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Subject[PATCH 1/2] mm: Allow arch code to control the user page table ceiling
Date
From: Hugh Dickins <hughd@google.com>

On architectures where a pgd entry may be shared between user and kernel
(ARM+LPAE), freeing page tables needs a ceiling other than 0. This patch
introduces a generic USER_PGTABLES_CEILING that arch code can override.

Signed-off-by: Hugh Dickins <hughd@google.com>
[catalin.marinas@arm.com: commit log; shift_arg_pages(), asm-generic/pgtables.h changes]
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: Andrew Morton <akpm@linux-foundation.org>
---
fs/exec.c | 4 ++--
include/asm-generic/pgtable.h | 10 ++++++++++
mm/mmap.c | 4 ++--
3 files changed, 14 insertions(+), 4 deletions(-)

diff --git a/fs/exec.c b/fs/exec.c
index 20df02c..547eaaa 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -613,7 +613,7 @@ static int shift_arg_pages(struct vm_area_struct *vma, unsigned long shift)
* when the old and new regions overlap clear from new_end.
*/
free_pgd_range(&tlb, new_end, old_end, new_end,
- vma->vm_next ? vma->vm_next->vm_start : 0);
+ vma->vm_next ? vma->vm_next->vm_start : USER_PGTABLES_CEILING);
} else {
/*
* otherwise, clean from old_start; this is done to not touch
@@ -622,7 +622,7 @@ static int shift_arg_pages(struct vm_area_struct *vma, unsigned long shift)
* for the others its just a little faster.
*/
free_pgd_range(&tlb, old_start, old_end, new_end,
- vma->vm_next ? vma->vm_next->vm_start : 0);
+ vma->vm_next ? vma->vm_next->vm_start : USER_PGTABLES_CEILING);
}
tlb_finish_mmu(&tlb, new_end, old_end);

diff --git a/include/asm-generic/pgtable.h b/include/asm-generic/pgtable.h
index 5cf680a..f50a87d 100644
--- a/include/asm-generic/pgtable.h
+++ b/include/asm-generic/pgtable.h
@@ -7,6 +7,16 @@
#include <linux/mm_types.h>
#include <linux/bug.h>

+/*
+ * On almost all architectures and configurations, 0 can be used as the
+ * upper ceiling to free_pgtables(): on many architectures it has the same
+ * effect as using TASK_SIZE. However, there is one configuration which
+ * must impose a more careful limit, to avoid freeing kernel pgtables.
+ */
+#ifndef USER_PGTABLES_CEILING
+#define USER_PGTABLES_CEILING 0UL
+#endif
+
#ifndef __HAVE_ARCH_PTEP_SET_ACCESS_FLAGS
extern int ptep_set_access_flags(struct vm_area_struct *vma,
unsigned long address, pte_t *ptep,
diff --git a/mm/mmap.c b/mm/mmap.c
index d1e4124..e262710 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2262,7 +2262,7 @@ static void unmap_region(struct mm_struct *mm,
update_hiwater_rss(mm);
unmap_vmas(&tlb, vma, start, end);
free_pgtables(&tlb, vma, prev ? prev->vm_end : FIRST_USER_ADDRESS,
- next ? next->vm_start : 0);
+ next ? next->vm_start : USER_PGTABLES_CEILING);
tlb_finish_mmu(&tlb, start, end);
}

@@ -2640,7 +2640,7 @@ void exit_mmap(struct mm_struct *mm)
/* Use -1 here to ensure all VMAs in the mm are unmapped */
unmap_vmas(&tlb, vma, 0, -1);

- free_pgtables(&tlb, vma, FIRST_USER_ADDRESS, 0);
+ free_pgtables(&tlb, vma, FIRST_USER_ADDRESS, USER_PGTABLES_CEILING);
tlb_finish_mmu(&tlb, 0, -1);

/*

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