[PATCH v2 12/13] x86/mm: update log-dirty bitmap when manipulating P2M

[Jan Beulich <jbeulich@xxxxxxxx>]

Just like for PV guests MMU_MACHPHYS_UPDATE implies marking of the
respective page as dirty, additions to a HVM guest's P2M should do so.

For HVM the opposite is also true: Pages being removed from the P2M are
no longer dirty at their prior GFN; there's no point in telling the tool
stack to try and copy that page, when this will fail anyway (until
perhaps a new page gets placed there). Introduce paging_mark_pfn_clean()
(intentionally without a paging_mark_clean() counterpart) to handle
this. Note that while there is an earlier call to set_gpfn_from_mfn() in
guest_physmap_add_entry(), but there's little reason to mark the page
clean there when later in the function it'll be marked dirty. This is
even more so given that at this point it's only the M2P that gets
updated, with the P2M still left unchanged.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
guest_physmap_add_entry()'s error handling looks bogus in this regard
anyway: If an error occurs before an MFN actually gets assciated with
the new GFN, the M2P entry ought to be restored imo. But of course a
guest is still hosed if the operation succeeds partially.

Note that I've not even checked mem-paging and mem-sharing code for
whether they may need similar adjustment. At least the latters is, aiui,
incompatible with log-dirty mode anyway.

--- a/xen/arch/x86/mm/p2m.c
+++ b/xen/arch/x86/mm/p2m.c
@@ -818,7 +818,10 @@ p2m_remove_page(struct p2m_domain *p2m,
         {
             p2m->get_entry(p2m, gfn_add(gfn, i), &t, &a, 0, NULL, NULL);
             if ( !p2m_is_grant(t) && !p2m_is_shared(t) && !p2m_is_foreign(t) )
+            {
                 set_gpfn_from_mfn(mfn_x(mfn) + i, INVALID_M2P_ENTRY);
+                paging_mark_pfn_clean(p2m->domain, _pfn(gfn_x(gfn) + i));
+            }
         }
     }
 
@@ -1027,8 +1030,11 @@ guest_physmap_add_entry(struct domain *d
         if ( !p2m_is_grant(t) )
         {
             for ( i = 0; i < (1UL << page_order); i++ )
+            {
                 set_gpfn_from_mfn(mfn_x(mfn_add(mfn, i)),
                                   gfn_x(gfn_add(gfn, i)));
+                paging_mark_pfn_dirty(d, _pfn(gfn_x(gfn) + i));
+            }
         }
     }
 
@@ -1314,6 +1320,7 @@ static int set_typed_p2m_entry(struct do
         {
             ASSERT(mfn_valid(mfn_add(omfn, i)));
             set_gpfn_from_mfn(mfn_x(omfn) + i, INVALID_M2P_ENTRY);
+            paging_mark_pfn_clean(d, _pfn(gfn_x(gfn) + i));
         }
 
         ioreq_request_mapcache_invalidate(d);
--- a/xen/arch/x86/mm/p2m-pod.c
+++ b/xen/arch/x86/mm/p2m-pod.c
@@ -645,7 +645,10 @@ p2m_pod_decrease_reservation(struct doma
             }
             p2m_tlb_flush_sync(p2m);
             for ( j = 0; j < n; ++j )
+            {
                 set_gpfn_from_mfn(mfn_x(mfn), INVALID_M2P_ENTRY);
+                paging_mark_pfn_clean(d, _pfn(gfn_x(gfn) + i + j));
+            }
             p2m_pod_cache_add(p2m, page, cur_order);
 
             ioreq_request_mapcache_invalidate(d);
--- a/xen/arch/x86/mm/paging.c
+++ b/xen/arch/x86/mm/paging.c
@@ -259,7 +259,7 @@ static int paging_log_dirty_disable(stru
 }
 
 /* Mark a page as dirty, with taking guest pfn as parameter */
-void paging_mark_pfn_dirty(struct domain *d, pfn_t pfn)
+static void mark_pfn_dirty(struct domain *d, pfn_t pfn, bool dirty)
 {
     bool changed;
     mfn_t mfn, *l4, *l3, *l2;
@@ -290,14 +290,15 @@ void paging_mark_pfn_dirty(struct domain
 
     if ( unlikely(!mfn_valid(d->arch.paging.log_dirty.top)) ) 
     {
-         d->arch.paging.log_dirty.top = paging_new_log_dirty_node(d);
+         if ( dirty )
+             d->arch.paging.log_dirty.top = paging_new_log_dirty_node(d);
          if ( unlikely(!mfn_valid(d->arch.paging.log_dirty.top)) )
              goto out;
     }
 
     l4 = paging_map_log_dirty_bitmap(d);
     mfn = l4[i4];
-    if ( !mfn_valid(mfn) )
+    if ( !mfn_valid(mfn) && dirty )
         l4[i4] = mfn = paging_new_log_dirty_node(d);
     unmap_domain_page(l4);
     if ( !mfn_valid(mfn) )
@@ -305,7 +306,7 @@ void paging_mark_pfn_dirty(struct domain
 
     l3 = map_domain_page(mfn);
     mfn = l3[i3];
-    if ( !mfn_valid(mfn) )
+    if ( !mfn_valid(mfn) && dirty )
         l3[i3] = mfn = paging_new_log_dirty_node(d);
     unmap_domain_page(l3);
     if ( !mfn_valid(mfn) )
@@ -313,21 +314,22 @@ void paging_mark_pfn_dirty(struct domain
 
     l2 = map_domain_page(mfn);
     mfn = l2[i2];
-    if ( !mfn_valid(mfn) )
+    if ( !mfn_valid(mfn) && dirty )
         l2[i2] = mfn = paging_new_log_dirty_leaf(d);
     unmap_domain_page(l2);
     if ( !mfn_valid(mfn) )
         goto out;
 
     l1 = map_domain_page(mfn);
-    changed = !__test_and_set_bit(i1, l1);
+    changed = dirty ? !__test_and_set_bit(i1, l1)
+                    : __test_and_clear_bit(i1, l1);
     unmap_domain_page(l1);
     if ( changed )
     {
         PAGING_DEBUG(LOGDIRTY,
-                     "d%d: marked mfn %" PRI_mfn " (pfn %" PRI_pfn ")\n",
-                     d->domain_id, mfn_x(mfn), pfn_x(pfn));
-        d->arch.paging.log_dirty.dirty_count++;
+                     "%pd: marked mfn %" PRI_mfn " (pfn %" PRI_pfn ") %s\n",
+                     d, mfn_x(mfn), pfn_x(pfn), dirty ? "dirty" : "clean");
+        d->arch.paging.log_dirty.dirty_count += dirty ? 1 : -1;
     }
 
 out:
@@ -336,6 +338,16 @@ out:
     return;
 }
 
+void paging_mark_pfn_dirty(struct domain *d, pfn_t pfn)
+{
+    mark_pfn_dirty(d, pfn, true);
+}
+
+void paging_mark_pfn_clean(struct domain *d, pfn_t pfn)
+{
+    mark_pfn_dirty(d, pfn, false);
+}
+
 /* Mark a page as dirty */
 void paging_mark_dirty(struct domain *d, mfn_t gmfn)
 {
@@ -348,7 +360,7 @@ void paging_mark_dirty(struct domain *d,
     /* We /really/ mean PFN here, even for non-translated guests. */
     pfn = _pfn(get_gpfn_from_mfn(mfn_x(gmfn)));
 
-    paging_mark_pfn_dirty(d, pfn);
+    mark_pfn_dirty(d, pfn, true);
 }
 
 
--- a/xen/include/asm-x86/paging.h
+++ b/xen/include/asm-x86/paging.h
@@ -170,8 +170,9 @@ void paging_log_dirty_init(struct domain
 
 /* mark a page as dirty */
 void paging_mark_dirty(struct domain *d, mfn_t gmfn);
-/* mark a page as dirty with taking guest pfn as parameter */
+/* mark a page as dirty/clean with taking guest pfn as parameter */
 void paging_mark_pfn_dirty(struct domain *d, pfn_t pfn);
+void paging_mark_pfn_clean(struct domain *d, pfn_t pfn);
 
 /* is this guest page dirty? 
  * This is called from inside paging code, with the paging lock held. */