From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Serge E. Hallyn" <serge@hallyn.com>
Subject: Re: buggy emulate_int_real
Date: Tue, 12 Apr 2011 02:53:19 -0500
Message-ID: <20110412075319.GA28696@hallyn.com>
References: <20110408210900.GA26787@hallyn.com>
 <4DA16AA1.7010108@redhat.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Cc: KVM mailing list <kvm@vger.kernel.org>
To: Avi Kivity <avi@redhat.com>
Return-path: <kvm-owner@vger.kernel.org>
Received: from hrndva-omtalb.mail.rr.com ([71.74.56.124]:51851 "EHLO
	hrndva-omtalb.mail.rr.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1752268Ab1DLHxU (ORCPT <rfc822;kvm@vger.kernel.org>);
	Tue, 12 Apr 2011 03:53:20 -0400
Content-Disposition: inline
In-Reply-To: <4DA16AA1.7010108@redhat.com>
Sender: kvm-owner@vger.kernel.org
List-ID: <kvm.vger.kernel.org>

Quoting Avi Kivity (avi@redhat.com):
> On 04/09/2011 12:09 AM, Serge E. Hallyn wrote:
> >Hi,
> >
> >at https://bugs.launchpad.net/ubuntu/+source/qemu-kvm/+bug/747090, it was
> >found that emulate_int_real() sometimes pushes the wrong eip when doing a
> >int.  Whereas with non-kvm qemu we push the next instruction after the
> >int, with kvm we push the addr of the instruction itself.
> >
> 
> 
> The code says:
> 
>     c->src.val = c->eip;
>     emulate_push(ctxt, ops);
>     rc = writeback(ctxt, ops);
>     if (rc != X86EMUL_CONTINUE)
>         return rc;
> 
> which appears to be the address of the next instruction from my
> reading of the code (see how insn_fetch() increments c->eip).

Nevertheless removing commits

	a92601bb707f6f49fd5563ef3d09928e70cc222e
	63995653ade16deacaea5b49ceaf6376314593ac
	6e154e56b4d7a6a28c54f0984e13d3f8defc4755

changes the eip value being pushed.  If you look at 
a92601bb707f6f49fd5563ef3d09928e70cc222e, you see:

        if (vmx->rmode.vm86_active) {
-               vmx->rmode.irq.pending = true;
-               vmx->rmode.irq.vector = nr;
-               vmx->rmode.irq.rip = kvm_rip_read(vcpu);
-               if (kvm_exception_is_soft(nr))
-                       vmx->rmode.irq.rip +=
-                               vmx->vcpu.arch.event_exit_inst_len;
-               intr_info |= INTR_TYPE_SOFT_INTR;
-               vmcs_write32(VM_ENTRY_INTR_INFO_FIELD, intr_info);
-               vmcs_write32(VM_ENTRY_INSTRUCTION_LEN, 1);
-               kvm_rip_write(vcpu, vmx->rmode.irq.rip - 1);
+               if (kvm_inject_realmode_interrupt(vcpu, nr) != EMULATE_DONE)
+                       kvm_make_request(KVM_REQ_TRIPLE_FAULT, vcpu);
                return;
        }

but kvm_inject_realmode_interrupt() does not appear to increment
vmx->rmode.irq.rip anywhere, as the code being replaced does.

-serge