x86/mm: Make {hap, shadow}_teardown() preemptible

A domain with sufficient shadow allocation can cause a watchdog timeout
during domain destruction.  Expand the existing -EAGAIN logic in
paging_teardown() to allow {hap/sh}_set_allocation() to become
restartable during the DOMCTL_destroydomain hypercall.

Signed-off-by: Anshul Makkar <anshul.makkar@citrix.com>
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Tim Deegan <tim@xen.org>
Reviewed-by: George Dunlap <george.dunlap@eu.citrix.com>
master commit: 0174da5b79
master date: 2015-08-06 10:04:43 +0100

xen/arch/x86/mm/hap/hap.c

@@ -498,7 +498,7 @@ void hap_final_teardown(struct domain *d)
     }
 
     if ( d->arch.paging.hap.total_pages != 0 )
-        hap_teardown(d);
+        hap_teardown(d, NULL);
 
     p2m_teardown(p2m_get_hostp2m(d));
     /* Free any memory that the p2m teardown released */
@@ -508,7 +508,7 @@ void hap_final_teardown(struct domain *d)
     paging_unlock(d);
 }
 
-void hap_teardown(struct domain *d)
+void hap_teardown(struct domain *d, int *preempted)
 {
     struct vcpu *v;
     mfn_t mfn;
@@ -536,18 +536,11 @@ void hap_teardown(struct domain *d)
 
     if ( d->arch.paging.hap.total_pages != 0 )
     {
-        HAP_PRINTK("teardown of domain %u starts."
-                      "  pages total = %u, free = %u, p2m=%u\n",
-                      d->domain_id,
-                      d->arch.paging.hap.total_pages,
-                      d->arch.paging.hap.free_pages,
-                      d->arch.paging.hap.p2m_pages);
-        hap_set_allocation(d, 0, NULL);
-        HAP_PRINTK("teardown done."
-                      "  pages total = %u, free = %u, p2m=%u\n",
-                      d->arch.paging.hap.total_pages,
-                      d->arch.paging.hap.free_pages,
-                      d->arch.paging.hap.p2m_pages);
+        hap_set_allocation(d, 0, preempted);
+
+        if ( preempted && *preempted )
+            goto out;
+
         ASSERT(d->arch.paging.hap.total_pages == 0);
     }
 
@@ -556,6 +549,7 @@ void hap_teardown(struct domain *d)
     xfree(d->arch.hvm_domain.dirty_vram);
     d->arch.hvm_domain.dirty_vram = NULL;
 
+out:
     paging_unlock(d);
 }
 

xen/arch/x86/mm/paging.c

@@ -777,12 +777,15 @@ long paging_domctl_continuation(XEN_GUEST_HANDLE_PARAM(xen_domctl_t) u_domctl)
 /* Call when destroying a domain */
 int paging_teardown(struct domain *d)
 {
-    int rc;
+    int rc, preempted = 0;
 
     if ( hap_enabled(d) )
-        hap_teardown(d);
+        hap_teardown(d, &preempted);
     else
-        shadow_teardown(d);
+        shadow_teardown(d, &preempted);
+
+    if ( preempted )
+        return -EAGAIN;
 
     /* clean up log dirty resources. */
     rc = paging_free_log_dirty_bitmap(d, 0);

xen/arch/x86/mm/shadow/common.c

@@ -3031,7 +3031,7 @@ int shadow_enable(struct domain *d, u32 mode)
     return rv;
 }
 
-void shadow_teardown(struct domain *d)
+void shadow_teardown(struct domain *d, int *preempted)
 /* Destroy the shadow pagetables of this domain and free its shadow memory.
  * Should only be called for dying domains. */
 {
@@ -3092,23 +3092,16 @@ void shadow_teardown(struct domain *d)
 
     if ( d->arch.paging.shadow.total_pages != 0 )
     {
-        SHADOW_PRINTK("teardown of domain %u starts."
-                       "  Shadow pages total = %u, free = %u, p2m=%u\n",
-                       d->domain_id,
-                       d->arch.paging.shadow.total_pages, 
-                       d->arch.paging.shadow.free_pages, 
-                       d->arch.paging.shadow.p2m_pages);
         /* Destroy all the shadows and release memory to domheap */
-        sh_set_allocation(d, 0, NULL);
+        sh_set_allocation(d, 0, preempted);
+
+        if ( preempted && *preempted )
+            goto out;
+
         /* Release the hash table back to xenheap */
         if (d->arch.paging.shadow.hash_table) 
             shadow_hash_teardown(d);
-        /* Should not have any more memory held */
-        SHADOW_PRINTK("teardown done."
-                       "  Shadow pages total = %u, free = %u, p2m=%u\n",
-                       d->arch.paging.shadow.total_pages, 
-                       d->arch.paging.shadow.free_pages, 
-                       d->arch.paging.shadow.p2m_pages);
+
         ASSERT(d->arch.paging.shadow.total_pages == 0);
     }
 
@@ -3139,6 +3132,7 @@ void shadow_teardown(struct domain *d)
         d->arch.hvm_domain.dirty_vram = NULL;
     }
 
+out:
     paging_unlock(d);
 
     /* Must be called outside the lock */
@@ -3160,7 +3154,7 @@ void shadow_final_teardown(struct domain *d)
      * It is possible for a domain that never got domain_kill()ed
      * to get here with its shadow allocation intact. */
     if ( d->arch.paging.shadow.total_pages != 0 )
-        shadow_teardown(d);
+        shadow_teardown(d, NULL);
 
     /* It is now safe to pull down the p2m map. */
     p2m_teardown(p2m_get_hostp2m(d));

xen/include/asm-x86/hap.h

@@ -54,7 +54,7 @@ int   hap_domctl(struct domain *d, xen_domctl_shadow_op_t *sc,
                  XEN_GUEST_HANDLE_PARAM(void) u_domctl);
 int   hap_enable(struct domain *d, u32 mode);
 void  hap_final_teardown(struct domain *d);
-void  hap_teardown(struct domain *d);
+void  hap_teardown(struct domain *d, int *preempted);
 void  hap_vcpu_init(struct vcpu *v);
 void  hap_logdirty_init(struct domain *d);
 int   hap_track_dirty_vram(struct domain *d,

xen/include/asm-x86/shadow.h

@@ -76,7 +76,7 @@ int shadow_domctl(struct domain *d,
                   XEN_GUEST_HANDLE_PARAM(void) u_domctl);
 
 /* Call when destroying a domain */
-void shadow_teardown(struct domain *d);
+void shadow_teardown(struct domain *d, int *preempted);
 
 /* Call once all of the references to the domain have gone away */
 void shadow_final_teardown(struct domain *d);