Re: [PATCH] Paravirt framebuffer frontend kernel support [1/5]

[Steven Smith <sos22-xen@srcf.ucam.org>]

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> > There are still a couple of things from the last round which are
> > unfixed.  This is mostly my fault for going on holiday at an
> > inconvenient time; sorry about that.
> We won't begrudge you a holiday -- hope it was a good one :-)
Yes, thank you.

> > The big problem with this is that you don't support shadow translate
> > mode guests, because the frontend exposes mfns directly to the
> > backend.  The correct way of fixing this is to use grant tables, but,
> > as Anthony pointed out, that's quite hard due to the amount of memory
> > you need to grant access to.
> > 
> > The easy way of doing this would be to just increase the size of the
> > grant tables.  Alternatively, you could add support for granting
> > access to ranges of memory, but that sounds like a whole lot of work.
> > 
> > You could also put in a quick hack of just translating the mfns in the
> > backend if the frontend is in shadow translate mode, but that's not
> > really very nice.
> I wouldn't complain if we go the route Keir suggested and have Xen do
> it ;-)  But if not, I think that given the size of the memory in
> question + grant tables, the quick hack is probably going to be the
> "right" thing for this case.
Okay.  Adding translations to the hypervisor isn't going to happen
until after 3.0.3, so we should probably just leave this for a little
while.

> > > diff -r 5fa9b746d24f -r 510c6bceb87f linux-2.6-xen-sparse/arch/i386/kernel/setup-xen.c
> > > --- a/linux-2.6-xen-sparse/arch/i386/kernel/setup-xen.c	Sat Sep 02 12:11:54 2006 +0100
> > > +++ b/linux-2.6-xen-sparse/arch/i386/kernel/setup-xen.c	Sat Sep 02 15:11:17 2006 -0400
> > > @@ -1866,8 +1866,12 @@ void __init setup_arch(char **cmdline_p)
> > >  #endif
> > >  #endif
> > >  	} else {
> > > +#if defined(CONFIG_VT) && defined(CONFIG_DUMMY_CONSOLE)
> > > +		conswitchp = &dummy_con;
> > > +#else
> > >  		extern int console_use_vt;
> > >  		console_use_vt = 0;
> > > +#endif
> > >  	}
> > >  }
> > Not quite sure I understand what this is trying to achieve, or why it's
> > related to the PV framebuffer stuff.
> It makes it so that console switching is achieved by the dummy console
> and then when the fbcon driver is loaded, it takes over.  
Okay.

> 
> [snip]
> > Perhaps XEN_KEYBOARD should depend on XEN_FRAMEBUFFER, given that it
> > doesn't work without it.
> Yeah, seems reasonable enough -- I've added to my tree.
Thanks.

> > >  config XEN_SCRUB_PAGES
> > >  	bool "Scrub memory before freeing it to Xen"
> > >  	default y
> > > diff -r 5fa9b746d24f -r 510c6bceb87f linux-2.6-xen-sparse/drivers/xen/Makefile
> > > --- a/linux-2.6-xen-sparse/drivers/xen/Makefile	Sat Sep 02 12:11:54 2006 +0100
> > > +++ b/linux-2.6-xen-sparse/drivers/xen/Makefile	Sat Sep 02 15:11:17 2006 -0400
> > > @@ -15,3 +15,5 @@ obj-$(CONFIG_XEN_NETDEV_FRONTEND)	+= net
> > >  obj-$(CONFIG_XEN_NETDEV_FRONTEND)	+= netfront/
> > >  obj-$(CONFIG_XEN_PCIDEV_BACKEND)	+= pciback/
> > >  obj-$(CONFIG_XEN_PCIDEV_FRONTEND)	+= pcifront/
> > > +obj-$(CONFIG_XEN_FRAMEBUFFER)		+= xenfb/
> > > +obj-$(CONFIG_XEN_KEYBOARD)		+= xenkbd/
> > > diff -r 5fa9b746d24f -r 510c6bceb87f linux-2.6-xen-sparse/mm/memory.c
> > > --- a/linux-2.6-xen-sparse/mm/memory.c	Sat Sep 02 12:11:54 2006 +0100
> > > +++ b/linux-2.6-xen-sparse/mm/memory.c	Sat Sep 02 15:11:17 2006 -0400
> > > @@ -881,6 +881,7 @@ unsigned long zap_page_range(struct vm_a
> > >  		tlb_finish_mmu(tlb, address, end);
> > >  	return end;
> > >  }
> > > +EXPORT_SYMBOL(zap_page_range);
> > It's unfortunate that we have to modify an upstream file here, but I
> > can't really see any alternative.
> Well, if we don't allow the framebuffer to be modular then it doesn't
> have to be exported.  But that also seems like the wrong answer :-)
Yeah, adding the EXPORT_SYMBOL is the right thing to do here, it's
just kind of annoying.  Oh well.

> 
> > > +#if 0
> > > +        /* if we're not set up to use graphics mode, then don't initialize */
> > > +	if (xenbus_scanf(XBT_NIL, "console", "use_graphics", "%d", &ret) < 0)
> > > +		return -ENODEV;
> > > +	if (ret == 0)
> > > +		return -ENODEV;
> > > +#endif
> > That's interesting.  What is this here for?
> It looks like it got accidentally #if 0'd while merging patches.
> Whoops.  Basically, if the guest isn't set up to use a graphical
> console, then we shouldn't initialize the devices.
That seems like a good idea.  Please put this back in.

Steven.

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