[Xen-changelog] [xen stable-4.6] x86/PV: fix unintended dependency of m2p-strict mode on migration-v2

[patchbot@xxxxxxx]

commit cf5273420a1505b35ec974f3c20c410f4999a190
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Wed Feb 17 16:39:49 2016 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Wed Feb 17 16:39:49 2016 +0100

    x86/PV: fix unintended dependency of m2p-strict mode on migration-v2
    
    This went unnoticed until a backport of this to an older Xen got used,
    causing migration of guests enabling this VM assist to fail, because
    page table pinning there precedes vCPU context loading, and hence L4
    tables get initialized for the wrong mode. Fix this by post-processing
    L4 tables when setting the intended VM assist flags for the guest.
    
    Note that this leaves in place a dependency on vCPU 0 getting its guest
    context restored first, but afaict the logic here is not the only thing
    depending on that.
    
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    master commit: be05b5385fb261c1fa1cbb6b4bdc12a6e8676c4b
    master date: 2016-02-03 14:12:00 +0100
---
 xen/arch/x86/domain.c        | 41 +++++++++++++++++++++++++++++++++++++++++
 xen/arch/x86/mm.c            | 30 ++++++++++++++++++++++++------
 xen/include/asm-x86/domain.h |  2 ++
 xen/include/asm-x86/mm.h     |  2 +-
 4 files changed, 68 insertions(+), 7 deletions(-)

diff --git a/xen/arch/x86/domain.c b/xen/arch/x86/domain.c
index 54f5875..90f3ce5 100644
--- a/xen/arch/x86/domain.c
+++ b/xen/arch/x86/domain.c
@@ -991,7 +991,48 @@ int arch_set_info_guest(
         goto out;
 
     if ( v->vcpu_id == 0 )
+    {
+        /*
+         * In the restore case we need to deal with L4 pages which got
+         * initialized with m2p_strict still clear (and which hence lack the
+         * correct initial RO_MPT_VIRT_{START,END} L4 entry).
+         */
+        if ( d != current->domain && !VM_ASSIST(d, m2p_strict) &&
+             is_pv_domain(d) && !is_pv_32bit_domain(d) &&
+             test_bit(VMASST_TYPE_m2p_strict, &c.nat->vm_assist) &&
+             atomic_read(&d->arch.pv_domain.nr_l4_pages) )
+        {
+            bool_t done = 0;
+
+            spin_lock_recursive(&d->page_alloc_lock);
+
+            for ( i = 0; ; )
+            {
+                struct page_info *page = page_list_remove_head(&d->page_list);
+
+                if ( page_lock(page) )
+                {
+                    if ( (page->u.inuse.type_info & PGT_type_mask) ==
+                         PGT_l4_page_table )
+                        done = !fill_ro_mpt(page_to_mfn(page));
+
+                    page_unlock(page);
+                }
+
+                page_list_add_tail(page, &d->page_list);
+
+                if ( done || (!(++i & 0xff) && hypercall_preempt_check()) )
+                    break;
+            }
+
+            spin_unlock_recursive(&d->page_alloc_lock);
+
+            if ( !done )
+                return -ERESTART;
+        }
+
         d->vm_assist = c(vm_assist);
+    }
 
     rc = put_old_guest_table(current);
     if ( rc )
diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c
index 17644aa..63c9bcf 100644
--- a/xen/arch/x86/mm.c
+++ b/xen/arch/x86/mm.c
@@ -1493,13 +1493,20 @@ void init_guest_l4_table(l4_pgentry_t l4tab[], const 
struct domain *d,
         l4tab[l4_table_offset(RO_MPT_VIRT_START)] = l4e_empty();
 }
 
-void fill_ro_mpt(unsigned long mfn)
+bool_t fill_ro_mpt(unsigned long mfn)
 {
     l4_pgentry_t *l4tab = map_domain_page(_mfn(mfn));
+    bool_t ret = 0;
 
-    l4tab[l4_table_offset(RO_MPT_VIRT_START)] =
-        idle_pg_table[l4_table_offset(RO_MPT_VIRT_START)];
+    if ( !l4e_get_intpte(l4tab[l4_table_offset(RO_MPT_VIRT_START)]) )
+    {
+        l4tab[l4_table_offset(RO_MPT_VIRT_START)] =
+            idle_pg_table[l4_table_offset(RO_MPT_VIRT_START)];
+        ret = 1;
+    }
     unmap_domain_page(l4tab);
+
+    return ret;
 }
 
 void zap_ro_mpt(unsigned long mfn)
@@ -1557,10 +1564,15 @@ static int alloc_l4_table(struct page_info *page)
         adjust_guest_l4e(pl4e[i], d);
     }
 
-    init_guest_l4_table(pl4e, d, !VM_ASSIST(d, m2p_strict));
+    if ( rc >= 0 )
+    {
+        init_guest_l4_table(pl4e, d, !VM_ASSIST(d, m2p_strict));
+        atomic_inc(&d->arch.pv_domain.nr_l4_pages);
+        rc = 0;
+    }
     unmap_domain_page(pl4e);
 
-    return rc > 0 ? 0 : rc;
+    return rc;
 }
 
 static void free_l1_table(struct page_info *page)
@@ -1678,7 +1690,13 @@ static int free_l4_table(struct page_info *page)
 
     unmap_domain_page(pl4e);
 
-    return rc > 0 ? 0 : rc;
+    if ( rc >= 0 )
+    {
+        atomic_dec(&d->arch.pv_domain.nr_l4_pages);
+        rc = 0;
+    }
+
+    return rc;
 }
 
 int page_lock(struct page_info *page)
diff --git a/xen/include/asm-x86/domain.h b/xen/include/asm-x86/domain.h
index 0fce09e..c6c6e71 100644
--- a/xen/include/asm-x86/domain.h
+++ b/xen/include/asm-x86/domain.h
@@ -247,6 +247,8 @@ struct pv_domain
 {
     l1_pgentry_t **gdt_ldt_l1tab;
 
+    atomic_t nr_l4_pages;
+
     /* map_domain_page() mapping cache. */
     struct mapcache_domain mapcache;
 };
diff --git a/xen/include/asm-x86/mm.h b/xen/include/asm-x86/mm.h
index b4075e6..b4299fd 100644
--- a/xen/include/asm-x86/mm.h
+++ b/xen/include/asm-x86/mm.h
@@ -321,7 +321,7 @@ int free_page_type(struct page_info *page, unsigned long 
type,
 
 void init_guest_l4_table(l4_pgentry_t[], const struct domain *,
                          bool_t zap_ro_mpt);
-void fill_ro_mpt(unsigned long mfn);
+bool_t fill_ro_mpt(unsigned long mfn);
 void zap_ro_mpt(unsigned long mfn);
 
 int is_iomem_page(unsigned long mfn);
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.6

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