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    Subject[PATCH] KVM: X86: Remove stale values from ctxt->memop before emulation
    When instruction decoding begins there could be stale values
    in the ctxt->memop structure. This causes problems when an
    instruction is emulated with more op-bytes then the guest
    wants (like the bsr instruction which is always emulated
    with 4 or 8 op-bytes).

    The stale value in this structure causes the unit-test for
    the bsrw instruction to fail. Initialize the memop.val with
    0 to prevent such bugs (an alternative fix could be to
    always emulate instructions with the number of op-bytes
    requested by the guest).

    Signed-off-by: Joerg Roedel <>
    arch/x86/kvm/emulate.c | 1 +
    1 file changed, 1 insertion(+)

    diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
    index d4bf50c..1b516ec 100644
    --- a/arch/x86/kvm/emulate.c
    +++ b/arch/x86/kvm/emulate.c
    @@ -3937,6 +3937,7 @@ int x86_decode_insn(struct x86_emulate_ctxt *ctxt, void *insn, int insn_len)
    struct opcode opcode;

    ctxt->memop.type = OP_NONE;
    + ctxt->memop.val = 0;
    ctxt->memopp = NULL;
    ctxt->_eip = ctxt->eip;
    ctxt->fetch.start = ctxt->_eip;

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      Last update: 2012-05-04 18:21    [W:0.026 / U:16.164 seconds]
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