From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from eggs.gnu.org ([2001:4830:134:3::10]:35019)
	by lists.gnu.org with esmtp (Exim 4.71)
	(envelope-from <peter.maydell@linaro.org>) id 1ZL79G-00037o-CS
	for qemu-devel@nongnu.org; Fri, 31 Jul 2015 06:02:43 -0400
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <peter.maydell@linaro.org>) id 1ZL79A-000854-5f
	for qemu-devel@nongnu.org; Fri, 31 Jul 2015 06:02:42 -0400
Received: from mail-vk0-f49.google.com ([209.85.213.49]:34859)
	by eggs.gnu.org with esmtp (Exim 4.71)
	(envelope-from <peter.maydell@linaro.org>) id 1ZL79A-00084p-2V
	for qemu-devel@nongnu.org; Fri, 31 Jul 2015 06:02:36 -0400
Received: by vkhg129 with SMTP id g129so19352440vkh.2
	for <qemu-devel@nongnu.org>; Fri, 31 Jul 2015 03:02:35 -0700 (PDT)
MIME-Version: 1.0
In-Reply-To: <CAAhtxhtDQTX-=Gn-ap_O0qJXGC-WeCT83N==WCz65m8OFHDf0A@mail.gmail.com>
References: <CAAhtxhsjYQFqLaVrQ8WCosHiTNmwc7_-=63xuHEpKv1j4VoM=g@mail.gmail.com>
	<CAFEAcA-DDkHxXj03H5JdeKoVivpUJPNx=478D_vLm0wTDbU_mg@mail.gmail.com>
	<878u9xhel1.fsf@linaro.org>
	<CAAhtxhtDQTX-=Gn-ap_O0qJXGC-WeCT83N==WCz65m8OFHDf0A@mail.gmail.com>
From: Peter Maydell <peter.maydell@linaro.org>
Date: Fri, 31 Jul 2015 11:02:16 +0100
Message-ID: <CAFEAcA9BHZOO9Epwx8CCcEgsrvrgyrqCEP-nCf=bmbinqRunMg@mail.gmail.com>
Content-Type: text/plain; charset=UTF-8
Subject: Re: [Qemu-devel] Call Trace for QEMU functions
List-Id: <qemu-devel.nongnu.org>
List-Unsubscribe: <https://lists.nongnu.org/mailman/options/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>
List-Archive: <http://lists.nongnu.org/archive/html/qemu-devel>
List-Post: <mailto:qemu-devel@nongnu.org>
List-Help: <mailto:qemu-devel-request@nongnu.org?subject=help>
List-Subscribe: <https://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
To: Naman patel <naman321@gmail.com>
Cc: =?UTF-8?B?QWxleCBCZW5uw6ll?= <alex.bennee@linaro.org>, QEMU Developers <qemu-devel@nongnu.org>

On 31 July 2015 at 10:29, Naman patel <naman321@gmail.com> wrote:
> Can someone explain me what happens when a guest OS calls "invlpg" on say
> page swap out or a context switch? What exactly is the call flow and how
> QEMU handles this instruction?

When we see the instruction during translation, we emit code
which will
 * get the argument to invlpg (extracting it from the
relevant register, adding any constant offset required for
the addressing mode, etc)
 * make a call to helper_inlvpg().
(target-i386/translate.c has the C code that does this codegen --
search for invlpg)

Later when that generated code is run, we call the helper, which
does what it needs to do (in this case flush a page from QEMU's
TLB cache). When the call returns we'll carry on executing whatever
guest instruction comes next.

> Also is there anyway QEMU can send some data
> back to the guest OS?

INVLPG is just an x86 instruction that performs an operation;
it doesn't modify any registers or flags. So there's no way
for it to tell the guest OS anything.

-- PMM