[xen stable-4.16] x86: perform mem_sharing teardown before paging teardown

[patchbot@xxxxxxx]

commit 700320a79297fb5087f7dd540424c468b2d2cffe
Author:     Tamas K Lengyel <tamas@xxxxxxxxxxxxx>
AuthorDate: Fri Mar 3 08:14:25 2023 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Fri Mar 3 08:14:25 2023 +0100

    x86: perform mem_sharing teardown before paging teardown
    
    An assert failure has been observed in p2m_teardown when performing vm
    forking and then destroying the forked VM (p2m-basic.c:173). The assert
    checks whether the domain's shared pages counter is 0. According to the
    patch that originally added the assert (7bedbbb5c31) the p2m_teardown
    should only happen after mem_sharing already relinquished all shared pages.
    
    In this patch we flip the order in which relinquish ops are called to avoid
    tripping the assert. Conceptually sharing being torn down makes sense to
    happen before paging is torn down.
    
    Fixes: e7aa55c0aab3 ("x86/p2m: free the paging memory pool preemptively")
    Signed-off-by: Tamas K Lengyel <tamas@xxxxxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
    master commit: 2869349f0cb3a89dcbf1f1b30371f58df6309312
    master date: 2023-02-23 12:35:48 +0100
---
 xen/arch/x86/domain.c | 56 ++++++++++++++++++++++++++-------------------------
 1 file changed, 29 insertions(+), 27 deletions(-)

diff --git a/xen/arch/x86/domain.c b/xen/arch/x86/domain.c
index 3080cde62b..6eeb248908 100644
--- a/xen/arch/x86/domain.c
+++ b/xen/arch/x86/domain.c
@@ -2343,9 +2343,9 @@ int domain_relinquish_resources(struct domain *d)
 
         enum {
             PROG_iommu_pagetables = 1,
+            PROG_shared,
             PROG_paging,
             PROG_vcpu_pagetables,
-            PROG_shared,
             PROG_xen,
             PROG_l4,
             PROG_l3,
@@ -2364,6 +2364,34 @@ int domain_relinquish_resources(struct domain *d)
         if ( ret )
             return ret;
 
+#ifdef CONFIG_MEM_SHARING
+    PROGRESS(shared):
+
+        if ( is_hvm_domain(d) )
+        {
+            /*
+             * If the domain has shared pages, relinquish them allowing
+             * for preemption.
+             */
+            ret = relinquish_shared_pages(d);
+            if ( ret )
+                return ret;
+
+            /*
+             * If the domain is forked, decrement the parent's pause count
+             * and release the domain.
+             */
+            if ( mem_sharing_is_fork(d) )
+            {
+                struct domain *parent = d->parent;
+
+                d->parent = NULL;
+                domain_unpause(parent);
+                put_domain(parent);
+            }
+        }
+#endif
+
     PROGRESS(paging):
 
         /* Tear down paging-assistance stuff. */
@@ -2404,32 +2432,6 @@ int domain_relinquish_resources(struct domain *d)
             d->arch.auto_unmask = 0;
         }
 
-#ifdef CONFIG_MEM_SHARING
-    PROGRESS(shared):
-
-        if ( is_hvm_domain(d) )
-        {
-            /* If the domain has shared pages, relinquish them allowing
-             * for preemption. */
-            ret = relinquish_shared_pages(d);
-            if ( ret )
-                return ret;
-
-            /*
-             * If the domain is forked, decrement the parent's pause count
-             * and release the domain.
-             */
-            if ( mem_sharing_is_fork(d) )
-            {
-                struct domain *parent = d->parent;
-
-                d->parent = NULL;
-                domain_unpause(parent);
-                put_domain(parent);
-            }
-        }
-#endif
-
         spin_lock(&d->page_alloc_lock);
         page_list_splice(&d->arch.relmem_list, &d->page_list);
         INIT_PAGE_LIST_HEAD(&d->arch.relmem_list);
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.16