Re: [Xen-devel] [BUGFIX][PATCH 3/4] hvm_save_one: return correct data.

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 15/12/2013 00:29, Don Slutz wrote:

I think I have corrected all coding errors (please check again). And done all requested changes.  I did add the reviewed by (not sure if I should since this changes a large part of the patch, but they are all what Jan said).

I have unit tested it and it appears to work the same as the previous version (as expected).

Here is the new version, also attached.

From e0e8f5246ba492b153884cea93bfe753f1b0782e Mon Sep 17 00:00:00 2001
From: Don Slutz <dslutz@xxxxxxxxxxx>
Date: Tue, 12 Nov 2013 08:22:53 -0500
Subject: [PATCH v2 3/4] hvm_save_one: return correct data.

It is possible that hvm_sr_handlers[typecode].save does not use all
the provided room.  In that case, using:

   instance * hvm_sr_handlers[typecode].size

does not select the correct instance.  Add code to search for the
correct instance.

Signed-off-by: Don Slutz <dslutz@xxxxxxxxxxx>
Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>

but this fairs no better at selecting the correct subset in the case that less data than hvm_sr_handlers[typecode].size is written by hvm_sr_handlers[typecode].save.

It always increments by 'size' bytes, and will only copy the data back if the bytes under desc->instance happen to match the instance we are looking for.

The only solution I can see is that for the per-vcpu records, the save functions get refactored to take an instance ID, and only save their specific instance.

I shall have a go at this and see how invasive it is.

~Andrew

---
 xen/common/hvm/save.c | 28 +++++++++++++++++++++-------
 1 file changed, 21 insertions(+), 7 deletions(-)

diff --git a/xen/common/hvm/save.c b/xen/common/hvm/save.c
index de76ada..6aaea6f 100644
--- a/xen/common/hvm/save.c
+++ b/xen/common/hvm/save.c
@@ -112,13 +112,27 @@ int hvm_save_one(struct domain *d, uint16_t typecode, uint16_t instance,
                d->domain_id, typecode);
         rv = -EFAULT;
     }
-    else if ( copy_to_guest(handle,
-                            ctxt.data
-                            + (instance * hvm_sr_handlers[typecode].size)
-                            + sizeof (struct hvm_save_descriptor),
-                            hvm_sr_handlers[typecode].size
-                            - sizeof (struct hvm_save_descriptor)) )
-        rv = -EFAULT;
+    else
+    {
+        uint32_t off;
+
+        rv = -EBADSLT;
+        for ( off = 0; off < ctxt.cur; off += hvm_sr_handlers[typecode].size )
+        {
+            const struct hvm_save_descriptor *desc = (void *)&ctxt.data[off];
+
+            if ( instance == desc->instance )
+            {
+                rv = 0;
+                if ( copy_to_guest(handle,
+                                   ctxt.data + off + sizeof(*desc),
+                                   hvm_sr_handlers[typecode].size
+                                   - sizeof(*desc)) )
+                    rv = -EFAULT;
+                break;
+            }
+        }
+    }

     xfree(ctxt.data);
     return rv;

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