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FAILED: patch "[PATCH] mm: khugepaged: skip huge page collapse for special files" failed to apply to 5.10-stable tree

PATCH [email protected] 1 participant 1 message Oct 30, 2021

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Stable branch Memory management THP
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The patch below does not apply to the 5.10-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From a4aeaa06d45e90f9b279f0b09de84bd00006e733 Mon Sep 17 00:00:00 2001
From: Yang Shi <[email protected]>
Date: Thu, 28 Oct 2021 14:36:30 -0700
Subject: [PATCH] mm: khugepaged: skip huge page collapse for special files

The read-only THP for filesystems will collapse THP for files opened readonly and mapped with VM_EXEC. The intended usecase is to avoid TLB misses for large text segments. But it doesn't restrict the file types so a THP could be collapsed for a non-regular file, for example, block device, if it is opened readonly and mapped with EXEC permission. This may cause bugs, like [1] and [2].

This is definitely not the intended usecase, so just collapse THP for regular files in order to close the attack surface.

[[email protected]: fix vm_file check [3]]

Link https://lore.kernel.org/lkml/CACkBjsYwLYLRmX8GpsDpMthagWOjWWrNxqY6ZLNQVr6yx+f5vA@mail.gmail.com/ [1] open here
Link https://lore.kernel.org/linux-mm/[email protected]/ [2] open here
Link https://lkml.kernel.org/r/CAHbLzkqTW9U3VvTu1Ki5v_cLRC9gHW+znBukg_ycergE0JWj-A@mail.gmail.com [3] open here
Link https://lkml.kernel.org/r/[email protected] open here
Fixes 99cb0dbd47a1 ("mm,thp: add read-only THP support for (non-shmem) FS")
Signed-off-by Hugh Dickins <[email protected]>
Signed-off-by Yang Shi <[email protected]>
Reported-by Hao Sun <[email protected]>
Reported-by [email protected]
Cc Matthew Wilcox <[email protected]>
Cc Kirill A. Shutemov <[email protected]>
Cc Song Liu <[email protected]>
Cc Andrea Righi <[email protected]>
Cc <[email protected]>
Signed-off-by Andrew Morton <[email protected]>
Signed-off-by Linus Torvalds <[email protected]>
mm/khugepaged.c +11 -8
index 48de4e1b0783..8a8b3aa92937 100644
@@ -445,22 +445,25 @@ static bool hugepage_vma_check(struct vm_area_struct *vma,
 	if (!transhuge_vma_enabled(vma, vm_flags))
 		return false;
 
+	if (vma->vm_file && !IS_ALIGNED((vma->vm_start >> PAGE_SHIFT) -
+				vma->vm_pgoff, HPAGE_PMD_NR))
+		return false;
+
 	/* Enabled via shmem mount options or sysfs settings. */
-	if (shmem_file(vma->vm_file) && shmem_huge_enabled(vma)) {
-		return IS_ALIGNED((vma->vm_start >> PAGE_SHIFT) - vma->vm_pgoff,
-				HPAGE_PMD_NR);
-	}
+	if (shmem_file(vma->vm_file))
+		return shmem_huge_enabled(vma);
 
 	/* THP settings require madvise. */
 	if (!(vm_flags & VM_HUGEPAGE) && !khugepaged_always())
 		return false;
 
-	/* Read-only file mappings need to be aligned for THP to work. */
+	/* Only regular file is valid */
 	if (IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) && vma->vm_file &&
-	    !inode_is_open_for_write(vma->vm_file->f_inode) &&
 	    (vm_flags & VM_EXEC)) {
-		return IS_ALIGNED((vma->vm_start >> PAGE_SHIFT) - vma->vm_pgoff,
-				HPAGE_PMD_NR);
+		struct inode *inode = vma->vm_file->f_inode;
+
+		return !inode_is_open_for_write(inode) &&
+			S_ISREG(inode->i_mode);
 	}
 
 	if (!vma->anon_vma || vma->vm_ops)