From: Tim Deegan <Tim.Deegan@citrix.com>
Date: Thu, 13 Jan 2011 15:46:13 +0000 (+0000)
Subject: x86/mm: make page-sharing use the proper typecount functions
X-Git-Tag: archive/raspbian/4.8.0-1+rpi1~1^2~10922
X-Git-Url: https://dgit.raspbian.org/%22http:/www.example.com/cgi/%22https://%22%22/%22http:/www.example.com/cgi/%22https:/%22%22?a=commitdiff_plain;h=4e985437cc86d73a4a0db5764497ee4799c26b0d;p=xen.git

x86/mm: make page-sharing use the proper typecount functions
instead of having its own cmpxchg loops.

This should remove some confusion about the use of PGT_none,
and also makes page-sharing participate properly in the TLB
flushing discipline.

Signed-off-by: Tim Deegan <Tim.Deegan@citrix.com>
---

diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c
index 2b728aa390..c1666d7504 100644
--- a/xen/arch/x86/mm.c
+++ b/xen/arch/x86/mm.c
@@ -2367,7 +2367,7 @@ static int __get_page_type(struct page_info *page, unsigned long type,
 
                 /* No special validation needed for writable pages. */
                 /* Page tables and GDT/LDT need to be scanned for validity. */
-                if ( type == PGT_writable_page )
+                if ( type == PGT_writable_page || type == PGT_shared_page )
                     nx |= PGT_validated;
             }
         }
@@ -4167,32 +4167,25 @@ int page_make_sharable(struct domain *d,
                        struct page_info *page, 
                        int expected_refcnt)
 {
-    unsigned long x, nx, y;
-
-    /* Acquire ref first, so that the page doesn't dissapear from us */
-    if(!get_page(page, d))
-        return -EINVAL;
-
     spin_lock(&d->page_alloc_lock);
 
     /* Change page type and count atomically */
-    y = page->u.inuse.type_info;
-    nx = PGT_shared_page | PGT_validated | 1; 
-    do {
-        x = y;
-        /* We can only change the type if count is zero, and 
-           type is PGT_none */
-        if((x & (PGT_type_mask | PGT_count_mask)) != PGT_none)
-        {
-            put_page(page);
-            spin_unlock(&d->page_alloc_lock);
-            return -EEXIST;
-        }
-        y = cmpxchg(&page->u.inuse.type_info, x, nx);
-    } while(x != y);
+    if ( !get_page_and_type(page, d, PGT_shared_page) )
+    {
+        spin_unlock(&d->page_alloc_lock);
+        return -EINVAL;
+    }
+
+    /* Check it wasn't already sharable and undo if it was */
+    if ( (page->u.inuse.type_info & PGT_count_mask) != 1 )
+    {
+        put_page_and_type(page);
+        spin_unlock(&d->page_alloc_lock);
+        return -EEXIST;
+    }
 
-    /* Check if the ref count is 2. The first from PGT_allocated, and the second
-     * from get_page at the top of this function */
+    /* Check if the ref count is 2. The first from PGT_allocated, and
+     * the second from get_page_and_type at the top of this function */
     if(page->count_info != (PGC_allocated | (2 + expected_refcnt)))
     {
         /* Return type count back to zero */
@@ -4205,39 +4198,27 @@ int page_make_sharable(struct domain *d,
     d->tot_pages--;
     page_list_del(page, &d->page_list);
     spin_unlock(&d->page_alloc_lock);
-
-    /* NOTE: We are not putting the page back. In effect this function acquires
-     * one ref and type ref for the caller */
-
     return 0;
 }
 
 int page_make_private(struct domain *d, struct page_info *page)
 {
-    unsigned long x, y;
-
     if(!get_page(page, dom_cow))
         return -EINVAL;
     
     spin_lock(&d->page_alloc_lock);
 
-    /* Change page type and count atomically */
-    y = page->u.inuse.type_info;
-    do {
-        x = y;
-        /* We can only change the type if count is one */
-        if((x & (PGT_type_mask | PGT_count_mask)) != 
-                (PGT_shared_page | 1))
-        {
-            put_page(page);
-            spin_unlock(&d->page_alloc_lock);
-            return -EEXIST;
-        }
-        y = cmpxchg(&page->u.inuse.type_info, x, PGT_none);
-    } while(x != y);
+    /* We can only change the type if count is one */
+    if ( (page->u.inuse.type_info & (PGT_type_mask | PGT_count_mask))
+         != (PGT_shared_page | 1) )
+    {
+        put_page(page);
+        spin_unlock(&d->page_alloc_lock);
+        return -EEXIST;
+    }
 
-    /* We dropped type ref above, drop one ref count too */
-    put_page(page);
+    /* Drop the final typecount */
+    put_page_and_type(page);
 
     /* Change the owner */
     ASSERT(page_get_owner(page) == dom_cow);