[Xen-devel] [PATCH v2 2/2] xentrace: handle sparse cpu ids correctly in xen trace buffer handling

[Juergen Gross <jgross@xxxxxxxx>]

The per-cpu buffers for Xentrace are addressed by cpu-id, but the info
array for the buffers is sized only by number of online cpus. This
might lead to crashes when using Xentrace with smt=0.

The t_info structure has to be sized based on nr_cpu_ids.

Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
---
 tools/xentrace/xentrace.c | 2 +-
 xen/common/trace.c        | 6 +++---
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/tools/xentrace/xentrace.c b/tools/xentrace/xentrace.c
index 590a91e091..12497a16b4 100644
--- a/tools/xentrace/xentrace.c
+++ b/tools/xentrace/xentrace.c
@@ -596,7 +596,7 @@ static unsigned int get_num_cpus(void)
         exit(EXIT_FAILURE);
     }
 
-    return physinfo.nr_cpus;
+    return physinfo.max_cpu_id + 1;
 }
 
 /**
diff --git a/xen/common/trace.c b/xen/common/trace.c
index 8cdc17b731..c079454c6a 100644
--- a/xen/common/trace.c
+++ b/xen/common/trace.c
@@ -113,7 +113,7 @@ static int calculate_tbuf_size(unsigned int pages, uint16_t 
t_info_first_offset)
     struct t_info dummy_pages;
     typeof(dummy_pages.tbuf_size) max_pages;
     typeof(dummy_pages.mfn_offset[0]) max_mfn_offset;
-    unsigned int max_cpus = num_online_cpus();
+    unsigned int max_cpus = nr_cpu_ids;
     unsigned int t_info_words;
 
     /* force maximum value for an unsigned type */
@@ -151,11 +151,11 @@ static int calculate_tbuf_size(unsigned int pages, 
uint16_t t_info_first_offset)
      * NB this calculation is correct, because t_info_first_offset is
      * in words, not bytes, not bytes
      */
-    t_info_words = num_online_cpus() * pages + t_info_first_offset;
+    t_info_words = nr_cpu_ids * pages + t_info_first_offset;
     t_info_pages = PFN_UP(t_info_words * sizeof(uint32_t));
     printk(XENLOG_INFO "xentrace: requesting %u t_info pages "
            "for %u trace pages on %u cpus\n",
-           t_info_pages, pages, num_online_cpus());
+           t_info_pages, pages, nr_cpu_ids);
     return pages;
 }
 
-- 
2.16.4


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