[patch 1/3] [PATCH] mm: migration -- Do not loose soft dirty bit if page is in migration state

[Cyrill Gorcunov <gorcunov@gmail.com>]

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If page migration is turne on in the config and the page is migrating,
we may loose soft dirty bit. If fork and mprotect if called on migrating
pages (once migration is complete) pages do not obtain soft dirty bit
in correspond pte entries. Fix it adding appropriate test on swap
entries.

Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Cc: Pavel Emelyanov <xemul@parallels.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Matt Mackall <mpm@selenic.com>
Cc: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@gmail.com>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
---
 mm/memory.c   |    2 ++
 mm/migrate.c  |    2 ++
 mm/mprotect.c |    7 +++++--
 3 files changed, 9 insertions(+), 2 deletions(-)

Index: linux-2.6.git/mm/memory.c
===================================================================
--- linux-2.6.git.orig/mm/memory.c
+++ linux-2.6.git/mm/memory.c
@@ -837,6 +837,8 @@ copy_one_pte(struct mm_struct *dst_mm, s
 					 */
 					make_migration_entry_read(&entry);
 					pte = swp_entry_to_pte(entry);
+					if (pte_swp_soft_dirty(*src_pte))
+						pte = pte_swp_mksoft_dirty(pte);
 					set_pte_at(src_mm, addr, src_pte, pte);
 				}
 			}
Index: linux-2.6.git/mm/migrate.c
===================================================================
--- linux-2.6.git.orig/mm/migrate.c
+++ linux-2.6.git/mm/migrate.c
@@ -161,6 +161,8 @@ static int remove_migration_pte(struct p
 
 	get_page(new);
 	pte = pte_mkold(mk_pte(new, vma->vm_page_prot));
+	if (pte_swp_soft_dirty(*ptep))
+		pte = pte_mksoft_dirty(pte);
 	if (is_write_migration_entry(entry))
 		pte = pte_mkwrite(pte);
 #ifdef CONFIG_HUGETLB_PAGE
Index: linux-2.6.git/mm/mprotect.c
===================================================================
--- linux-2.6.git.orig/mm/mprotect.c
+++ linux-2.6.git/mm/mprotect.c
@@ -94,13 +94,16 @@ static unsigned long change_pte_range(st
 			swp_entry_t entry = pte_to_swp_entry(oldpte);
 
 			if (is_write_migration_entry(entry)) {
+				pte_t newpte;
 				/*
 				 * A protection check is difficult so
 				 * just be safe and disable write
 				 */
 				make_migration_entry_read(&entry);
-				set_pte_at(mm, addr, pte,
-					swp_entry_to_pte(entry));
+				newpte = swp_entry_to_pte(entry);
+				if (pte_swp_soft_dirty(oldpte))
+					newpte = pte_swp_mksoft_dirty(newpte);
+				set_pte_at(mm, addr, pte, newpte);
 			}
 			pages++;
 		}

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