Commit 900efe20 authored by Nadav Amit's avatar Nadav Amit Committed by Paolo Bonzini
Browse files

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: default avatarNadav Amit <namit@cs.technion.ac.il>
Message-Id: <1427719163-5429-4-git-send-email-namit@cs.technion.ac.il>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 6fd8e127

arch/x86/kvm/emulate.c

+18 −1
Original line number Diff line number Diff line
@@ -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),

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