Re: [PATCH] irqchip/gic-v3-its: Ensure nr_ites >= nr_lpis

Greg KH
2018-03-19T07:37:29Z

On Mon, Mar 19, 2018 at 08:37:07AM +0100, Greg KH wrote:
> On Mon, Mar 19, 2018 at 03:28:40PM +0800, Ard Biesheuvel wrote:
> > On 19 March 2018 at 15:27, Ard Biesheuvel <ard.biesheuvel@linaro.org> wrote:
> > > Commit 4f2c7583e33e upstream.
> > >
> > > When struct its_device instances are created, the nr_ites member
> > > will be set to a power of 2 that equals or exceeds the requested
> > > number of MSIs passed to the msi_prepare() callback. At the same
> > > time, the LPI map is allocated to be some multiple of 32 in size,
> > > where the allocated size may be less than the requested size
> > > depending on whether a contiguous range of sufficient size is
> > > available in the global LPI bitmap.
> > >
> > > This may result in the situation where the nr_ites < nr_lpis, and
> > > since nr_ites is what we program into the hardware when we map the
> > > device, the additional LPIs will be non-functional.
> > >
> > > For bog standard hardware, this does not really matter. However,
> > > in cases where ITS device IDs are shared between different PCIe
> > > devices, we may end up allocating these additional LPIs without
> > > taking into account that they don't actually work.
> > >
> > > So let's make nr_ites at least 32. This ensures that all allocated
> > > LPIs are 'live', and that its_alloc_device_irq() will fail when
> > > attempts are made to allocate MSIs beyond what was allocated in
> > > the first place.
> > >
> > > Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> > > [maz: updated comment]
> > > Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
> > > [ardb: trivial tweak of unrelated context]
> > > Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> > > ---
> >
> > Please apply to v4.9
>
> What about 4.14.y and 4.15.y? Why only add it to one really old tree,
> you don't want people updating to a newer kernel and have a regression,
> right?

Ah, now I see your other email, sorry, nevermind...