[Xen-devel] [PATCH] Fix check of XENOPROF_get_buffer and XENOPROF_set_passive argument max_samples

[Markus Armbruster <armbru@xxxxxxxxxx>]

Fix code limiting XENOPROF_get_buffer and XENOPROF_set_passive
argument max_samples so that no more than MAX_OPROF_SHARED_PAGES are
used.

Signed-off-by: Markus Armbruster <armbru@xxxxxxxxxx>
---
A few quick tests comparing old to new code:

                     old code                new code
    arg         checked     npages      checked     npages
    0           0           1           0           1
    1           1           1           1           1
    5457        5457        32          5457        32
    5458        5457        32          5457        32
    2000000000  2000000000  184415      5457        32
    2147483647  2147483647  1           5457        32
    -1          -1          1           5457        32


diff -r efea4c3b8bcc xen/arch/x86/oprofile/xenoprof.c
--- a/xen/arch/x86/oprofile/xenoprof.c  Fri Oct 13 17:10:27 2006 +0100
+++ b/xen/arch/x86/oprofile/xenoprof.c  Fri Oct 13 19:44:01 2006 +0200
@@ -122,6 +122,7 @@ int alloc_xenoprof_struct(struct domain 
 {
     struct vcpu *v;
     int nvcpu, npages, bufsize, max_bufsize;
+    unsigned max_max_samples;
     int i;
 
     d->xenoprof = xmalloc(struct xenoprof);
@@ -139,17 +140,15 @@ int alloc_xenoprof_struct(struct domain 
     for_each_vcpu ( d, v )
         nvcpu++;
 
-    /* reduce buffer size if necessary to limit pages allocated */
+    /* reduce max_samples if necessary to limit pages allocated */
+    max_bufsize = (MAX_OPROF_SHARED_PAGES * PAGE_SIZE) / nvcpu;
+    max_max_samples = ( (max_bufsize - sizeof(struct xenoprof_buf)) /
+                        sizeof(struct event_log) ) + 1;
+    if ( (unsigned)max_samples > max_max_samples )
+        max_samples = max_max_samples;
+
     bufsize = sizeof(struct xenoprof_buf) +
         (max_samples - 1) * sizeof(struct event_log);
-    max_bufsize = (MAX_OPROF_SHARED_PAGES * PAGE_SIZE) / nvcpu;
-    if ( bufsize > max_bufsize )
-    {
-        bufsize = max_bufsize;
-        max_samples = ( (max_bufsize - sizeof(struct xenoprof_buf)) /
-                        sizeof(struct event_log) ) + 1;
-    }
-
     npages = (nvcpu * bufsize - 1) / PAGE_SIZE + 1;
     
     d->xenoprof->rawbuf = alloc_xenoprof_buf(is_passive ? dom0 : d, npages);

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