On Sun, 4 Jun 2023 12:33:43 +0300
Avihai Horon <avih...@nvidia.com> wrote:
> On 01/06/2023 23:22, Alex Williamson wrote:
> > External email: Use caution opening links or attachments
> >
> >
> > On Tue, 30 May 2023 17:48:20 +0300
> > Avihai Horon <avih...@nvidia.com> wrote:
> >
> >> Add a new VFIO device property x-allow-pre-copy to keep migration
> >> compatibility to/from older QEMU versions that don't have VFIO pre-copy
> >> support.
> > This doesn't make sense to me, vfio migration is not currently
> > supported, it can only be enabled via an experimental flag. AFAIK we
> > have no obligation to maintain migration compatibility against
> > experimental features. Is there any other reason we need a flag to
> > disable pre-copy?
>
> This could give flexibility to do migration between hosts without
> matching VFIO device kernel drivers. E.g., source driver doesn't have
> precopy support and dest driver has or vice versa.
If these are valid scenarios, the protocol should support negotiation
without requiring an experimental flag to do so.
> > OTOH, should this series finally remove the experimental migration
> > flag? Do we require Joao's vIOMMU support to finally make it
> > supportable? Is there something else?
>
> I think that after precopy is accepted we can remove the experimental
> flag, as we'll have the major parts of VFIO migration upstream.
> After that we will still need to add Joao's vIOMMU support and P2P support.
> Do you want me to add a patch to this series that makes VFIO migration
> non-experimental?
I'd keep it as a separate patch with a clearly described dependency on
this series so that we can discuss it separately. Thanks,
Alex
> >> Signed-off-by: Avihai Horon <avih...@nvidia.com>
> >> Reviewed-by: Cédric Le Goater <c...@redhat.com>
> >> ---
> >> include/hw/vfio/vfio-common.h | 1 +
> >> hw/core/machine.c | 1 +
> >> hw/vfio/migration.c | 3 ++-
> >> hw/vfio/pci.c | 2 ++
> >> 4 files changed, 6 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/include/hw/vfio/vfio-common.h b/include/hw/vfio/vfio-common.h
> >> index 1db901c194..a53ecbe2e0 100644
> >> --- a/include/hw/vfio/vfio-common.h
> >> +++ b/include/hw/vfio/vfio-common.h
> >> @@ -146,6 +146,7 @@ typedef struct VFIODevice {
> >> VFIOMigration *migration;
> >> Error *migration_blocker;
> >> OnOffAuto pre_copy_dirty_page_tracking;
> >> + bool allow_pre_copy;
> >> bool dirty_pages_supported;
> >> bool dirty_tracking;
> >> } VFIODevice;
> >> diff --git a/hw/core/machine.c b/hw/core/machine.c
> >> index 1000406211..64ac3fe38e 100644
> >> --- a/hw/core/machine.c
> >> +++ b/hw/core/machine.c
> >> @@ -41,6 +41,7 @@
> >>
> >> GlobalProperty hw_compat_8_0[] = {
> >> { "migration", "multifd-flush-after-each-section", "on"},
> >> + { "vfio-pci", "x-allow-pre-copy", "false" },
> >> };
> >> const size_t hw_compat_8_0_len = G_N_ELEMENTS(hw_compat_8_0);
> >>
> >> diff --git a/hw/vfio/migration.c b/hw/vfio/migration.c
> >> index d8f6a22ae1..cb6923ed3f 100644
> >> --- a/hw/vfio/migration.c
> >> +++ b/hw/vfio/migration.c
> >> @@ -323,7 +323,8 @@ static bool vfio_precopy_supported(VFIODevice
> >> *vbasedev)
> >> {
> >> VFIOMigration *migration = vbasedev->migration;
> >>
> >> - return migration->mig_flags & VFIO_MIGRATION_PRE_COPY;
> >> + return vbasedev->allow_pre_copy &&
> >> + migration->mig_flags & VFIO_MIGRATION_PRE_COPY;
> >> }
> >>
> >> /*
> >> ---------------------------------------------------------------------- */
> >> diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c
> >> index 73874a94de..c69813af7f 100644
> >> --- a/hw/vfio/pci.c
> >> +++ b/hw/vfio/pci.c
> >> @@ -3335,6 +3335,8 @@ static Property vfio_pci_dev_properties[] = {
> >> DEFINE_PROP_ON_OFF_AUTO("x-pre-copy-dirty-page-tracking",
> >> VFIOPCIDevice,
> >> vbasedev.pre_copy_dirty_page_tracking,
> >> ON_OFF_AUTO_ON),
> >> + DEFINE_PROP_BOOL("x-allow-pre-copy", VFIOPCIDevice,
> >> + vbasedev.allow_pre_copy, true),
> >> DEFINE_PROP_ON_OFF_AUTO("display", VFIOPCIDevice,
> >> display, ON_OFF_AUTO_OFF),
> >> DEFINE_PROP_UINT32("xres", VFIOPCIDevice, display_xres, 0),
>
