On Mon, 2 Oct 2023 21:41:55 +0200
Laszlo Ersek <lersek@redhat.com> wrote:
On 10/2/23 21:26, Alex Williamson wrote:
On Mon, 2 Oct 2023 20:24:11 +0200
Laszlo Ersek <lersek@redhat.com> wrote:
On 10/2/23 16:41, Alex Williamson wrote:
On Mon, 2 Oct 2023 15:38:10 +0200
Cédric Le Goater <clg@redhat.com> wrote:
On 10/2/23 13:11, marcandre.lureau@redhat.com wrote:
From: Marc-André Lureau <marcandre.lureau@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.lureau@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.