Re: move hyperv CHANNELMSG_UNLOAD from crashed kernel to kdump kernel

Path	csiph.com!1.us.feeder.erje.net!2.us.feeder.erje.net!feeder.erje.net!2.eu.feeder.erje.net!news2.arglkargh.de!news.mixmin.net!aioe.org!bofh.it!news.nic.it!robomod
From	Olaf Hering <olaf@aepfle.de>
Newsgroups	linux.kernel
Subject	Re: move hyperv CHANNELMSG_UNLOAD from crashed kernel to kdump kernel
Date	Thu, 15 Dec 2016 11:40:02 +0100
Message-ID	<sOBC9-4DI-9@gated-at.bofh.it> (permalink)
References	<sLGf0-6eS-33@gated-at.bofh.it> <sOBC9-4DI-1@gated-at.bofh.it>
X-Original-To	Vitaly Kuznetsov <vkuznets@redhat.com>
Dkim-Signature	v=1; a=rsa-sha256; c=relaxed/relaxed; t=1481798226; l=1586; s=domk; d=aepfle.de; h=In-Reply-To:Content-Disposition:Content-Type:MIME-Version: References:Subject:Cc:To:From:Date; bh=yI+iiXGkdVGNU+vPcGd+4RawgOTYCpM5RqChd9EzwVA=; b=lsr9tzyc0H0njPrGBf6LhL2HVZgiptI2RFSQ9rzTAWzJlJqbuuMZSAMP2Ld5ndrxjK jnvPmdMZMTITUNhwI2yqJRWvi9D/7sayRGh8syqtPTwOvOWyyVCTBNomK/A5aEAOvLIN RWExin82PqxAS4q/XC1aQEFPzIKhzyZWS5DQo=
X-Rzg-Auth	:P2EQZWCpfu+qG7CngxMFH1J+yackYocTD1iAi8x+OWi5z/J1IL7CYRxLEwpkY2XtLzyRUcY=
X-Rzg-Class-ID	mo00
MIME-Version	1.0
Content-Type	multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="qMm9M+Fa2AknHoGS"
Content-Disposition	inline
User-Agent	Mutt/1.7.2 (6888)
Sender	robomod@news.nic.it
List-ID	<linux-kernel.vger.kernel.org>
X-Mailing-List	linux-kernel@vger.kernel.org
Approved	robomod@news.nic.it
Lines	46
Organization	linux.* mail to news gateway
X-Original-Cc	kys@microsoft.com, gregkh@linuxfoundation.org, linux-kernel@vger.kernel.org, devel@linuxdriverproject.org
X-Original-Date	Thu, 15 Dec 2016 11:34:03 +0100
X-Original-Message-ID	<20161215103402.GA6336@aepfle.de>
X-Original-References	<20161207085110.GC1618@aepfle.de> <87r3594hef.fsf@vitty.brq.redhat.com>
X-Original-Sender	linux-kernel-owner@vger.kernel.org
Xref	csiph.com linux.kernel:1542624

Show key headers only | View raw

[Multipart message — attachments visible in raw view] - view raw

On Thu, Dec 15, Vitaly Kuznetsov wrote:

> I see a number of minor but at least one major issue against such move:
> At least for some Hyper-V versions (2012R2 for example)
> CHANNELMSG_UNLOAD_RESPONSE is delivered to the CPU which initially sent 
> CHANNELMSG_REQUESTOFFERS and on kdump we may not have this CPU up as
> we usually do kdump with nr_cpus=1 (and on the CPU which crashed). 

Since the kdump or kexec kernel will send the unload during boot I would
expect the response to arrive where it was sent, independent from the
number of cpus.

> Minor issue is the necessity preserve the information about
> message/events pages across kexec.

I guess this info is stored somewhere, and the relevant gfns can be
preserved across kernels, if we try really hard.

But after looking further at the involved code paths it seems that the
implemnted polling might be good enough to snatch the response. Was the
mdelay(10) just an arbitrary decision? I interpret the comments in
vmbus_signal_eom such that the host may overwrite the response. Perhaps
such thing may happen during the mdelay?

Olaf

Thread

Re: move hyperv CHANNELMSG_UNLOAD from crashed kernel to kdump kernel Vitaly Kuznetsov <vkuznets@redhat.com> - 2016-12-15 11:40 +0100
  Re: move hyperv CHANNELMSG_UNLOAD from crashed kernel to kdump kernel Olaf Hering <olaf@aepfle.de> - 2016-12-15 11:40 +0100
    Re: move hyperv CHANNELMSG_UNLOAD from crashed kernel to kdump kernel Olaf Hering <olaf@aepfle.de> - 2016-12-15 11:40 +0100
      Re: move hyperv CHANNELMSG_UNLOAD from crashed kernel to kdump kernel Vitaly Kuznetsov <vkuznets@redhat.com> - 2016-12-15 12:00 +0100
    Re: move hyperv CHANNELMSG_UNLOAD from crashed kernel to kdump kernel Vitaly Kuznetsov <vkuznets@redhat.com> - 2016-12-15 12:00 +0100
      Re: move hyperv CHANNELMSG_UNLOAD from crashed kernel to kdump kernel Olaf Hering <olaf@aepfle.de> - 2016-12-15 14:00 +0100
        Re: move hyperv CHANNELMSG_UNLOAD from crashed kernel to kdump kernel Vitaly Kuznetsov <vkuznets@redhat.com> - 2016-12-15 14:30 +0100
          Re: move hyperv CHANNELMSG_UNLOAD from crashed kernel to kdump kernel Olaf Hering <olaf@aepfle.de> - 2016-12-15 15:00 +0100
            Re: move hyperv CHANNELMSG_UNLOAD from crashed kernel to kdump kernel Vitaly Kuznetsov <vkuznets@redhat.com> - 2016-12-15 15:40 +0100
              RE: move hyperv CHANNELMSG_UNLOAD from crashed kernel to kdump kernel KY Srinivasan <kys@microsoft.com> - 2016-12-16 02:00 +0100
          Re: move hyperv CHANNELMSG_UNLOAD from crashed kernel to kdump kernel Olaf Hering <olaf@aepfle.de> - 2016-12-15 16:20 +0100

csiph-web