KVM: x86: BSF and BSR emulation change register unnecassarily

[karo-tx-linux.git] / arch / x86 / kvm / emulate.c

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 4961dc5eb303744a7c5af9b571f99b86e16f3070..70045779c72503757899bed6890d9903fc97d699 100644 (file)
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -962,6 +962,22 @@ FASTOP2(xadd);
 
 FASTOP2R(cmp, cmp_r);
 
+static int em_bsf_c(struct x86_emulate_ctxt *ctxt)
+{
+       /* If src is zero, do not writeback, but update flags */
+       if (ctxt->src.val == 0)
+               ctxt->dst.type = OP_NONE;
+       return fastop(ctxt, em_bsf);
+}
+
+static int em_bsr_c(struct x86_emulate_ctxt *ctxt)
+{
+       /* If src is zero, do not writeback, but update flags */
+       if (ctxt->src.val == 0)
+               ctxt->dst.type = OP_NONE;
+       return fastop(ctxt, em_bsr);
+}
+
 static u8 test_cc(unsigned int condition, unsigned long flags)
 {
        u8 rc;
@@ -4188,7 +4204,8 @@ static const struct opcode twobyte_table[256] = {
        N, N,
        G(BitOp, group8),
        F(DstMem | SrcReg | ModRM | BitOp | Lock | PageTable, em_btc),
-       F(DstReg | SrcMem | ModRM, em_bsf), F(DstReg | SrcMem | ModRM, em_bsr),
+       I(DstReg | SrcMem | ModRM, em_bsf_c),
+       I(DstReg | SrcMem | ModRM, em_bsr_c),
        D(DstReg | SrcMem8 | ModRM | Mov), D(DstReg | SrcMem16 | ModRM | Mov),
        /* 0xC0 - 0xC7 */
        F2bv(DstMem | SrcReg | ModRM | SrcWrite | Lock, em_xadd),