Re: [Qemu-devel] [PATCH 1/2] dataplane: drop copy_in_vring_desc()

[Greg Kurz]

On Sun, 28 Jun 2015 15:03:20 +0200
"Michael S. Tsirkin" <address@hidden> wrote:

> On Fri, Jun 26, 2015 at 07:05:07PM +0200, Greg Kurz wrote:
> > On Fri, 26 Jun 2015 18:28:42 +0200
> > "Michael S. Tsirkin" <address@hidden> wrote:
> > 
> > > On Fri, Jun 26, 2015 at 02:18:38PM +0200, Greg Kurz wrote:
> > > > On Fri, 26 Jun 2015 12:28:45 +0200
> > > > Cornelia Huck <address@hidden> wrote:
> > > > 
> > > > > On Fri, 26 Jun 2015 09:32:21 +0200
> > > > > Greg Kurz <address@hidden> wrote:
> > > > > 
> > > > > > During early virtio 1.0 devel, there were several proposals about 
> > > > > > how to
> > > > > > deal with the endianness of the vring descriptor fields:
> > > > > > - convert the decriptor to host endianness in a single place, and 
> > > > > > use its
> > > > > >   fields directly in the code
> > > > > > - keep the descriptor untouched and use virtio memory helpers to 
> > > > > > access its
> > > > > >   fields with the appropriate endianness
> > > > > > 
> > > > > > It seems like both approaches got merged: commit f5a5628cf0b6 
> > > > > > introduces
> > > > > > an extra swap that negates the one brought by commit b0e5d90ebc3e. 
> > > > > > This
> > > > > > breaks boot in SLOF (BE client) when host is ppc64le with the 
> > > > > > following
> > > > > > QEMU error:
> > > > > > 
> > > > > > Failed to map descriptor addr 0x18e2517e00000000 len 268435456
> > > > > > 
> > > > > > A solution could be to revert f5a5628cf0b6, but dropping 
> > > > > > copy_in_vring_desc()
> > > > > > is equivalent and result in a smaller patch.
> > > > > 
> > > > > I'd prefer the revert, as the resulting code is nicer IMHO.
> > > > > 
> > > > 
> > > > Agreed. It is good to clear the endianness noise out of the real code. 
> > > > :)
> > > 
> > > Can you please send v2 that works the way you want it?
> > > 
> > 
> > Taken from a previous mail by Stefan:
> > 
> > "Cornelia already sent "[PATCH] Revert "dataplane: allow virtio-1
> > devices" to revert f5a5628cf0b.  I acked it but the patch is going
> > through Michael Tsirkin."
> > 
> > I guess you just have to take Cornelia's patch + Stefan's ack,
> > and patch 2/2 in my series + Cornelia's rb, and we are all set. :)
> > 
> > FWIW I tested and it works exactly the same.
> 
> Sounds good.
> Can you please test the pci branch from my tree, and confirm?
> 

Sure ! I shall do it tomorrow.

Thanks.

--
Greg

> 
> 
> > > > > But your second patch should apply regardless.
> > > > > 
> > > > 
> > > > Thanks for your feedback.
> > > > 
> > > > > > 
> > > > > > This patch allows SLOF to boot the OS.
> > > > > > 
> > > > > > Signed-off-by: Greg Kurz <address@hidden>
> > > > > > ---
> > > > > >  hw/virtio/dataplane/vring.c |   14 ++------------
> > > > > >  1 file changed, 2 insertions(+), 12 deletions(-)
> > > 
>