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    Subject[PATCH] KVM: x86 emulator: fix debug reg mov instructions
    Date
    More fallout from the writeback fixes: debug register transfer instructions
    do their own writeback and thus need to disable the general writeback
    mechanism. This fixes oopses and some guest failures on AMD machines (the
    Intel variant decodes the instruction in hardware and thus does not need
    emulation).

    Cc: Alistair John Strachan <alistair@devzero.co.uk>
    Signed-off-by: Avi Kivity <avi@qumranet.com>

    diff --git a/drivers/kvm/x86_emulate.c b/drivers/kvm/x86_emulate.c
    index 1f979cb..4b8a0cc 100644
    --- a/drivers/kvm/x86_emulate.c
    +++ b/drivers/kvm/x86_emulate.c
    @@ -1217,11 +1217,13 @@ twobyte_insn:
    }
    break;
    case 0x21: /* mov from dr to reg */
    + no_wb = 1;
    if (modrm_mod != 3)
    goto cannot_emulate;
    rc = emulator_get_dr(ctxt, modrm_reg, &_regs[modrm_rm]);
    break;
    case 0x23: /* mov from reg to dr */
    + no_wb = 1;
    if (modrm_mod != 3)
    goto cannot_emulate;
    rc = emulator_set_dr(ctxt, modrm_reg, _regs[modrm_rm]);
    -
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