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

[Greg KH <gregkh@linuxfoundation.org>]

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?

thanks,

greg k-h