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Re: [Qemu-ppc] [PATCH v3] virtio-pci: fix migration for pci bus master
From: |
Michael S. Tsirkin |
Subject: |
Re: [Qemu-ppc] [PATCH v3] virtio-pci: fix migration for pci bus master |
Date: |
Tue, 21 Oct 2014 15:10:22 +0300 |
On Tue, Oct 21, 2014 at 01:35:39PM +0200, Alexander Graf wrote:
>
>
> On 21.10.14 12:16, Michael S. Tsirkin wrote:
> > On Mon, Oct 20, 2014 at 06:08:56PM +0200, Alexander Graf wrote:
> >>
> >>
> >> On 20.10.14 08:58, Michael S. Tsirkin wrote:
> >>> Current support for bus master (clearing OK bit) together with the need to
> >>> support guests which do not enable PCI bus mastering, leads to extra
> >>> state in
> >>> VIRTIO_PCI_FLAG_BUS_MASTER_BUG bit, which isn't robust in case of
> >>> cross-version
> >>> migration for the case when guests use the device before setting
> >>> DRIVER_OK.
> >>>
> >>> Rip out this code, and replace it:
> >>> - Modern QEMU doesn't need VIRTIO_PCI_FLAG_BUS_MASTER_BUG
> >>> so just drop it for latest machine type.
> >>> - For compat machine types, set PCI_COMMAND if DRIVER_OK
> >>> is set.
> >>>
> >>> As this is needed for 2.1 for both pc and ppc, move PC_COMPAT macros from
> >>> pc.h
> >>> to a new common header.
> >>>
> >>> Reviewed-by: Greg Kurz <address@hidden>
> >>> Tested-by: Greg Kurz <address@hidden>
> >>> Signed-off-by: Michael S. Tsirkin <address@hidden>
> >>> ---
> >>>
> >>> Alexander, could you pls ack me merging this?
> >>> Thanks!
> >>
> >> Have you tried whether this works with old kernel versions? We
> >> introduced the broken flag for very specific old kernel versions that
> >> got their flags wrong IIRC.
> >>
> >>
> >> Alex
> >
> > Yes. The point is that since 2.1 the broken flag isn't effective
> > anymore: when bus master is off, PCI blocks outgoing transactions and
> > setting internal flags isn't going to help.
> >
> > Instead, we detect a buggy guest and immediately enable bus master for
> > it - no need for a separate flag.
>
> Ok, works for me then.
>
>
> Alex
cool.
Gerd tells me there's a conflict with your next tree:
would you like for me to wait until it's merged,
or go ahead and send pull request and rebase yours on top?
--
MST