On Mon, 2 Oct 2023 21:41:55 +0200 Laszlo Ersek <ler...@redhat.com> wrote:
> On 10/2/23 21:26, Alex Williamson wrote: > > On Mon, 2 Oct 2023 20:24:11 +0200 > > Laszlo Ersek <ler...@redhat.com> wrote: > > > >> On 10/2/23 16:41, Alex Williamson wrote: > >>> On Mon, 2 Oct 2023 15:38:10 +0200 > >>> Cédric Le Goater <c...@redhat.com> wrote: > >>> > >>>> On 10/2/23 13:11, marcandre.lur...@redhat.com wrote: > >>>>> From: Marc-André Lureau <marcandre.lur...@redhat.com> > >>>>> > >>>>> RAMFB migration was unsupported until now, let's make it conditional. > >>>>> The following patch will prevent machines <= 8.1 to migrate it. > >>>>> > >>>>> Signed-off-by: Marc-André Lureau <marcandre.lur...@redhat.com> > >>>> Maybe localize the new 'ramfb_migrate' attribute close to 'enable_ramfb' > >>>> in VFIOPCIDevice. Anyhow, > >>> > >>> Shouldn't this actually be tied to whether the device is migratable > >>> (which for GVT-g - the only ramfb user afaik - it's not)? What does it > >>> mean to have a ramfb-migrate=true property on a device that doesn't > >>> support migration, or false on a device that does support migration. I > >>> don't understand why this is a user controllable property. Thanks, > >> > >> The comments in <https://bugzilla.redhat.com/show_bug.cgi?id=1859424> > >> (which are unfortunately not public :/ ) suggest that ramfb migration > >> was simply forgotten when vGPU migration was implemented. So, "now > >> that vGPU migration is done", this should be added. > >> > >> Comment 8 suggests that the following domain XML snippet > >> > >> <hostdev mode='subsystem' type='mdev' managed='no' > >> model='vfio-pci' display='on' ramfb='on'> <source> > >> <address uuid='b155147a-663a-4009-ae7f-e9a96805b3ce'/> > >> </source> > >> <alias name='ua-b155147a-663a-4009-ae7f-e9a96805b3ce'/> > >> <address type='pci' domain='0x0000' bus='0x07' slot='0x00' > >> function='0x0'/> </hostdev> > >> > >> is migratable, but the ramfb device malfunctions on the destination > >> host. > >> > >> There's also a huge QEMU cmdline in comment#0 of the bug; I've not > >> tried to read that. > >> > >> AIUI BTW the property is not for the user to control, it's just a > >> compat knob for versioned machine types. AIUI those are usually > >> implemented with such (user-visible / -tweakable) device properties. > > > > If it's not for user control it's unfortunate that we expose it to the > > user at all, but should it at least use the "x-" prefix to indicate that > > it's not intended to be an API? > > I *think* it was your commit db32d0f43839 ("vfio/pci: Add option to > disable GeForce quirks", 2018-02-06) that hda introduced me to the "x-" > prefixed properties! > > For some reason though, machine type compat knobs are never named like > that, AFAIR. Maybe I'm misunderstanding your comment, but it appears quite common to use "x-" prefix things in the compat tables... GlobalProperty hw_compat_8_0[] = { { "migration", "multifd-flush-after-each-section", "on"}, { TYPE_PCI_DEVICE, "x-pcie-ari-nextfn-1", "on" }, { TYPE_VIRTIO_NET, "host_uso", "off"}, { TYPE_VIRTIO_NET, "guest_uso4", "off"}, { TYPE_VIRTIO_NET, "guest_uso6", "off"}, }; const size_t hw_compat_8_0_len = G_N_ELEMENTS(hw_compat_8_0); GlobalProperty hw_compat_7_2[] = { { "e1000e", "migrate-timadj", "off" }, { "virtio-mem", "x-early-migration", "false" }, { "migration", "x-preempt-pre-7-2", "true" }, { TYPE_PCI_DEVICE, "x-pcie-err-unc-mask", "off" }, }; const size_t hw_compat_7_2_len = G_N_ELEMENTS(hw_compat_7_2); [etc] > > It's still odd to think that we can > > have scenarios of a non-migratable vfio device registering a migratable > > ramfb, and vice versa, but I suppose in the end it doesn't matter. > > I do think it matters! For one, if migration is not possible with > vfio-pci-nohotplug, then how can QE (or anyone else) *test* the patch > (i.e. that it makes a difference)? In that case, the ramfb_setup() call > from vfio-pci-nohotplug should just open-code "false" for the > "migratable" parameter. Some vfio devices support migration, most don't. I was thinking ramfb_setup might be called with something like: (vdev->ramfb_migrate && vdev->enable_migration) so that at least the ramfb migration state matches the device, but I think ultimately it only saves a little bit of overhead in registering the vmstate, either one not supporting migration should block migration. Hmm, since enable_migration is auto/on/off, it seems like device realize should fail if set to 'on' and ramfb_migrate is false. I think that's the only way the device options don't become self contradictory. Thanks, Alex
