[Xen-devel] [PATCH RFC v2 2/3] xen/shadow: fix shadow_track_dirty_vram to work on hvm guests

[Roger Pau Monne <roger.pau@xxxxxxxxxx>]

Modify shadow_track_dirty_vram to use a local buffer and then flush to the
guest without the paging_lock held. This is modeled after
hap_track_dirty_vram.

Signed-off-by: Roger Pau Monnà <roger.pau@xxxxxxxxxx>
Cc: Tim Deegan <tim@xxxxxxx>
Cc: Jan Beulich <jbeulich@xxxxxxxx>
Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
 xen/arch/x86/mm/shadow/common.c | 18 +++++++++++++++---
 1 file changed, 15 insertions(+), 3 deletions(-)

diff --git a/xen/arch/x86/mm/shadow/common.c b/xen/arch/x86/mm/shadow/common.c
index 2e43d6d..8fff43a 100644
--- a/xen/arch/x86/mm/shadow/common.c
+++ b/xen/arch/x86/mm/shadow/common.c
@@ -3516,7 +3516,7 @@ static void sh_clean_dirty_bitmap(struct domain *d)
 int shadow_track_dirty_vram(struct domain *d,
                             unsigned long begin_pfn,
                             unsigned long nr,
-                            XEN_GUEST_HANDLE_64(uint8) dirty_bitmap)
+                            XEN_GUEST_HANDLE_64(uint8) guest_dirty_bitmap)
 {
     int rc;
     unsigned long end_pfn = begin_pfn + nr;
@@ -3526,6 +3526,7 @@ int shadow_track_dirty_vram(struct domain *d,
     p2m_type_t t;
     struct sh_dirty_vram *dirty_vram;
     struct p2m_domain *p2m = p2m_get_hostp2m(d);
+    uint8_t *dirty_bitmap = NULL;
 
     if ( end_pfn < begin_pfn || end_pfn > p2m->max_mapped_pfn + 1 )
         return -EINVAL;
@@ -3554,6 +3555,12 @@ int shadow_track_dirty_vram(struct domain *d,
         goto out;
     }
 
+    dirty_bitmap = xzalloc_bytes(dirty_size);
+    if ( dirty_bitmap == NULL )
+    {
+        rc = -ENOMEM;
+        goto out;
+    }
     /* This should happen seldomly (Video mode change),
      * no need to be careful. */
     if ( !dirty_vram )
@@ -3587,7 +3594,7 @@ int shadow_track_dirty_vram(struct domain *d,
     {
         /* still completely clean, just copy our empty bitmap */
         rc = -EFAULT;
-        if ( copy_to_guest(dirty_bitmap, dirty_vram->dirty_bitmap, dirty_size) 
== 0 )
+        if ( memcpy(dirty_bitmap, dirty_vram->dirty_bitmap, dirty_size) != 
NULL )
             rc = 0;
     }
     else
@@ -3669,7 +3676,8 @@ int shadow_track_dirty_vram(struct domain *d,
             sh_unmap_domain_page(map_sl1p);
 
         rc = -EFAULT;
-        if ( copy_to_guest(dirty_bitmap, dirty_vram->dirty_bitmap, dirty_size) 
== 0 ) {
+        if ( memcpy(dirty_bitmap, dirty_vram->dirty_bitmap, dirty_size) != 
NULL )
+        {
             memset(dirty_vram->dirty_bitmap, 0, dirty_size);
             if (dirty_vram->last_dirty + SECONDS(2) < NOW())
             {
@@ -3697,6 +3705,10 @@ out_dirty_vram:
 
 out:
     paging_unlock(d);
+    if ( rc == 0 && dirty_bitmap != NULL )
+        if ( copy_to_guest(guest_dirty_bitmap, dirty_bitmap, dirty_size) != 0 )
+            rc = -EFAULT;
+    xfree(dirty_bitmap);
     p2m_unlock(p2m_get_hostp2m(d));
     return rc;
 }
-- 
1.9.5 (Apple Git-50.3)


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