altp2m: Allow shared entries to be copied to altp2m views during lazycopy

Move sharing locks above altp2m to avoid locking order violation and crashing
the hypervisor during unsharing operations when altp2m is active.

Applying mem_access settings or remapping gfns in altp2m views will
automatically unshare the page if it was shared previously. Also,
disallow nominating pages for which there are pre-existing altp2m
mem_access settings or remappings present. However, allow altp2m to
populate altp2m views with shared entries during lazycopy as unsharing
will automatically propagate the change to these entries in altp2m
views as well.

While we're here, switch to using the appropriate wrappers rather than
calling p2m->get_entry() directly.

Signed-off-by: Tamas K Lengyel <tamas.lengyel@zentific.com>
Reviewed-by: George Dunlap <george.dunlap@citrix.com>

diff --git a/xen/arch/x86/mm/mem_sharing.c b/xen/arch/x86/mm/mem_sharing.c
index a5224239df76f69d97d86fed44aa4ad1eed9980f..47e08209eb7aaaadf24ce3def9e6b5e450d13b0a 100644 (file)
--- a/xen/arch/x86/mm/mem_sharing.c
+++ b/xen/arch/x86/mm/mem_sharing.c
@@ -33,6 +33,7 @@
 #include <asm/page.h>
 #include <asm/string.h>
 #include <asm/p2m.h>
+#include <asm/altp2m.h>
 #include <asm/atomic.h>
 #include <asm/event.h>
 #include <xsm/xsm.h>
@@ -828,14 +829,16 @@ int mem_sharing_nominate_page(struct domain *d,
                               int expected_refcnt,
                               shr_handle_t *phandle)
 {
+    struct p2m_domain *hp2m = p2m_get_hostp2m(d);
     p2m_type_t p2mt;
+    p2m_access_t p2ma;
     mfn_t mfn;
     struct page_info *page = NULL; /* gcc... */
     int ret;
 
     *phandle = 0UL;
 
-    mfn = get_gfn(d, gfn, &p2mt);
+    mfn = get_gfn_type_access(hp2m, gfn, &p2mt, &p2ma, 0, NULL);
 
     /* Check if mfn is valid */
     ret = -EINVAL;
@@ -861,6 +864,33 @@ int mem_sharing_nominate_page(struct domain *d,
     if ( !p2m_is_sharable(p2mt) )
         goto out;
 
+    /* Check if there are mem_access/remapped altp2m entries for this page */
+    if ( altp2m_active(d) )
+    {
+        unsigned int i;
+        struct p2m_domain *ap2m;
+        mfn_t amfn;
+        p2m_access_t ap2ma;
+
+        altp2m_list_lock(d);
+
+        for ( i = 0; i < MAX_ALTP2M; i++ )
+        {
+            ap2m = d->arch.altp2m_p2m[i];
+            if ( !ap2m )
+                continue;
+
+            amfn = get_gfn_type_access(ap2m, gfn, NULL, &ap2ma, 0, NULL);
+            if ( mfn_valid(amfn) && (mfn_x(amfn) != mfn_x(mfn) || ap2ma != p2ma) )
+            {
+                altp2m_list_unlock(d);
+                goto out;
+            }
+        }
+
+        altp2m_list_unlock(d);
+    }
+
     /* Try to convert the mfn to the sharable type */
     page = mfn_to_page(mfn);
     ret = page_make_sharable(d, page, expected_refcnt); 

diff --git a/xen/arch/x86/mm/mm-locks.h b/xen/arch/x86/mm/mm-locks.h
index 086c8bb4e17959da2d3a6e3cd2a50d60292667c0..74fdfc18e81610116403f833ecc5d496df75d4b1 100644 (file)
--- a/xen/arch/x86/mm/mm-locks.h
+++ b/xen/arch/x86/mm/mm-locks.h
@@ -242,6 +242,21 @@ declare_mm_lock(nestedp2m)
 
 declare_mm_rwlock(p2m);
 
+/* Sharing per page lock
+ *
+ * This is an external lock, not represented by an mm_lock_t. The memory
+ * sharing lock uses it to protect addition and removal of (gfn,domain)
+ * tuples to a shared page. We enforce order here against the p2m lock,
+ * which is taken after the page_lock to change the gfn's p2m entry.
+ *
+ * The lock is recursive because during share we lock two pages. */
+
+declare_mm_order_constraint(per_page_sharing)
+#define page_sharing_mm_pre_lock()   mm_enforce_order_lock_pre_per_page_sharing()
+#define page_sharing_mm_post_lock(l, r) \
+        mm_enforce_order_lock_post_per_page_sharing((l), (r))
+#define page_sharing_mm_unlock(l, r) mm_enforce_order_unlock((l), (r))
+
 /* Alternate P2M list lock (per-domain)
  *
  * A per-domain lock that protects the list of alternate p2m's.
@@ -287,21 +302,6 @@ declare_mm_rwlock(altp2m);
 #define p2m_locked_by_me(p)   mm_write_locked_by_me(&(p)->lock)
 #define gfn_locked_by_me(p,g) p2m_locked_by_me(p)
 
-/* Sharing per page lock
- *
- * This is an external lock, not represented by an mm_lock_t. The memory
- * sharing lock uses it to protect addition and removal of (gfn,domain)
- * tuples to a shared page. We enforce order here against the p2m lock,
- * which is taken after the page_lock to change the gfn's p2m entry.
- *
- * The lock is recursive because during share we lock two pages. */
-
-declare_mm_order_constraint(per_page_sharing)
-#define page_sharing_mm_pre_lock()   mm_enforce_order_lock_pre_per_page_sharing()
-#define page_sharing_mm_post_lock(l, r) \
-        mm_enforce_order_lock_post_per_page_sharing((l), (r))
-#define page_sharing_mm_unlock(l, r) mm_enforce_order_unlock((l), (r))
-
 /* PoD lock (per-p2m-table)
  * 
  * Protects private PoD data structs: entry and cache

diff --git a/xen/arch/x86/mm/p2m.c b/xen/arch/x86/mm/p2m.c
index ff0cce8a692c1be6ee9a22608541e1400349a631..812dbf67deede3a04858e7c56ebfe9648a4bde23 100644 (file)
--- a/xen/arch/x86/mm/p2m.c
+++ b/xen/arch/x86/mm/p2m.c
@@ -1786,8 +1786,9 @@ int p2m_set_altp2m_mem_access(struct domain *d, struct p2m_domain *hp2m,
     /* Check host p2m if no valid entry in alternate */
     if ( !mfn_valid(mfn) )
     {
-        mfn = hp2m->get_entry(hp2m, gfn_l, &t, &old_a,
-                              P2M_ALLOC | P2M_UNSHARE, &page_order, NULL);
+
+        mfn = get_gfn_type_access(hp2m, gfn_l, &t, &old_a,
+                                  P2M_ALLOC | P2M_UNSHARE, &page_order);
 
         rc = -ESRCH;
         if ( !mfn_valid(mfn) || t != p2m_ram_rw )
@@ -2363,7 +2364,7 @@ bool_t p2m_altp2m_lazy_copy(struct vcpu *v, paddr_t gpa,
         return 0;
 
     mfn = get_gfn_type_access(hp2m, gfn_x(gfn), &p2mt, &p2ma,
-                              P2M_ALLOC | P2M_UNSHARE, &page_order);
+                              P2M_ALLOC, &page_order);
     __put_gfn(hp2m, gfn_x(gfn));
 
     if ( mfn_eq(mfn, INVALID_MFN) )
@@ -2562,8 +2563,8 @@ int p2m_change_altp2m_gfn(struct domain *d, unsigned int idx,
     /* Check host p2m if no valid entry in alternate */
     if ( !mfn_valid(mfn) )
     {
-        mfn = hp2m->get_entry(hp2m, gfn_x(old_gfn), &t, &a,
-                              P2M_ALLOC | P2M_UNSHARE, &page_order, NULL);
+        mfn = get_gfn_type_access(hp2m, gfn_x(old_gfn), &t, &a,
+                                  P2M_ALLOC | P2M_UNSHARE, &page_order);
 
         if ( !mfn_valid(mfn) || t != p2m_ram_rw )
             goto out;
@@ -2588,6 +2589,7 @@ int p2m_change_altp2m_gfn(struct domain *d, unsigned int idx,
     if ( !mfn_valid(mfn) )
         mfn = hp2m->get_entry(hp2m, gfn_x(new_gfn), &t, &a, 0, NULL, NULL);
 
+    /* Note: currently it is not safe to remap to a shared entry */
     if ( !mfn_valid(mfn) || (t != p2m_ram_rw) )
         goto out;