Re: Is: SKB_MAX_LEN bites again. Was: Re: bug disabling guest interface

Jacek Milewicz
Fri, 08 Mar 2013 22:09:56 -0000

> > > Is there any further information on a possible fix for this?
Thoughts?
> > > Ideas? As it seems to be hitting multiple sites, I''d
like to get it
> > fixed asap...
> >
> > There are 3 ways I can see this fixed:
> > - update guests so all have same MAX_SKB_FRAGS (that includes windows
> > drivers (windows drivers use 19 for MAX_SKB_FRAGS)) -add some sort of
> > negotiation between host and guest
> > - change MAX_SKB_FRAGS to 19 to accommodate all guests
> >
> > Unfortunately first one requires changes to the guest and most
don''t
> > have that luxury. So the only way I see it could be fixed without
> > breaking compatibility even more  is
>
> Ugh. The negotiations between host and guest is probably the best
choice.
> The issues you are going to hit are that you might need to redo the skbs
to
> match what the frontend''s max is.
>
> Annie, Wei, Ian - were there some RFC patches floating around for this?
>

As much as I agree that negotiation is the best option in long term. It
relies on people upgrading their kernels - and this is not the case (only
people running kernels from before 2011-12-23 are affected by this bug
(I''m not sure about other platforms)).
And in a lot of cases (VPS providers) there is no easy way to upgrade
guest kernels.