[PATCH] irqchip: GICv3: ITS: don't assume 64K page size in its_alloc_tables

[Stuart Yoder]

> -----Original Message-----
> From: Marc Zyngier [mailto:marc.zyngier at arm.com]
> Sent: Monday, May 18, 2015 9:09 AM
> To: Yoder Stuart-B08248; tglx at linutronix.de
> Cc: linux-arm-kernel at lists.infradead.org
> Subject: Re: [PATCH] irqchip: GICv3: ITS: don't assume 64K page size in its_alloc_tables
> 
> On 18/05/15 14:38, Stuart Yoder wrote:
> >
> >
> >> -----Original Message-----
> >> From: Marc Zyngier [mailto:marc.zyngier at arm.com]
> >> Sent: Monday, May 18, 2015 8:23 AM
> >> To: Yoder Stuart-B08248; tglx at linutronix.de
> >> Cc: linux-arm-kernel at lists.infradead.org
> >> Subject: Re: [PATCH] irqchip: GICv3: ITS: don't assume 64K page size in its_alloc_tables
> >>
> >> Hi Stuart,
> >>
> >> On 15/05/15 00:02, Stuart Yoder wrote:
> >>> its_alloc_tables() needs to account for page sizes other than
> >>> 64KB.  Without this change, when PAGE_SIZE=4KB its_alloc_tables()
> >>> gets stuck in an infinite loop.
> >>>
> >>> Signed-off-by: Stuart Yoder <stuart.yoder at freescale.com>
> >>> ---
> >>>
> >>> think this should go into 4.1 if at all possible...without it I am
> >>> unable to boot a 4.1 kernel on the LS2085 SoC
> >>
> >> What you are suggesting here is a effectively a revert of commit
> >> 790b57a, which would break other implementations.
> >>
> >> Can you please explain the actual issue? I'm failing to see how you end
> >> up in an infinite loop here (the system page size and the ITS base
> >> granule should be completely unrelated...).
> >
> > Here is the problem line:
> >
> >       val |= (alloc_size / psz) - 1;
> >
> > In our case:
> >    alloc_size=16K
> >    psz=64K
> >
> > ...so (alloc_size / psz) = 0, and thus val becomes -1, and everything
> > is screwed up.  We get stuck in a loop to retry_baser:
> 
> If alloc_size is 16k, you have an order of 2, and I have to assume this
> is an allocation for a device table (otherwise order would be 4). So
> things fail because we've computed an alloc_size smaller than what we
> want to allocate as a minimum.
> 
> Isn't that exactly what Minghuan's patch fixes?

Yes.  I'll get with Minghuan and between the 2 of us we'll get a properly
commented version of his patch sent out.

Thanks,
Stuart