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    Subject[PATCH 40/50] KVM: Support mixed endian machines
    Date
    From: Tan, Li <li.tan@intel.com>

    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>
    ---
    include/linux/kvm.h | 4 ++--
    virt/kvm/kvm_trace.c | 18 ++++++++++++------
    2 files changed, 14 insertions(+), 8 deletions(-)

    diff --git a/include/linux/kvm.h b/include/linux/kvm.h
    index 1c908ac..0ea064c 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 0e49547..58141f3 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);
    --
    1.5.6


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