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hugetlb: follow_hugetlb_page for write access

PATCH In review Adam Litke 3 participants 3 messages Nov 7, 2007 – Nov 19, 2007

Subsystems (3)
Memory management MM core HugeTLB
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Share & tools
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Adam Litke

author
#0 lore raw

PATCH 1/1 hugetlb: follow_hugetlb_page for write access

When calling get_user_pages(), a write flag is passed in by the caller to indicate if write access is required on the faulted-in pages. Currently, follow_hugetlb_page() ignores this flag and always faults pages for read-only access. This can cause data corruption because a device driver that calls get_user_pages() with write set will not expect COW faults to occur on the returned pages.

This patch passes the write flag down to follow_hugetlb_page() and makes sure hugetlb_fault() is called with the right write_access parameter.

Signed-off-by Adam Litke <[email protected]>

---

 include/linux/hugetlb.h |    2 +-
 mm/hugetlb.c            |    5 +++--
 mm/memory.c             |    2 +-
 3 files changed, 5 insertions(+), 4 deletions(-)
include/linux/hugetlb.h +1 -1
index 3a19b03..31fa0a0 100644
@@ -19,7 +19,7 @@ static inline int is_vm_hugetlb_page(struct vm_area_struct *vma)
 int hugetlb_sysctl_handler(struct ctl_table *, int, struct file *, void __user *, size_t *, loff_t *);
 int hugetlb_treat_movable_handler(struct ctl_table *, int, struct file *, void __user *, size_t *, loff_t *);
 int copy_hugetlb_page_range(struct mm_struct *, struct mm_struct *, struct vm_area_struct *);
-int follow_hugetlb_page(struct mm_struct *, struct vm_area_struct *, struct page **, struct vm_area_struct **, unsigned long *, int *, int);
+int follow_hugetlb_page(struct mm_struct *, struct vm_area_struct *, struct page **, struct vm_area_struct **, unsigned long *, int *, int, int);
 void unmap_hugepage_range(struct vm_area_struct *, unsigned long, unsigned long);
 void __unmap_hugepage_range(struct vm_area_struct *, unsigned long, unsigned long);
 int hugetlb_prefault(struct address_space *, struct vm_area_struct *);
mm/hugetlb.c +3 -2
index eab8c42..b645985 100644
@@ -621,7 +621,8 @@ int hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma,
 
 int follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
 			struct page **pages, struct vm_area_struct **vmas,
-			unsigned long *position, int *length, int i)
+			unsigned long *position, int *length, int i,
+			int write)
 {
 	unsigned long pfn_offset;
 	unsigned long vaddr = *position;

@@ -643,7 +644,7 @@ int follow_hugetlb_page(struct mm_struct *mm, struct vm_area_struct *vma,
 			int ret;
 
 			spin_unlock(&mm->page_table_lock);
-			ret = hugetlb_fault(mm, vma, vaddr, 0);
+			ret = hugetlb_fault(mm, vma, vaddr, write);
 			spin_lock(&mm->page_table_lock);
 			if (!(ret & VM_FAULT_ERROR))
 				continue;
mm/memory.c +1 -1
index f82b359..1bcd444 100644
@@ -1039,7 +1039,7 @@ int get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
 
 		if (is_vm_hugetlb_page(vma)) {
 			i = follow_hugetlb_page(mm, vma, pages, vmas,
-						&start, &len, i);
+						&start, &len, i, write);
 			continue;
 		}
Reviewed-by on v1 1/1
#1 lore raw
Quoted 11 lines · Adam Litke

When calling get_user_pages(), a write flag is passed in by the caller to indicate if write access is required on the faulted-in pages. Currently, follow_hugetlb_page() ignores this flag and always faults pages for read-only access. This can cause data corruption because a device driver that calls get_user_pages() with write set will not expect COW faults to occur on the returned pages.

This patch passes the write flag down to follow_hugetlb_page() and makes sure hugetlb_fault() is called with the right write_access parameter.

Signed-off-by Adam Litke <[email protected]>

Adam, this looks good.

Reviewed-by Ken Chen <[email protected]>
#2 lore raw
In reply to Adam Litke
Quoted 8 lines · Adam Litke

When calling get_user_pages(), a write flag is passed in by the caller to indicate if write access is required on the faulted-in pages. Currently, follow_hugetlb_page() ignores this flag and always faults pages for read-only access. This can cause data corruption because a device driver that calls get_user_pages() with write set will not expect COW faults to occur on the returned pages.

Quoted 4 lines

This patch passes the write flag down to follow_hugetlb_page() and makes sure hugetlb_fault() is called with the right write_access parameter.

Signed-off-by Adam Litke <[email protected]>

Apologize for this late response.
Tested on 2.6.23 with ehca and mthca. It works like a charm for me. Thanks!
Nam