nr_accounted;
-
-	nr_pages = count_vma_pages_range(mm, addr, end, &nr_accounted);
-
-	/* Check against address space limit. */
-	/*
-	 * MAP_FIXED may remove pages of mappings that intersects with requested
-	 * mapping. Account for the pages it would unmap.
-	 */
-	if (!may_expand_vm(mm, vm_flags, pglen - nr_pages))
-		return -ENOMEM;
 
 	if (unlikely(!can_modify_mm(mm, addr, end)))
 		return -EPERM;
@@ -2977,6 +2945,10 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
 			vma_iter_next_range(&vmi);
 	}
 
+	/* Check against address space limit. */
+	if (!may_expand_vm(mm, vm_flags, pglen - vms.nr_pages))
+		goto abort_munmap;
+
 	/*
 	 * Private writable mapping: check memory availability
 	 */
-- 
2.43.0