xen: use spin_lock_nest_lock when pinning a pagetable

When pinning/unpinning a pagetable with split pte locks, we can end up
holding multiple pte locks at once (we need to hold the locks while
there's a pending batched hypercall affecting the pte page).  Because
all the pte locks are in the same lock class, lockdep thinks that
we're potentially taking a lock recursively.

This warning is spurious because we always take the pte locks while
holding mm->page_table_lock.  lockdep now has spin_lock_nest_lock to
express this kind of dominant lock use, so use it here so that lockdep
knows what's going on.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 48 insertions, 26 deletions

diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c
index 64e58681767e..ae173f6edd8b 100644
--- a/arch/x86/xen/mmu.c
+++ b/arch/x86/xen/mmu.c
@@ -651,9 +651,12 @@ void xen_set_pgd(pgd_t *ptr, pgd_t val)
  * For 64-bit, we must skip the Xen hole in the middle of the address
  * space, just after the big x86-64 virtual hole.
  */
-static int xen_pgd_walk(pgd_t *pgd, int (*func)(struct page *, enum pt_level),
+static int xen_pgd_walk(struct mm_struct *mm,
+                        int (*func)(struct mm_struct *mm, struct page *,
+                                    enum pt_level),
                         unsigned long limit)
 {
+        pgd_t *pgd = mm->pgd;
         int flush = 0;
         unsigned hole_low, hole_high;
         unsigned pgdidx_limit, pudidx_limit, pmdidx_limit;
@@ -698,7 +701,7 @@ static int xen_pgd_walk(pgd_t *pgd, int (*func)(struct page *, enum pt_level),
                 pud = pud_offset(&pgd[pgdidx], 0);
 
                 if (PTRS_PER_PUD > 1) /* not folded */
-                        flush |= (*func)(virt_to_page(pud), PT_PUD);
+                        flush |= (*func)(mm, virt_to_page(pud), PT_PUD);
 
                 for (pudidx = 0; pudidx < PTRS_PER_PUD; pudidx++) {
                         pmd_t *pmd;
@@ -713,7 +716,7 @@ static int xen_pgd_walk(pgd_t *pgd, int (*func)(struct page *, enum pt_level),
                         pmd = pmd_offset(&pud[pudidx], 0);
 
                         if (PTRS_PER_PMD > 1) /* not folded */
-                                flush |= (*func)(virt_to_page(pmd), PT_PMD);
+                                flush |= (*func)(mm, virt_to_page(pmd), PT_PMD);
 
                         for (pmdidx = 0; pmdidx < PTRS_PER_PMD; pmdidx++) {
                                 struct page *pte;
@@ -727,7 +730,7 @@ static int xen_pgd_walk(pgd_t *pgd, int (*func)(struct page *, enum pt_level),
                                         continue;
 
                                 pte = pmd_page(pmd[pmdidx]);
-                                flush |= (*func)(pte, PT_PTE);
+                                flush |= (*func)(mm, pte, PT_PTE);
                         }
                 }
         }
@@ -735,20 +738,20 @@ static int xen_pgd_walk(pgd_t *pgd, int (*func)(struct page *, enum pt_level),
 out:
         /* Do the top level last, so that the callbacks can use it as
            a cue to do final things like tlb flushes. */
-        flush |= (*func)(virt_to_page(pgd), PT_PGD);
+        flush |= (*func)(mm, virt_to_page(pgd), PT_PGD);
 
         return flush;
 }
 
 /* If we're using split pte locks, then take the page's lock and
    return a pointer to it.  Otherwise return NULL. */
-static spinlock_t *xen_pte_lock(struct page *page)
+static spinlock_t *xen_pte_lock(struct page *page, struct mm_struct *mm)
 {
         spinlock_t *ptl = NULL;
 
 #if USE_SPLIT_PTLOCKS
         ptl = __pte_lockptr(page);
-        spin_lock(ptl);
+        spin_lock_nest_lock(ptl, &mm->page_table_lock);
 #endif
 
         return ptl;
@@ -772,7 +775,8 @@ static void xen_do_pin(unsigned level, unsigned long pfn)
         MULTI_mmuext_op(mcs.mc, op, 1, NULL, DOMID_SELF);
 }
 
-static int xen_pin_page(struct page *page, enum pt_level level)
+static int xen_pin_page(struct mm_struct *mm, struct page *page,
+                        enum pt_level level)
 {
         unsigned pgfl = TestSetPagePinned(page);
         int flush;
@@ -813,7 +817,7 @@ static int xen_pin_page(struct page *page, enum pt_level level)
                  */
                 ptl = NULL;
                 if (level == PT_PTE)
-                        ptl = xen_pte_lock(page);
+                        ptl = xen_pte_lock(page, mm);
 
                 MULTI_update_va_mapping(mcs.mc, (unsigned long)pt,
                                         pfn_pte(pfn, PAGE_KERNEL_RO),
@@ -834,11 +838,11 @@ static int xen_pin_page(struct page *page, enum pt_level level)
 /* This is called just after a mm has been created, but it has not
    been used yet.  We need to make sure that its pagetable is all
    read-only, and can be pinned. */
-void xen_pgd_pin(pgd_t *pgd)
+static void __xen_pgd_pin(struct mm_struct *mm, pgd_t *pgd)
 {
         xen_mc_batch();
 
-        if (xen_pgd_walk(pgd, xen_pin_page, USER_LIMIT)) {
+        if (xen_pgd_walk(mm, xen_pin_page, USER_LIMIT)) {
                 /* re-enable interrupts for kmap_flush_unused */
                 xen_mc_issue(0);
                 kmap_flush_unused();
@@ -852,25 +856,35 @@ void xen_pgd_pin(pgd_t *pgd)
                 xen_do_pin(MMUEXT_PIN_L4_TABLE, PFN_DOWN(__pa(pgd)));
 
                 if (user_pgd) {
-                        xen_pin_page(virt_to_page(user_pgd), PT_PGD);
+                        xen_pin_page(mm, virt_to_page(user_pgd), PT_PGD);
                         xen_do_pin(MMUEXT_PIN_L4_TABLE, PFN_DOWN(__pa(user_pgd)));
                 }
         }
 #else /* CONFIG_X86_32 */
 #ifdef CONFIG_X86_PAE
         /* Need to make sure unshared kernel PMD is pinnable */
-        xen_pin_page(virt_to_page(pgd_page(pgd[pgd_index(TASK_SIZE)])), PT_PMD);
+        xen_pin_page(mm, virt_to_page(pgd_page(pgd[pgd_index(TASK_SIZE)])),
+                     PT_PMD);
 #endif
         xen_do_pin(MMUEXT_PIN_L3_TABLE, PFN_DOWN(__pa(pgd)));
 #endif /* CONFIG_X86_64 */
         xen_mc_issue(0);
 }
 
+static void xen_pgd_pin(struct mm_struct *mm)
+{
+        __xen_pgd_pin(mm, mm->pgd);
+}
+
 /*
  * On save, we need to pin all pagetables to make sure they get their
  * mfns turned into pfns.  Search the list for any unpinned pgds and pin
  * them (unpinned pgds are not currently in use, probably because the
  * process is under construction or destruction).
+ *
+ * Expected to be called in stop_machine() ("equivalent to taking
+ * every spinlock in the system"), so the locking doesn't really
+ * matter all that much.
  */
 void xen_mm_pin_all(void)
 {
@@ -881,7 +895,7 @@ void xen_mm_pin_all(void)
 
         list_for_each_entry(page, &pgd_list, lru) {
                 if (!PagePinned(page)) {
-                        xen_pgd_pin((pgd_t *)page_address(page));
+                        __xen_pgd_pin(&init_mm, (pgd_t *)page_address(page));
                         SetPageSavePinned(page);
                 }
         }
@@ -894,7 +908,8 @@ void xen_mm_pin_all(void)
  * that's before we have page structures to store the bits.  So do all
  * the book-keeping now.
  */
-static __init int xen_mark_pinned(struct page *page, enum pt_level level)
+static __init int xen_mark_pinned(struct mm_struct *mm, struct page *page,
+                                  enum pt_level level)
 {
         SetPagePinned(page);
         return 0;
@@ -902,10 +917,11 @@ static __init int xen_mark_pinned(struct page *page, enum pt_level level)
 
 void __init xen_mark_init_mm_pinned(void)
 {
-        xen_pgd_walk(init_mm.pgd, xen_mark_pinned, FIXADDR_TOP);
+        xen_pgd_walk(&init_mm, xen_mark_pinned, FIXADDR_TOP);
 }
 
-static int xen_unpin_page(struct page *page, enum pt_level level)
+static int xen_unpin_page(struct mm_struct *mm, struct page *page,
+                          enum pt_level level)
 {
         unsigned pgfl = TestClearPagePinned(page);
 
@@ -923,7 +939,7 @@ static int xen_unpin_page(struct page *page, enum pt_level level)
                  * partially-pinned state.
                  */
                 if (level == PT_PTE) {
-                        ptl = xen_pte_lock(page);
+                        ptl = xen_pte_lock(page, mm);
 
                         if (ptl)
                                 xen_do_pin(MMUEXT_UNPIN_TABLE, pfn);
@@ -945,7 +961,7 @@ static int xen_unpin_page(struct page *page, enum pt_level level)
 }
 
 /* Release a pagetables pages back as normal RW */
-static void xen_pgd_unpin(pgd_t *pgd)
+static void __xen_pgd_unpin(struct mm_struct *mm, pgd_t *pgd)
 {
         xen_mc_batch();
 
@@ -957,21 +973,27 @@ static void xen_pgd_unpin(pgd_t *pgd)
 
                 if (user_pgd) {
                         xen_do_pin(MMUEXT_UNPIN_TABLE, PFN_DOWN(__pa(user_pgd)));
-                        xen_unpin_page(virt_to_page(user_pgd), PT_PGD);
+                        xen_unpin_page(mm, virt_to_page(user_pgd), PT_PGD);
                 }
         }
 #endif
 
 #ifdef CONFIG_X86_PAE
         /* Need to make sure unshared kernel PMD is unpinned */
-        xen_unpin_page(virt_to_page(pgd_page(pgd[pgd_index(TASK_SIZE)])), PT_PMD);
+        xen_unpin_page(mm, virt_to_page(pgd_page(pgd[pgd_index(TASK_SIZE)])),
+                       PT_PMD);
 #endif
 
-        xen_pgd_walk(pgd, xen_unpin_page, USER_LIMIT);
+        xen_pgd_walk(mm, xen_unpin_page, USER_LIMIT);
 
         xen_mc_issue(0);
 }
 
+static void xen_pgd_unpin(struct mm_struct *mm)
+{
+        __xen_pgd_unpin(mm, mm->pgd);
+}
+
 /*
  * On resume, undo any pinning done at save, so that the rest of the
  * kernel doesn't see any unexpected pinned pagetables.
@@ -986,7 +1008,7 @@ void xen_mm_unpin_all(void)
         list_for_each_entry(page, &pgd_list, lru) {
                 if (PageSavePinned(page)) {
                         BUG_ON(!PagePinned(page));
-                        xen_pgd_unpin((pgd_t *)page_address(page));
+                        __xen_pgd_unpin(&init_mm, (pgd_t *)page_address(page));
                         ClearPageSavePinned(page);
                 }
         }
@@ -997,14 +1019,14 @@ void xen_mm_unpin_all(void)
 void xen_activate_mm(struct mm_struct *prev, struct mm_struct *next)
 {
         spin_lock(&next->page_table_lock);
-        xen_pgd_pin(next->pgd);
+        xen_pgd_pin(next);
         spin_unlock(&next->page_table_lock);
 }
 
 void xen_dup_mmap(struct mm_struct *oldmm, struct mm_struct *mm)
 {
         spin_lock(&mm->page_table_lock);
-        xen_pgd_pin(mm->pgd);
+        xen_pgd_pin(mm);
         spin_unlock(&mm->page_table_lock);
 }
 
@@ -1095,7 +1117,7 @@ void xen_exit_mmap(struct mm_struct *mm)
 
         /* pgd may not be pinned in the error exit path of execve */
         if (xen_page_pinned(mm->pgd))
-                xen_pgd_unpin(mm->pgd);
+                xen_pgd_unpin(mm);
 
         spin_unlock(&mm->page_table_lock);
 }