[Xen-devel] [PATCH 1/4] x86/PoD: Make p2m_pod_empty_cache() restartable

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

This avoids a long running operation when destroying a domain with a
large PoD cache.

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: George Dunlap <george.dunlap@xxxxxxxxxxxxx>
---
 xen/arch/x86/mm/p2m-pod.c | 16 +++++++++++-----
 xen/arch/x86/mm/paging.c  |  2 +-
 xen/include/asm-x86/p2m.h |  2 +-
 3 files changed, 13 insertions(+), 7 deletions(-)

diff --git a/xen/arch/x86/mm/p2m-pod.c b/xen/arch/x86/mm/p2m-pod.c
index 2a6f125..be15cf3 100644
--- a/xen/arch/x86/mm/p2m-pod.c
+++ b/xen/arch/x86/mm/p2m-pod.c
@@ -374,11 +374,11 @@ p2m_pod_set_mem_target(struct domain *d, unsigned long 
target)
     return ret;
 }
 
-void
-p2m_pod_empty_cache(struct domain *d)
+int p2m_pod_empty_cache(struct domain *d)
 {
     struct p2m_domain *p2m = p2m_get_hostp2m(d);
     struct page_info *page;
+    unsigned int i;
 
     /* After this barrier no new PoD activities can happen. */
     BUG_ON(!d->is_dying);
@@ -388,8 +388,6 @@ p2m_pod_empty_cache(struct domain *d)
 
     while ( (page = page_list_remove_head(&p2m->pod.super)) )
     {
-        int i;
-            
         for ( i = 0 ; i < SUPERPAGE_PAGES ; i++ )
         {
             BUG_ON(page_get_owner(page + i) != d);
@@ -397,19 +395,27 @@ p2m_pod_empty_cache(struct domain *d)
         }
 
         p2m->pod.count -= SUPERPAGE_PAGES;
+
+        if ( hypercall_preempt_check() )
+            goto out;
     }
 
-    while ( (page = page_list_remove_head(&p2m->pod.single)) )
+    for ( i = 0; (page = page_list_remove_head(&p2m->pod.single)); ++i )
     {
         BUG_ON(page_get_owner(page) != d);
         page_list_add_tail(page, &d->page_list);
 
         p2m->pod.count -= 1;
+
+        if ( i && !(i & 511) && hypercall_preempt_check() )
+            goto out;
     }
 
     BUG_ON(p2m->pod.count != 0);
 
+ out:
     unlock_page_alloc(p2m);
+    return p2m->pod.count ? -ERESTART : 0;
 }
 
 int
diff --git a/xen/arch/x86/mm/paging.c b/xen/arch/x86/mm/paging.c
index 0bfb2be..c7d1943 100644
--- a/xen/arch/x86/mm/paging.c
+++ b/xen/arch/x86/mm/paging.c
@@ -824,7 +824,7 @@ int paging_teardown(struct domain *d)
         return rc;
 
     /* Move populate-on-demand cache back to domain_list for destruction */
-    p2m_pod_empty_cache(d);
+    rc = p2m_pod_empty_cache(d);
 
     return rc;
 }
diff --git a/xen/include/asm-x86/p2m.h b/xen/include/asm-x86/p2m.h
index b710b2c..d748557 100644
--- a/xen/include/asm-x86/p2m.h
+++ b/xen/include/asm-x86/p2m.h
@@ -588,7 +588,7 @@ void p2m_pod_dump_data(struct domain *d);
 
 /* Move all pages from the populate-on-demand cache to the domain page_list
  * (usually in preparation for domain destruction) */
-void p2m_pod_empty_cache(struct domain *d);
+int p2m_pod_empty_cache(struct domain *d);
 
 /* Set populate-on-demand cache size so that the total memory allocated to a
  * domain matches target */
-- 
2.1.4


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