Re: [win-pv-devel] Porting libvchan to use the Windows PV Drivers

[RafaÅ WojdyÅa <omeg@xxxxxxxxxxxxxxxxxxxxxx>]

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On 12.03.2015 18:09, Paul Durrant wrote:
>> -----Original Message----- From:
>> win-pv-devel-bounces@xxxxxxxxxxxxxxxxxxxx [mailto:win-pv-devel-
>> bounces@xxxxxxxxxxxxxxxxxxxx] On Behalf Of Rafal Wojdyla Sent: 12
>> March 2015 17:06 To: Paul Durrant;
>> win-pv-devel@xxxxxxxxxxxxxxxxxxxx Cc: Marek Marczykowski-GÃrecki
>> Subject: Re: [win-pv-devel] Porting libvchan to use the Windows
>> PV Drivers
>>
> On 2015-03-12 17:45, Paul Durrant wrote:
>>>>> -----Original Message----- From: RafaÅ WojdyÅa
>>>>> [mailto:omeg@xxxxxxxxxxxxxxxxxxxxxx] Sent: 12 March 2015
>>>>> 16:17 To: Paul Durrant; win-pv-devel@xxxxxxxxxxxxxxxxxxxx
>>>>> Subject: Re: [win-pv-devel] Porting libvchan to use the
>>>>> Windows PV Drivers
>>>>>
>>>> On 2015-03-11 18:46, Paul Durrant wrote:
>>>>>>>> -----Original Message----- From:
>>>>>>>> win-pv-devel-bounces@xxxxxxxxxxxxxxxxxxxx
>>>>>>>> [mailto:win-pv-devel- bounces@xxxxxxxxxxxxxxxxxxxx]
>>>>>>>> On Behalf Of Rafal Wojdyla Sent: 10 March 2015 20:16
>>>>>>>> To: win-pv-devel@xxxxxxxxxxxxxxxxxxxx Subject: Re:
>>>>>>>> [win-pv-devel] Porting libvchan to use the Windows
>>>>>>>> PV Drivers
>>>>>>>>
>>>>>>> Hi,
>>>>>>>
>>>>>>>
>>>>>>>> Hi,
>>>>>>>
>>>>>>> I'm unable to properly reply to the thread since I
>>>>>>> just subscribed to this list but I figured it's worth
>>>>>>> chiming in (last message is here:
>>>>>>> http://lists.xenproject.org/archives/html/win-pv-devel/2015-01/msg0
>
>>>>>>>
006
>>>>
>>>>>>>
> 0.
>>>>>>>
>>>>>>>
>>>> html)
>>>>>>>
>>>>>>>
>>>>>>>> Yes, I understand; I just saw your subscription
>>>>>>>> message :-)
>>>>>>>
>>>>>>> First, some background about me. I'm currently the main
>>>>>>> and pretty much the only developer/maintainer of guest
>>>>>>> tools for Windows for Qubes OS
>>>>>>> (https://wiki.qubes-os.org/). Some of you may have
>>>>>>> heard of Qubes -- in short, it's an attempt at creating
>>>>>>> a secure OS based on lightweight AppVMs, currently
>>>>>>> using Linux/Xen as base. It supports Windows HVMs and
>>>>>>> our guest tools provide integration with dom0/other
>>>>>>> domUs (services like data transfer, remote execution,
>>>>>>> seamless GUI experience etc).
>>>>>>>
>>>>>>>
>>>>>>>> Cool.
>>>>>>>
>>>>>>> We're in the process of finalizing the next major
>>>>>>> release (r3) of Qubes, it will use Xen 4.4 instead of
>>>>>>> r2's Xen 4.1. As for our Windows tools, they are
>>>>>>> (currently) using PV drivers based on James Harper's
>>>>>>> cod e.
>>>>>>>
>>>>>>> Our inter-VM communication protocol uses vchan (in
>>>>>>> fact, vchan originates from our patch accepted into
>>>>>>> Xen's source a few years ago). In Qubes r2 we have a
>>>>>>> Windows libvchan implementation, but as stated above,
>>>>>>> it uses old PV drivers interfaces. You can find it
>>>>>>> here: https://github.com/QubesOS/qubes-core-vchan-xen
>>>>>>>
>>>>>>> That implementation has one big flaw: client side
>>>>>>> vchan functions are not implemented. It didn't matter
>>>>>>> for Qubes r2, where all vchan communication is passing
>>>>>>> through dom0 anyway. In Qubes r3 however, we need that
>>>>>>> working because of redesigned inter-VM communication
>>>>>>> protocol that allows direct VM-VM communication after
>>>>>>> dom0 arbitration.
>>>>>>>
>>>>>>> Unfortunately Harper's drivers don't seem to implement
>>>>>>> the needed kernel interfaces for that as well.
>>>>>>>
>>>>>>>> I assume you mean grant mapping? Or maybe just grant
>>>>>>>> copy, since that would be safer?
>>>>>>>
>>>>>>> I didn't need to look into PV drivers sources before,
>>>>>>> but it seems I will need to do that now :) I found the
>>>>>>> new PV drivers and this mailing list, found the thread
>>>>>>> about vchan implementation... and that's pretty much it
>>>>>>> for now.
>>>>>>>
>>>>>>> As I said, I don't have much experience in Xen APIs
>>>>>>> (didn't need to tinker with them directly before). I
>>>>>>> do, however, have extensive WinAPI knowledge and
>>>>>>> moderate amount of Windows driver development
>>>>>>> experience (part of our guest tools is a custom display
>>>>>>> driver that allows no-copy video memory sharing with
>>>>>>> dom0). I managed to build the new drivers and will test
>>>>>>> them on our dev Qubes build soon.
>>>>>>>
>>>>>>> So, to summarize, I'm very interested in developing a
>>>>>>> Windows vchan implementation on top of the new PV
>>>>>>> drivers. I'll be reading through the driver sources for
>>>>>>> a bit still to familiarize myself with the environment.
>>>>>>> If anyone managed to get something working, or just has
>>>>>>> ideas, let me know.
>>>>>>>
>>>>>>>
>>>>>>>> If you want to look at adding the necessary code to
>>>>>>>> the XENBUS_GNTTAB interface to do grant map/copy then
>>>>>>>> I don't imagine it will be too hard. Adding support
>>>>>>>> for copy would be easiest but it would also be
>>>>>>>> possible to grant map pages into the platform PCI
>>>>>>>> device's BAR (which is where the shared info page and
>>>>>>>> the grant table itself live).
>>>>>>>
>>>>>>>> Let me know if have any specific questions or need
>>>>>>>> some help getting the drivers going in your
>>>>>>>> environment.
>>>>>>>
>>>> I've tested the drivers on a Win7 pro x64 HVM on Qubes r2 (r3
>>>> is still a bit unstable). Xenbus and xeniface both install
>>>> fine. Xenvbd installs OK but the OS BSODs on reboot with code
>>>> 7B (inaccessible boot device). I'll try to pinpoint the exact
>>>> failure spot once I setup the pvdrivers sources inside my
>>>> development VM.
>>>>
>>>>
>>>>> 0x7B can occur in many circumstances. The drivers do log
>>>>> quite a bit of info, particularly in checked builds, so
>>>>> there'll probably be something there to indicate the exact
>>>>> nature of the failure. The main informational logging
>>>>> (which is the same for free or checked builds) is written
>>>>> to the qemu logging port (0x12) and debug logging (checked
>>>>> build only) goes to the Xen port (0xE9). If you watch
>>>>> wherever you have those redirected then you may be able to
>>>>> spot the problem. If you can't then post them to the list
>>>>> and I'll take a look.
>>>>
>>>> Do the drivers have specific requirements for backend
>>>> (Xen/Qemu version)? We're not really using Qemu in dom0, only
>>>> in minimal stubdoms for HVMs, so that may be a problem.
>>>>
>>>>
>>>>> That's not usually a problem. Do you have PV backends for
>>>>> disk and net set up though? The fact that you got a 0x7B
>>>>> after installing xenvbd may simply mean that your toolstack
>>>>> has just not set up a PV backend.
> We do have backends set up (xen-blkback for vbd). I'll check in
> dom0 whether it crashes after the device gets attached or before.
>
>
>> Ok. I must admit that I tend to use qdisk as a backend in most of
>> my testing, but blkback should be fine. I'll sanity check it
>> myself when I get time though.
>
Sometimes the VM BSODs with 0x7E. I managed to connect WinDbg to it
and grab some logs (in the attachment). At a glance it seems like a
lot of event channel failures...

XENVBD|PdoReset:ASSERTION FAILED: (((NTSTATUS)(Status)) >= 0)
Assertion
f:\qubes-builder\qubes-src\xen-pv\xenvbd\src\xenvbd\pdo.c(2297):
(((NTSTATUS)(Status)) >= 0)


> Also adding Marek to the conversation, he's one of our core
> architects and knows more about backend stuff than I do :)
>
>
>> Cool.
>
>> Paul
>
>>>>
>>>>> Paul

- --
RafaÅ WojdyÅa
Qubes Tools for Windows developer
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