Re: [Qemu-devel] [PATCH v3] pc/fwcfg: unbreak migration from qemu-2.5 and qemu-2.6 during firmware boot

[Igor Mammedov]

On Wed, 26 Apr 2017 11:34:04 -0300
Eduardo Habkost <address@hidden> wrote:

> On Tue, Apr 25, 2017 at 05:37:50PM +0200, Igor Mammedov wrote:
> > Since 2.7 commit (b2a575a Add optionrom compatible with fw_cfg DMA version)
> > regressed migration during firmware exection time by
> > abusing fwcfg.dma_enabled property to decide loading
> > dma version of option rom AND by mistake disabling DMA
> > for 2.6 and earlier globally instead of only for option rom.
> > 
> > so 2.6 machine type guest is broken when it already runs
> > firmware in DMA mode but migrated to qemu-2.7(pc-2.6)
> > at that time;
> > 
> > a) qemu-2.6:pc2.6 (fwcfg.dma=on,firmware=dma,oprom=ioport)
> > b) qemu-2.7:pc2.6 (fwcfg.dma=off,firmware=ioport,oprom=ioport)
> > 
> >   to:   a     b
> > from
> > a       OK   FAIL
> > b       OK   OK
> > 
> > So we currently have broken forward migration from
> > qemu-2.6 to qemu-2.[789] that however could be fixed
> > for 2.10 by re-enabling DMA for 2.[56] machine types
> > and allowing dma capable option rom only since 2.7.
> > As result qemu should end up with:
> > 
> > c) qemu-2.10:pc2.6 (fwcfg.dma=on,firmware=dma,oprom=ioport)
> > 
> >    to:  a     b    c
> > from
> > a      OK   FAIL  OK
> > b      OK   OK    OK
> > c      OK   FAIL  OK
> > 
> > where forward migration from qemu-2.6 to qemu-2.10 should
> > work again leaving only qemu-2.[789]:pc-2.6 broken.
> > 
> > Reported-by: Eduardo Habkost <address@hidden>
> > Analyzed-by: Laszlo Ersek <address@hidden>
> > Signed-off-by: Igor Mammedov <address@hidden>
> > Reviewed-by: Laszlo Ersek <address@hidden>  
> 
> Reviewed-by: Eduardo Habkost <address@hidden>

Marcel or Michael,

could you pick up and merge the patch through your tree?