BugLink: https://bugs.launchpad.net/bugs/1818803

commit 8208d170 upstream.

The way we allocate events works fine in most cases, except
when multiple PCI devices share an ITS-visible DevID, and that
one of them is trying to use MultiMSI allocation.

In that case, our allocation is not guaranteed to be zero-based
anymore, and we have to make sure we allocate it on a boundary
that is compatible with the PCI Multi-MSI constraints.

Fix this by allocating the full region upfront instead of iterating
over the number of MSIs. MSI-X are always allocated one by one,
so this shouldn't change anything on that front.

Fixes: b48ac83d ("irqchip: GICv3: ITS: MSI support")
Cc: stable@vger.kernel.org
Reported-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Tested-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
[ardb: rebased onto v4.9.153, should apply cleanly onto v4.4.y as well]
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Juerg Haefliger <juergh@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>