[PATCH v5 01/11] memory: batch processing in acquire_resource()

["Michał Leszczyński" <michal.leszczynski@cert.pl>]

From: Michal Leszczynski <michal.leszczynski@cert.pl>

Allow to acquire large resources by allowing acquire_resource()
to process items in batches, using hypercall continuation.

Be aware that this modifies the behavior of acquire_resource
call with frame_list=NULL. While previously it would return
the size of internal array (32), with this patch it returns
the maximal quantity of frames that could be requested at once,
i.e. UINT_MAX >> MEMOP_EXTENT_SHIFT.

Signed-off-by: Michal Leszczynski <michal.leszczynski@cert.pl>
---
 xen/common/memory.c | 49 ++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 44 insertions(+), 5 deletions(-)

diff --git a/xen/common/memory.c b/xen/common/memory.c
index 714077c1e5..eb42f883df 100644
--- a/xen/common/memory.c
+++ b/xen/common/memory.c
@@ -1046,10 +1046,12 @@ static int acquire_grant_table(struct domain *d, unsigned int id,
 }
 
 static int acquire_resource(
-    XEN_GUEST_HANDLE_PARAM(xen_mem_acquire_resource_t) arg)
+    XEN_GUEST_HANDLE_PARAM(xen_mem_acquire_resource_t) arg,
+    unsigned long *start_extent)
 {
     struct domain *d, *currd = current->domain;
     xen_mem_acquire_resource_t xmar;
+    uint32_t total_frames;
     /*
      * The mfn_list and gfn_list (below) arrays are ok on stack for the
      * moment since they are small, but if they need to grow in future
@@ -1069,7 +1071,7 @@ static int acquire_resource(
         if ( xmar.nr_frames )
             return -EINVAL;
 
-        xmar.nr_frames = ARRAY_SIZE(mfn_list);
+        xmar.nr_frames = UINT_MAX >> MEMOP_EXTENT_SHIFT;
 
         if ( __copy_field_to_guest(arg, &xmar, nr_frames) )
             return -EFAULT;
@@ -1077,8 +1079,28 @@ static int acquire_resource(
         return 0;
     }
 
+    total_frames = xmar.nr_frames;
+
+    /* Is the size too large for us to encode a continuation? */
+    if ( unlikely(xmar.nr_frames > (UINT_MAX >> MEMOP_EXTENT_SHIFT)) )
+        return -EINVAL;
+
+    if ( *start_extent )
+    {
+        /*
+         * Check whether start_extent is in bounds, as this
+         * value if visible to the calling domain.
+         */
+        if ( *start_extent > xmar.nr_frames )
+            return -EINVAL;
+
+        xmar.frame += *start_extent;
+        xmar.nr_frames -= *start_extent;
+        guest_handle_add_offset(xmar.frame_list, *start_extent);
+    }
+
     if ( xmar.nr_frames > ARRAY_SIZE(mfn_list) )
-        return -E2BIG;
+        xmar.nr_frames = ARRAY_SIZE(mfn_list);
 
     rc = rcu_lock_remote_domain_by_id(xmar.domid, &d);
     if ( rc )
@@ -1135,6 +1157,14 @@ static int acquire_resource(
         }
     }
 
+    if ( !rc )
+    {
+        *start_extent += xmar.nr_frames;
+
+        if ( *start_extent != total_frames )
+            rc = -ERESTART;
+    }
+
  out:
     rcu_unlock_domain(d);
 
@@ -1599,8 +1629,17 @@ long do_memory_op(unsigned long cmd, XEN_GUEST_HANDLE_PARAM(void) arg)
 #endif
 
     case XENMEM_acquire_resource:
-        rc = acquire_resource(
-            guest_handle_cast(arg, xen_mem_acquire_resource_t));
+        do {
+            rc = acquire_resource(
+                guest_handle_cast(arg, xen_mem_acquire_resource_t),
+                &start_extent);
+
+            if ( hypercall_preempt_check() )
+                return hypercall_create_continuation(
+                    __HYPERVISOR_memory_op, "lh",
+                    op | (start_extent << MEMOP_EXTENT_SHIFT), arg);
+        } while ( rc == -ERESTART );
+
         break;
 
     default:
-- 
2.17.1