[Xen-devel] [PATCH RFC] x86/HVM: meet xentrace's expectations on emulation event data

["Jan Beulich" <JBeulich@xxxxxxxx>]

According to the logic in hvm_mmio_assist_process(), 64 bits of data are
expected with 64-bit addresses, and 32 bits of data with 32-bit ones. I
don't think this is very reasonable, but I'm also not going to touch the
consumer side, the more that it is anyway not very helpful for the code
here to only ever supply 32 bits of data (despite the field being 64
bits wide, and having been even in the 32-bit days of Xen).

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
RFC: Untested; solely based on the observation of "(no data)" in a trace
     where it was entirely unclear why no data would have been available.
     I just so happened that the guest had more than 4Gb of memory, and
     hence addresses were not representable as 32-bit values.

--- a/xen/arch/x86/hvm/emulate.c
+++ b/xen/arch/x86/hvm/emulate.c
@@ -30,7 +30,7 @@ struct hvmemul_cache
 static void hvmtrace_io_assist(const ioreq_t *p)
 {
     unsigned int size, event;
-    unsigned char buffer[12];
+    unsigned char buffer[16];
 
     if ( likely(!tb_init_done) )
         return;
@@ -47,8 +47,11 @@ static void hvmtrace_io_assist(const ior
 
     if ( !p->data_is_ptr )
     {
-        *(uint32_t *)&buffer[size] = p->data;
-        size += 4;
+        if ( size == 4 )
+            *(uint32_t *)&buffer[size] = p->data;
+        else
+            *(uint64_t *)&buffer[size] = p->data;
+        size *= 2;
     }
 
     trace_var(event, 0/*!cycles*/, size, buffer);





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