RE: [PATCH] Enhance memory exchange to support foreign domain -- Was RE: [Xen-devel] [PATCH 6/6] Change MMU_PT_UPDATE_RESERVE_AD to support update page table for foreign domain

["Jiang, Yunhong" <yunhong.jiang@xxxxxxxxx>]

Attached is the updated patch. I tried to call domain_kill() duing 
memory_exchange, and do hit the situation that assign_pages will fail because 
of domain dying. The domain can be killed cleanly still, no zombie domain left.

Changes from previous submission: a) lock protection for tot_pages, b) free the 
page that has been moved out of the out_chunk_list.

Thanks
Yunhong Jiang


diff -r 02003bee3e80 xen/common/memory.c
--- a/xen/common/memory.c       Thu Jun 25 18:31:10 2009 +0100
+++ b/xen/common/memory.c       Wed Jul 01 19:55:23 2009 +0800
@@ -265,16 +265,22 @@ static long memory_exchange(XEN_GUEST_HA
         out_chunk_order = exch.in.extent_order - exch.out.extent_order;
     }
 
-    /*
-     * Only support exchange on calling domain right now. Otherwise there are
-     * tricky corner cases to consider (e.g., dying domain).
-     */
-    if ( unlikely(exch.in.domid != DOMID_SELF) )
-    {
-        rc = IS_PRIV(current->domain) ? -EINVAL : -EPERM;
-        goto fail_early;
-    }
-    d = current->domain;
+    if ( likely(exch.in.domid == DOMID_SELF) )
+    {
+        d = rcu_lock_current_domain();
+    }
+    else
+    {
+        if ( (d = rcu_lock_domain_by_id(exch.in.domid)) == NULL )
+            goto fail_early;
+
+        if ( !IS_PRIV_FOR(current->domain, d) )
+        {
+            rcu_unlock_domain(d);
+            rc = -EPERM;
+            goto fail_early;
+        }
+    }
 
     memflags |= MEMF_bits(domain_clamp_alloc_bitsize(
         d,
@@ -292,6 +298,7 @@ static long memory_exchange(XEN_GUEST_HA
         if ( hypercall_preempt_check() )
         {
             exch.nr_exchanged = i << in_chunk_order;
+            rcu_unlock_domain(d);
             if ( copy_field_to_guest(arg, &exch, nr_exchanged) )
                 return -EFAULT;
             return hypercall_create_continuation(
@@ -360,9 +367,39 @@ static long memory_exchange(XEN_GUEST_HA
         j = 0;
         while ( (page = page_list_remove_head(&out_chunk_list)) )
         {
-            if ( assign_pages(d, page, exch.out.extent_order,
-                              MEMF_no_refcount) )
+            rc = (assign_pages(d, page, exch.out.extent_order,
+                              MEMF_no_refcount));
+
+            if (rc == -EINVAL)
                 BUG();
+            /* Domain is being destroy */
+            else if (rc == -ENODEV)
+            {
+                int dec_count, drop_dom_ref = 0;
+
+                /*
+                 * Pages in in_chunk_list is stolen without
+                 * decreasing the tot_pages. If the domain is dying when
+                 * assign pages, we need decrease the count. For those pages
+                 * that has been assigned, it should be covered by
+                 * domain_relinquish_resources().
+                 */
+                dec_count =  ( ( 1UL << exch.in.extent_order)*
+                                     (1UL << in_chunk_order) -
+                               j * (1UL << exch.out.extent_order));
+
+                spin_lock(&d->page_alloc_lock);
+                d->tot_pages -= dec_count;
+                if (dec_count && !d->tot_pages)
+                    drop_dom_ref = 1;
+                spin_unlock(&d->page_alloc_lock);
+
+                if (drop_dom_ref)
+                    put_domain(d);
+
+                free_domheap_pages(page, exch.out.extent_order);
+                goto dying;
+            }
 
             /* Note that we ignore errors accessing the output extent list. */
             (void)__copy_from_guest_offset(
@@ -378,15 +415,15 @@ static long memory_exchange(XEN_GUEST_HA
                 (void)__copy_to_guest_offset(
                     exch.out.extent_start, (i<<out_chunk_order)+j, &mfn, 1);
             }
-
             j++;
         }
-        BUG_ON(j != (1UL << out_chunk_order));
+        BUG_ON( !(d->is_dying) && (j != (1UL << out_chunk_order)) );
     }
 
     exch.nr_exchanged = exch.in.nr_extents;
     if ( copy_field_to_guest(arg, &exch, nr_exchanged) )
         rc = -EFAULT;
+    rcu_unlock_domain(d);
     return rc;
 
     /*
@@ -398,7 +435,8 @@ static long memory_exchange(XEN_GUEST_HA
     while ( (page = page_list_remove_head(&in_chunk_list)) )
         if ( assign_pages(d, page, 0, MEMF_no_refcount) )
             BUG();
-
+ dying:
+    rcu_unlock_domain(d);
     /* Free any output pages we managed to allocate. */
     while ( (page = page_list_remove_head(&out_chunk_list)) )
         free_domheap_pages(page, exch.out.extent_order);
diff -r 02003bee3e80 xen/common/page_alloc.c
--- a/xen/common/page_alloc.c   Thu Jun 25 18:31:10 2009 +0100
+++ b/xen/common/page_alloc.c   Tue Jun 30 23:33:47 2009 +0800
@@ -1120,6 +1120,7 @@ int assign_pages(
     unsigned int memflags)
 {
     unsigned long i;
+    int rc = -EINVAL;
 
     spin_lock(&d->page_alloc_lock);
 
@@ -1127,6 +1128,7 @@ int assign_pages(
     {
         gdprintk(XENLOG_INFO, "Cannot assign page to domain%d -- dying.\n",
                 d->domain_id);
+                rc = -ENODEV;
         goto fail;
     }
 
@@ -1136,6 +1138,7 @@ int assign_pages(
         {
             gdprintk(XENLOG_INFO, "Over-allocation for domain %u: %u > %u\n",
                     d->domain_id, d->tot_pages + (1 << order), d->max_pages);
+            rc = -EINVAL;
             goto fail;
         }
 
@@ -1160,7 +1163,7 @@ int assign_pages(
 
  fail:
     spin_unlock(&d->page_alloc_lock);
-    return -1;
+    return rc;
 }
 
 



Keir Fraser wrote:
> On 30/06/2009 10:40, "Jiang, Yunhong" <yunhong.jiang@xxxxxxxxx> wrote:
> 
>>> B. Your adjustment of tot_pages is confusing. I can't convince
>>> myself the arithmetic is correct. Furthermore messing with
>>> tot_pages outside of the d->page_alloc_lock is not allowed.
>> 
>> The idea of the adjustment is:
>> 
>> In each loop, we remove some pages (the in_chunk_list) without
>> decrease the tot_pages. Then when we get domain is dying when assign
>> pages (the out_chunk_list), we need decrease the count. For those
>> page that has been assigned, it should be covered by
> domain_relinquish_resources(), so what we
>> need decrease is:
>> the number that has been removed - the number that has been assigned
>> already. 
> 
> There's still quite a logical leap to the arithmetic in your
> code. Spell it
> out in a comment.
> 
> -- Keir

Attachment: memory_exchange_v2.patch
Description: memory_exchange_v2.patch

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