KVM: Support mixed endian machines

Currently kvmtrace is not portable. This will prevent from copying a
trace file from big-endian target to little-endian workstation for analysis.
In the patch, kernel outputs metadata containing a magic number to trace
log, and changes 64-bit words to be u64 instead of a pair of u32s.

Signed-off-by: Tan Li <li.tan@intel.com>
Acked-by: Jerone Young <jyoung5@us.ibm.com>
Acked-by: Hollis Blanchard <hollisb@us.ibm.com>
Signed-off-by: Avi Kivity <avi@qumranet.com>

2 files changed, 14 insertions, 8 deletions

diff --git a/include/linux/kvm.h b/include/linux/kvm.h
index 1c908ac29c6c..0ea064cbfbc8 100644
--- a/include/linux/kvm.h
+++ b/include/linux/kvm.h
@@ -318,14 +318,14 @@ struct kvm_trace_rec {
         __u32 vcpu_id;
         union {
                 struct {
-                        __u32 cycle_lo, cycle_hi;
+                        __u64 cycle_u64;
                         __u32 extra_u32[KVM_TRC_EXTRA_MAX];
                 } cycle;
                 struct {
                         __u32 extra_u32[KVM_TRC_EXTRA_MAX];
                 } nocycle;
         } u;
-};
+} __attribute__((packed));
 
 #define KVMIO 0xAE
 
diff --git a/virt/kvm/kvm_trace.c b/virt/kvm/kvm_trace.c
index 0e495470788d..58141f31ea8f 100644
--- a/virt/kvm/kvm_trace.c
+++ b/virt/kvm/kvm_trace.c
@@ -72,11 +72,7 @@ static void kvm_add_trace(void *probe_private, void *call_data,
         rec.cycle_in    = p->cycle_in;
 
         if (rec.cycle_in) {
-                u64 cycle = 0;
-
-                cycle = get_cycles();
-                rec.u.cycle.cycle_lo = (u32)cycle;
-                rec.u.cycle.cycle_hi = (u32)(cycle >> 32);
+                rec.u.cycle.cycle_u64 = get_cycles();
 
                 for (i = 0; i < rec.extra_u32; i++)
                         rec.u.cycle.extra_u32[i] = va_arg(*args, u32);
@@ -114,8 +110,18 @@ static int kvm_subbuf_start_callback(struct rchan_buf *buf, void *subbuf,
 {
         struct kvm_trace *kt;
 
-        if (!relay_buf_full(buf))
+        if (!relay_buf_full(buf)) {
+                if (!prev_subbuf) {
+                        /*
+                         * executed only once when the channel is opened
+                         * save metadata as first record
+                         */
+                        subbuf_start_reserve(buf, sizeof(u32));
+                        *(u32 *)subbuf = 0x12345678;
+                }
+
                 return 1;
+        }
 
         kt = buf->chan->private_data;
         atomic_inc(&kt->lost_records);