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>

diff --git a/include/linux/kvm.h b/include/linux/kvm.h
index 1c908ac29c6c3287c2d0934ea1ca4a691dfce982..0ea064cbfbc8660a7119a22546165ca3ec3387cd 100644 (file)
--- 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 0e495470788da6b83061e2f9c6192ec76b809fb2..58141f31ea8fb218f8091b16f192857615ad66b6 100644 (file)
--- 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);