[PATCH] xen: use spin_lock_nest_lock when pinning a pagetable

[Jeremy Fitzhardinge]

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@xxxxxxxxxx>
---
arch/x86/xen/mmu.c |   74 +++++++++++++++++++++++++++++++++-------------------
arch/x86/xen/mmu.h |    3 --
2 files changed, 48 insertions(+), 29 deletions(-)

===================================================================
--- a/arch/x86/xen/mmu.c
+++ b/arch/x86/xen/mmu.c
@@ -651,9 +651,12 @@
 * 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 @@
		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 @@
			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 @@
					continue;

				pte = pmd_page(pmd[pmdidx]);
-				flush |= (*func)(pte, PT_PTE);
+				flush |= (*func)(mm, pte, PT_PTE);
			}
		}
	}
@@ -735,20 +738,20 @@
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 @@
	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 @@
		 */
		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 @@
/* 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();
@@ -852,18 +856,24 @@
		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);
}

/*
@@ -871,6 +881,10 @@
 * 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 @@

	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 @@
 * 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 @@

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 @@
		 * 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 @@
}

/* 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();

@@ -957,19 +973,25 @@

		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);
}

/*
@@ -986,7 +1008,7 @@
	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_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 @@

	/* 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);
}
===================================================================
--- a/arch/x86/xen/mmu.h
+++ b/arch/x86/xen/mmu.h
@@ -17,9 +17,6 @@
void xen_activate_mm(struct mm_struct *prev, struct mm_struct *next);
void xen_dup_mmap(struct mm_struct *oldmm, struct mm_struct *mm);
void xen_exit_mmap(struct mm_struct *mm);
-
-void xen_pgd_pin(pgd_t *pgd);
-//void xen_pgd_unpin(pgd_t *pgd);

pteval_t xen_pte_val(pte_t);
pmdval_t xen_pmd_val(pmd_t);


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