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Subject[patch 05/18] remap_file_pages protection support: enhance syscall interface
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From: Ingo Molnar <mingo@elte.hu>, Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>

This contains simply the changes to the syscall code, based on Ingo's patch.
Differently from his one, I've *not* added a new syscall, choosing to add a
new flag (MAP_NOINHERIT) which the application must specify to get the new
behavior (prot != 0 is accepted and prot == 0 means PROT_NONE).

Enable the 'prot' parameter for shared-writable mappings (the ones which are
the primary target for remap_file_pages), without breaking up the vma.

*** remap_file_pages protection support: use EOVERFLOW ret code

Use -EOVERFLOW ("Value too large for defined data type") rather than -EINVAL
when we cannot store the file offset in the PTE.

Signed-off-by: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
---

linux-2.6.git-paolo/mm/fremap.c | 40 +++++++++++++++++++++++++++++++---------
1 files changed, 31 insertions(+), 9 deletions(-)

diff -puN mm/fremap.c~rfp-enhance-syscall mm/fremap.c
--- linux-2.6.git/mm/fremap.c~rfp-enhance-syscall 2005-08-24 20:55:35.000000000 +0200
+++ linux-2.6.git-paolo/mm/fremap.c 2005-08-24 20:56:49.000000000 +0200
@@ -4,6 +4,10 @@
* Explicit pagetable population and nonlinear (random) mappings support.
*
* started by Ingo Molnar, Copyright (C) 2002, 2003
+ *
+ * support of nonuniform remappings:
+ * Copyright (C) 2004 Ingo Molnar
+ * Copyright (C) 2005 Paolo 'Blaisorblade' Giarrusso
*/

#include <linux/mm.h>
@@ -164,18 +168,14 @@ err_unlock:
* file within an existing vma.
* @start: start of the remapped virtual memory range
* @size: size of the remapped virtual memory range
- * @prot: new protection bits of the range
+ * @prot: new protection bits of the range, must be 0 if not using MAP_NOINHERIT
* @pgoff: to be mapped page of the backing store file
- * @flags: 0 or MAP_NONBLOCKED - the later will cause no IO.
+ * @flags: bits MAP_NOINHERIT or MAP_NONBLOCKED - the later will cause no IO.
*
* this syscall works purely via pagetables, so it's the most efficient
* way to map the same (large) file into a given virtual window. Unlike
* mmap()/mremap() it does not create any new vmas. The new mappings are
* also safe across swapout.
- *
- * NOTE: the 'prot' parameter right now is ignored, and the vma's default
- * protection is used. Arbitrary protections might be implemented in the
- * future.
*/
asmlinkage long sys_remap_file_pages(unsigned long start, unsigned long size,
unsigned long prot, unsigned long pgoff, unsigned long flags)
@@ -188,7 +188,7 @@ asmlinkage long sys_remap_file_pages(uns
int has_write_lock = 0;
pgprot_t pgprot;

- if (prot)
+ if (prot && !(flags & MAP_NOINHERIT))
goto out;
/*
* Sanitize the syscall parameters:
@@ -203,7 +203,7 @@ asmlinkage long sys_remap_file_pages(uns
/* Can we represent this offset inside this architecture's pte's? */
#if PTE_FILE_MAX_BITS < BITS_PER_LONG
if (pgoff + (size >> PAGE_SHIFT) >= (1UL << PTE_FILE_MAX_BITS))
- return err;
+ return -EOVERFLOW;
#endif

/* We need down_write() to change vma->vm_flags. */
@@ -228,7 +228,18 @@ retry:
vma->vm_start || end > vma->vm_end)
goto out_unlock;

- pgprot = vma->vm_page_prot;
+ if (flags & MAP_NOINHERIT) {
+ err = -EPERM;
+ if (((prot & PROT_READ) && !(vma->vm_flags & VM_MAYREAD)))
+ goto out_unlock;
+ if (((prot & PROT_WRITE) && !(vma->vm_flags & VM_MAYWRITE)))
+ goto out_unlock;
+ if (((prot & PROT_EXEC) && !(vma->vm_flags & VM_MAYEXEC)))
+ goto out_unlock;
+ err = -EINVAL;
+ pgprot = protection_map[calc_vm_prot_bits(prot) | VM_SHARED];
+ } else
+ pgprot = vma->vm_page_prot;

if (!vma->vm_private_data ||
(vma->vm_flags & (VM_NONLINEAR|VM_RESERVED))) {
@@ -251,6 +262,17 @@ retry:
spin_unlock(&mapping->i_mmap_lock);
}

+ if (pgprot_val(pgprot) != pgprot_val(vma->vm_page_prot) &&
+ !(vma->vm_flags & VM_NONUNIFORM)) {
+ if (!has_write_lock) {
+ up_read(&mm->mmap_sem);
+ down_write(&mm->mmap_sem);
+ has_write_lock = 1;
+ goto retry;
+ }
+ vma->vm_flags |= VM_NONUNIFORM;
+ }
+
/* Do NOT hold the write lock while doing any I/O, nor when
* iterating over too many PTEs. Values might need tuning. */
if (has_write_lock && (!(flags & MAP_NONBLOCK) || size > INSTALL_SIZE)) {
_
-
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