[Xen-devel] [PATCH 3 of 5] Enforce ordering constraints for the page alloc lock in the PoD code

[Andres Lagar-Cavilla <andres@xxxxxxxxxxxxxxxx>]

 xen/arch/x86/mm/mm-locks.h   |  12 ++++++++++++
 xen/arch/x86/mm/p2m-pod.c    |  40 +++++++++++++++++++++++++++-------------
 xen/include/asm-x86/domain.h |   3 +++
 xen/include/asm-x86/p2m.h    |   5 +++++
 4 files changed, 47 insertions(+), 13 deletions(-)


The page alloc lock is sometimes used in the PoD code, with an
explicit expectation of ordering. Use our ordering constructs in the
mm layer to enforce this.

The additional book-keeping variables are kept in the arch_domain
sub-struct, as they are x86-specific to the whole domain.

Signed-off-by: Andres Lagar-Cavilla <andres@xxxxxxxxxxxxxxxx>

diff -r 81eedccb3a85 -r 0e8fb21ab4ff xen/arch/x86/mm/mm-locks.h
--- a/xen/arch/x86/mm/mm-locks.h
+++ b/xen/arch/x86/mm/mm-locks.h
@@ -174,6 +174,18 @@ declare_mm_lock(p2m)
 #define p2m_unlock(p)         mm_unlock(&(p)->lock)
 #define p2m_locked_by_me(p)   mm_locked_by_me(&(p)->lock)
 
+/* Page alloc lock (per-domain)
+ *
+ * This is an external lock, not represented by an mm_lock_t. However, 
+ * pod code uses it in conjunction with the p2m lock, and expecting
+ * the ordering which we enforce here.
+ * The lock is not recursive. */
+
+declare_mm_order_constraint(page_alloc)
+#define page_alloc_mm_pre_lock()   mm_enforce_order_lock_pre_page_alloc()
+#define page_alloc_mm_post_lock(l) mm_enforce_order_lock_post_page_alloc(&(l), 
NULL)
+#define page_alloc_mm_unlock(l)    mm_enforce_order_unlock((l), NULL)
+
 /* Paging lock (per-domain)
  *
  * For shadow pagetables, this lock protects
diff -r 81eedccb3a85 -r 0e8fb21ab4ff xen/arch/x86/mm/p2m-pod.c
--- a/xen/arch/x86/mm/p2m-pod.c
+++ b/xen/arch/x86/mm/p2m-pod.c
@@ -45,6 +45,20 @@
 
 #define superpage_aligned(_x)  (((_x)&(SUPERPAGE_PAGES-1))==0)
 
+/* Enforce lock ordering when grabbing the "external" page_alloc lock */
+static inline void lock_page_alloc(struct p2m_domain *p2m)
+{
+    page_alloc_mm_pre_lock();
+    spin_lock(&(p2m->domain->page_alloc_lock));
+    page_alloc_mm_post_lock(p2m->domain->arch.page_alloc_unlock_level);
+}
+
+static inline void unlock_page_alloc(struct p2m_domain *p2m)
+{
+    page_alloc_mm_unlock(p2m->domain->arch.page_alloc_unlock_level);
+    spin_unlock(&(p2m->domain->page_alloc_lock));
+}
+
 /*
  * Populate-on-demand functionality
  */
@@ -100,7 +114,7 @@ p2m_pod_cache_add(struct p2m_domain *p2m
         unmap_domain_page(b);
     }
 
-    spin_lock(&d->page_alloc_lock);
+    lock_page_alloc(p2m);
 
     /* First, take all pages off the domain list */
     for(i=0; i < 1 << order ; i++)
@@ -128,7 +142,7 @@ p2m_pod_cache_add(struct p2m_domain *p2m
      * This may cause "zombie domains" since the page will never be freed. */
     BUG_ON( d->arch.relmem != RELMEM_not_started );
 
-    spin_unlock(&d->page_alloc_lock);
+    unlock_page_alloc(p2m);
 
     return 0;
 }
@@ -245,7 +259,7 @@ p2m_pod_set_cache_target(struct p2m_doma
 
         /* Grab the lock before checking that pod.super is empty, or the last
          * entries may disappear before we grab the lock. */
-        spin_lock(&d->page_alloc_lock);
+        lock_page_alloc(p2m);
 
         if ( (p2m->pod.count - pod_target) > SUPERPAGE_PAGES
              && !page_list_empty(&p2m->pod.super) )
@@ -257,7 +271,7 @@ p2m_pod_set_cache_target(struct p2m_doma
 
         ASSERT(page != NULL);
 
-        spin_unlock(&d->page_alloc_lock);
+        unlock_page_alloc(p2m);
 
         /* Then free them */
         for ( i = 0 ; i < (1 << order) ; i++ )
@@ -378,7 +392,7 @@ p2m_pod_empty_cache(struct domain *d)
     BUG_ON(!d->is_dying);
     spin_barrier(&p2m->lock.lock);
 
-    spin_lock(&d->page_alloc_lock);
+    lock_page_alloc(p2m);
 
     while ( (page = page_list_remove_head(&p2m->pod.super)) )
     {
@@ -403,7 +417,7 @@ p2m_pod_empty_cache(struct domain *d)
 
     BUG_ON(p2m->pod.count != 0);
 
-    spin_unlock(&d->page_alloc_lock);
+    unlock_page_alloc(p2m);
 }
 
 int
@@ -417,7 +431,7 @@ p2m_pod_offline_or_broken_hit(struct pag
     if ( !(d = page_get_owner(p)) || !(p2m = p2m_get_hostp2m(d)) )
         return 0;
 
-    spin_lock(&d->page_alloc_lock);
+    lock_page_alloc(p2m);
     bmfn = mfn_x(page_to_mfn(p));
     page_list_for_each_safe(q, tmp, &p2m->pod.super)
     {
@@ -448,12 +462,12 @@ p2m_pod_offline_or_broken_hit(struct pag
         }
     }
 
-    spin_unlock(&d->page_alloc_lock);
+    unlock_page_alloc(p2m);
     return 0;
 
 pod_hit:
     page_list_add_tail(p, &d->arch.relmem_list);
-    spin_unlock(&d->page_alloc_lock);
+    unlock_page_alloc(p2m);
     return 1;
 }
 
@@ -994,7 +1008,7 @@ p2m_pod_demand_populate(struct p2m_domai
     if ( q == p2m_guest && gfn > p2m->pod.max_guest )
         p2m->pod.max_guest = gfn;
 
-    spin_lock(&d->page_alloc_lock);
+    lock_page_alloc(p2m);
 
     if ( p2m->pod.count == 0 )
         goto out_of_memory;
@@ -1008,7 +1022,7 @@ p2m_pod_demand_populate(struct p2m_domai
 
     BUG_ON((mfn_x(mfn) & ((1 << order)-1)) != 0);
 
-    spin_unlock(&d->page_alloc_lock);
+    unlock_page_alloc(p2m);
 
     gfn_aligned = (gfn >> order) << order;
 
@@ -1040,7 +1054,7 @@ p2m_pod_demand_populate(struct p2m_domai
 
     return 0;
 out_of_memory:
-    spin_unlock(&d->page_alloc_lock);
+    unlock_page_alloc(p2m);
 
     printk("%s: Out of populate-on-demand memory! tot_pages %" PRIu32 " 
pod_entries %" PRIi32 "\n",
            __func__, d->tot_pages, p2m->pod.entry_count);
@@ -1049,7 +1063,7 @@ out_fail:
     return -1;
 remap_and_retry:
     BUG_ON(order != PAGE_ORDER_2M);
-    spin_unlock(&d->page_alloc_lock);
+    unlock_page_alloc(p2m);
 
     /* Remap this 2-meg region in singleton chunks */
     gfn_aligned = (gfn>>order)<<order;
diff -r 81eedccb3a85 -r 0e8fb21ab4ff xen/include/asm-x86/domain.h
--- a/xen/include/asm-x86/domain.h
+++ b/xen/include/asm-x86/domain.h
@@ -269,6 +269,9 @@ struct arch_domain
 
     struct paging_domain paging;
     struct p2m_domain *p2m;
+    /* To enforce lock ordering in the pod code wrt the 
+     * page_alloc lock */
+    int page_alloc_unlock_level;
 
     /* nestedhvm: translate l2 guest physical to host physical */
     struct p2m_domain *nested_p2m[MAX_NESTEDP2M];
diff -r 81eedccb3a85 -r 0e8fb21ab4ff xen/include/asm-x86/p2m.h
--- a/xen/include/asm-x86/p2m.h
+++ b/xen/include/asm-x86/p2m.h
@@ -270,6 +270,11 @@ struct p2m_domain {
      * + p2m_pod_demand_populate() grabs both; the p2m lock to avoid
      *   double-demand-populating of pages, the page_alloc lock to
      *   protect moving stuff from the PoD cache to the domain page list.
+     *
+     * We enforce this lock ordering through a construct in mm-locks.h.
+     * This demands, however, that we store the previous lock-ordering
+     * level in effect before grabbing the page_alloc lock. The unlock
+     * level is stored in the arch section of the domain struct.
      */
     struct {
         struct page_list_head super,   /* List of superpages                */

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