Re: [PATCH kvmtool 00/13] Implement reset of virtio devices

From: Gerd Hoffmann <kraxel@redhat.com>
To: Julien Thierry <julien.thierry@arm.com>
Cc: will.deacon@arm.com, kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org
Subject: Re: [PATCH kvmtool 00/13] Implement reset of virtio devices
Date: Wed, 5 Dec 2018 11:09:49 +0100	[thread overview]
Message-ID: <20181205100949.bq4zdvn52jltajat@sirius.home.kraxel.org> (raw)
In-Reply-To: <8cc53cd8-1ab3-d7e1-6f21-e40a0447a0fd@arm.com>

On Wed, Dec 05, 2018 at 09:10:33AM +0000, Julien Thierry wrote:
> 
> 
> On 05/12/18 08:21, Gerd Hoffmann wrote:
> > On Tue, Dec 04, 2018 at 11:08:33AM +0000, Julien Thierry wrote:
> >> Hi,
> >>
> >> This series was developped by Jean-Philippe and is needed for a series
> >> I'll be posting shortly after to load firmwares on arm kvmtool.
> >>
> >> Currently, when a guest tries to reset a device, a lot of ressources
> >> aren't reset (threads keep running, virtio queue keep their state, etc).
> >>
> >> When the guest only does the reset to initialize the device and there
> >> were no previous users, there is no noticeable issue. But when a guest
> >> has a firmare + Linux, if the firmware uses a virtio device, Linux will
> >> fail to probe that device.
> >>
> >> This series aim to properly reset the virtio resources when the guests
> >> requests it.
> >>
> >> Reset of net vhost is unsupported for now.
> >>
> >> Patch 1 is a bug fix on ioeventfd
> >> Patch 2-6 provide the core support so devices can implement their reset
> >> Patch 7-13 implements the reset for the various virtio devices
> > 
> > Fails to build:
> > 
> > kraxel@sirius ~/projects/kvmtool (virtio)# make 
> > Makefile:323: Skipping optional libraries: vncserver
> >   CC       virtio/core.o
> > In file included from virtio/core.c:8:0:
> > virtio/core.c: In function ‘virtio_notify_status’:
> > include/kvm/virtio.h:37:3: error: ‘VIRTIO_CONFIG_S_NEEDS_RESET’
> > undeclared (first use in this function)
> >    VIRTIO_CONFIG_S_NEEDS_RESET | \
> >    ^
> > virtio/core.c:232:19: note: in expansion of macro ‘VIRTIO_CONFIG_S_MASK’
> >   vdev->status &= ~VIRTIO_CONFIG_S_MASK;
> > 
> > Yes, it is an older machine (rhel-7), VIRTIO_CONFIG_S_NEEDS_RESET isn't
> > in the system headers (IIRC this bit was added with virtio-1.0).
> > 
> 
> Thanks for reporting the issue. I think this series was initially
> developed with the intent of supporting virtio-1.0 but then reset and
> virtio-1.0 were split into two series.
> 
> I think here I can just remove that bit from the config mask while
> virtio-1.0 is not supported, and things should work.

Fixed that using ...

+#ifndef VIRTIO_CONFIG_S_NEEDS_RESET
+# define VIRTIO_CONFIG_S_NEEDS_RESET 0x40
+#endif

... in include/kvm/virtio.h

With that in place firmware boot works for x86 too.

Well, to be exact, sort of starts working.  There is still the problem
that kvmtool tweaks the linux kernel command line to compensate for
incomplete emulation.  So when booting a kernel from the disk image via
firmware and boot loader you have to apply the same tweaks to the boot
loader config.  At minimum pci=conf1 is required, otherwise the kernel
doesn't find any pci devices ...

cheers,
  Gerd

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