xen/arch/x86/mm/mm-locks.h | 11 +++++++++++
xen/arch/x86/mm/p2m-pod.c | 40 +++++++++++++++++++++++++++-------------
xen/include/asm-x86/p2m.h | 5 +++++
3 files changed, 43 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.
Signed-off-by: Andres Lagar-Cavilla <andres@xxxxxxxxxxxxxxxx>
diff -r c915609e4235 -r 332775f72a30 xen/arch/x86/mm/mm-locks.h
--- a/xen/arch/x86/mm/mm-locks.h
+++ b/xen/arch/x86/mm/mm-locks.h
@@ -155,6 +155,17 @@ 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 */
+
+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))
+#define page_alloc_mm_unlock(l) mm_enforce_order_unlock((l))
+
/* Paging lock (per-domain)
*
* For shadow pagetables, this lock protects
diff -r c915609e4235 -r 332775f72a30 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->pod.page_alloc_unlock_level);
+}
+
+static inline void unlock_page_alloc(struct p2m_domain *p2m)
+{
+ page_alloc_mm_unlock(p2m->pod.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 c915609e4235 -r 332775f72a30 xen/include/asm-x86/p2m.h
--- a/xen/include/asm-x86/p2m.h
+++ b/xen/include/asm-x86/p2m.h
@@ -270,6 +270,10 @@ 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.
*/
struct {
struct page_list_head super, /* List of superpages */
@@ -279,6 +283,7 @@ struct p2m_domain {
unsigned reclaim_super; /* Last gpfn of a scan */
unsigned reclaim_single; /* Last gpfn of a scan */
unsigned max_guest; /* gpfn of max guest demand-populate */
+ int page_alloc_unlock_level; /* To enforce lock ordering
*/
} pod;
};
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