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

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----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
> 
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
> 
> 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.

> 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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