x86/mm: Allow a page in p2m_ram_paged_out state to be loaded

This removes the need for a page to be accessed in order to be pageable
again. A pager can now page-in pages at will with no need to map them
in a separate thread.

Signed-off-by: Andres Lagar-Cavilla <andres@lagarcavilla.org>
Acked-by: Tim Deegan <tim@xen.org>
Committed-by: Tim Deegan <tim@xen.org>

diff --git a/xen/arch/x86/mm/p2m.c b/xen/arch/x86/mm/p2m.c
index d90c6deeba92941f93e5f0dde83cc56317fd4b94..e37a1fe0f13fc0437f2eed67327ad6450c7cc10c 100644 (file)
--- a/xen/arch/x86/mm/p2m.c
+++ b/xen/arch/x86/mm/p2m.c
@@ -964,7 +964,7 @@ void p2m_mem_paging_populate(struct domain *d, unsigned long gfn)
 int p2m_mem_paging_prep(struct domain *d, unsigned long gfn, uint64_t buffer)
 {
     struct page_info *page;
-    p2m_type_t p2mt;
+    p2m_type_t p2mt, target_p2mt;
     p2m_access_t a;
     mfn_t mfn;
     struct p2m_domain *p2m = p2m_get_hostp2m(d);
@@ -982,8 +982,8 @@ int p2m_mem_paging_prep(struct domain *d, unsigned long gfn, uint64_t buffer)
     mfn = p2m->get_entry(p2m, gfn, &p2mt, &a, p2m_query, NULL);
 
     ret = -ENOENT;
-    /* Allow only missing pages */
-    if ( p2mt != p2m_ram_paging_in_start )
+    /* Allow missing pages */
+    if ( (p2mt != p2m_ram_paging_in_start) && (p2mt != p2m_ram_paged) )
         goto out;
 
     /* Allocate a page if the gfn does not have one yet */
@@ -1018,8 +1018,15 @@ int p2m_mem_paging_prep(struct domain *d, unsigned long gfn, uint64_t buffer)
         }
     }
 
+    target_p2mt = (p2mt == p2m_ram_paging_in_start) ?
+        /* If we kicked the pager with a populate event, the pager will send
+         * a resume event back */
+        p2m_ram_paging_in :
+        /* If this was called asynchronously by the pager, then we can 
+         * transition directly to the final guest-accessible type */
+        (paging_mode_log_dirty(d) ? p2m_ram_logdirty : p2m_ram_rw);
     /* Fix p2m mapping */
-    set_p2m_entry(p2m, gfn, mfn, PAGE_ORDER_4K, p2m_ram_paging_in, a);
+    set_p2m_entry(p2m, gfn, mfn, PAGE_ORDER_4K, target_p2mt, a);
 
     atomic_dec(&d->paged_pages);