[PATCH 07/12] x86/virt/guest/xen: Remove use of pgd_list from the Xen guest code

[Ingo Molnar <mingo@kernel.org>]

xen_mm_pin_all()/unpin_all() are used to implement full guest instance
suspend/restore. It's a stop-all method that needs to iterate through
all allocated pgds in the system to fix them up for Xen's use.

This code uses pgd_list, probably because it was an easy interface.

But we want to remove the pgd_list, so convert the code over to walk
all tasks in the system. This is an equivalent method.

(As I don't use Xen this is was only build tested.)

Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Waiman Long <Waiman.Long@hp.com>
Cc: linux-mm@kvack.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 arch/x86/xen/mmu.c | 51 ++++++++++++++++++++++++++++++++++++++-------------
 1 file changed, 38 insertions(+), 13 deletions(-)

diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c
index dd151b2045b0..70a3df5b0b54 100644
--- a/arch/x86/xen/mmu.c
+++ b/arch/x86/xen/mmu.c
@@ -853,15 +853,27 @@ static void xen_pgd_pin(struct mm_struct *mm)
  */
 void xen_mm_pin_all(void)
 {
-	struct page *page;
+	struct task_struct *g, *p;
 
-	spin_lock(&pgd_lock);
+	spin_lock(&pgd_lock); /* Implies rcu_read_lock() for the task list iteration: */
 
-	list_for_each_entry(page, &pgd_list, lru) {
-		if (!PagePinned(page)) {
-			__xen_pgd_pin(&init_mm, (pgd_t *)page_address(page));
-			SetPageSavePinned(page);
+	for_each_process_thread(g, p) {
+		struct mm_struct *mm;
+		struct page *page;
+		pgd_t *pgd;
+
+		task_lock(p);
+		mm = p->mm;
+		if (mm) {
+			pgd = mm->pgd;
+			page = virt_to_page(pgd);
+
+			if (!PagePinned(page)) {
+				__xen_pgd_pin(&init_mm, pgd);
+				SetPageSavePinned(page);
+			}
 		}
+		task_unlock(p);
 	}
 
 	spin_unlock(&pgd_lock);
@@ -967,19 +979,32 @@ static void xen_pgd_unpin(struct mm_struct *mm)
  */
 void xen_mm_unpin_all(void)
 {
-	struct page *page;
+	struct task_struct *g, *p;
 
-	spin_lock(&pgd_lock);
+	spin_lock(&pgd_lock); /* Implies rcu_read_lock() for the task list iteration: */
 
-	list_for_each_entry(page, &pgd_list, lru) {
-		if (PageSavePinned(page)) {
-			BUG_ON(!PagePinned(page));
-			__xen_pgd_unpin(&init_mm, (pgd_t *)page_address(page));
-			ClearPageSavePinned(page);
+	for_each_process_thread(g, p) {
+		struct mm_struct *mm;
+		struct page *page;
+		pgd_t *pgd;
+
+		task_lock(p);
+		mm = p->mm;
+		if (mm) {
+			pgd = mm->pgd;
+			page = virt_to_page(pgd);
+
+			if (PageSavePinned(page)) {
+				BUG_ON(!PagePinned(page));
+				__xen_pgd_unpin(&init_mm, pgd);
+				ClearPageSavePinned(page);
+			}
 		}
+		task_unlock(p);
 	}
 
 	spin_unlock(&pgd_lock);
+	rcu_read_unlock();
 }
 
 static void xen_activate_mm(struct mm_struct *prev, struct mm_struct *next)
-- 
2.1.4