From 900efe200e317649aecbeaa55619a4fc3adb2251 Mon Sep 17 00:00:00 2001 From: Nadav Amit Date: Mon, 30 Mar 2015 15:39:21 +0300 Subject: [PATCH] KVM: x86: BSF and BSR emulation change register unnecassarily If the source of BSF and BSR is zero, the destination register should not change. That is how real hardware behaves. If we set the destination even with the same value that we had before, we may clear bits [63:32] unnecassarily. Signed-off-by: Nadav Amit Message-Id: <1427719163-5429-4-git-send-email-namit@cs.technion.ac.il> Signed-off-by: Paolo Bonzini --- arch/x86/kvm/emulate.c | 19 ++++++++++++++++++- 1 file changed, 18 insertions(+), 1 deletion(-) diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c index 4961dc5eb303..70045779c725 100644 --- 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), -- 2.39.2