From b6174df5eec9cdfd598c03d6d0807e344e109213 Mon Sep 17 00:00:00 2001 From: "Zhang, Yanmin" Date: Mon, 10 Jul 2006 04:44:49 -0700 Subject: [PATCH] [PATCH] mmap zero-length hugetlb file with PROT_NONE to protect a hugetlb virtual area Sometimes, applications need below call to be successful although "/mnt/hugepages/file1" doesn't exist. fd = open("/mnt/hugepages/file1", O_CREAT|O_RDWR, 0755); *addr = mmap(NULL, 0x1024*1024*256, PROT_NONE, 0, fd, 0); As for regular pages (or files), above call does work, but as for huge pages, above call would fail because hugetlbfs_file_mmap would fail if (!(vma->vm_flags & VM_WRITE) && len > inode->i_size). This capability on huge page is useful on ia64 when the process wants to protect one area on region 4, so other threads couldn't read/write this area. A famous JVM (Java Virtual Machine) implementation on IA64 needs the capability. Signed-off-by: Zhang Yanmin Cc: David Gibson Cc: Hugh Dickins [ Expand-on-mmap semantics again... this time matching normal fs's. wli ] Acked-by: William Lee Irwin III Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- fs/hugetlbfs/inode.c | 4 +--- 1 file changed, 1 insertion(+), 3 deletions(-) diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c index 6449cb697967..c3920c96dadf 100644 --- a/fs/hugetlbfs/inode.c +++ b/fs/hugetlbfs/inode.c @@ -83,8 +83,6 @@ static int hugetlbfs_file_mmap(struct file *file, struct vm_area_struct *vma) ret = -ENOMEM; len = vma_len + ((loff_t)vma->vm_pgoff << PAGE_SHIFT); - if (!(vma->vm_flags & VM_WRITE) && len > inode->i_size) - goto out; if (vma->vm_flags & VM_MAYSHARE && hugetlb_reserve_pages(inode, vma->vm_pgoff >> (HPAGE_SHIFT-PAGE_SHIFT), @@ -93,7 +91,7 @@ static int hugetlbfs_file_mmap(struct file *file, struct vm_area_struct *vma) ret = 0; hugetlb_prefault_arch_hook(vma->vm_mm); - if (inode->i_size < len) + if (vma->vm_flags & VM_WRITE && inode->i_size < len) inode->i_size = len; out: mutex_unlock(&inode->i_mutex); -- 2.39.5