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Commit 37c564f2 authored by Nadav Amit's avatar Nadav Amit Committed by Paolo Bonzini
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KVM: x86: cmpxchg emulation should compare in reverse order 



The current implementation of cmpxchg does not update the flags correctly,
since the accumulator should be compared with the destination and not the other
way around. The current implementation does not update the flags correctly.

Signed-off-by: default avatarNadav Amit <namit@cs.technion.ac.il>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 606b1c3e

arch/x86/kvm/emulate.c

+4 −1
Original line number Diff line number Diff line
@@ -2052,8 +2052,10 @@ static int em_ret_far_imm(struct x86_emulate_ctxt *ctxt) 
static int em_cmpxchg(struct x86_emulate_ctxt *ctxt)

{

	/* Save real source value, then compare EAX against destination. */

	ctxt->dst.orig_val = ctxt->dst.val;

	ctxt->dst.val = reg_read(ctxt, VCPU_REGS_RAX);

	ctxt->src.orig_val = ctxt->src.val;

	ctxt->src.val = reg_read(ctxt, VCPU_REGS_RAX);

	ctxt->src.val = ctxt->dst.orig_val;

	fastop(ctxt, em_cmp);



	if (ctxt->eflags & EFLG_ZF) {
@@ -2063,6 +2065,7 @@ static int em_cmpxchg(struct x86_emulate_ctxt *ctxt) 
		/* Failure: write the value we saw to EAX. */

		ctxt->dst.type = OP_REG;

		ctxt->dst.addr.reg = reg_rmw(ctxt, VCPU_REGS_RAX);

		ctxt->dst.val = ctxt->dst.orig_val;

	}

	return X86EMUL_CONTINUE;

}