tree b9ba5988d2a1ddcd03f49e81783c639be95ac269
parent 74ee55815705c6ada2320309ddf001c348077285
author Alexandru Elisei <alexandru.elisei@arm.com> 1608206457 +0000
committer David Brazdil <dbrazdil@google.com> 1616599619 +0000

arm: pmu: Don't read PMCR if PMU is not present

For arm and arm64, the PMU is an optional part of the architecture.
According to ARM DDI 0487F.b, page D13-3683, accessing PMCR_EL0 when the
PMU is not present generates an undefined exception (one would assume that
this is also true for arm).

The pmu_probe() function reads the register before checking that a PMU is
present, so defer accessing PMCR_EL0 until after we know that it is safe.

This hasn't been a problem so far because there's no hardware in the wild
without a PMU and KVM, contrary to the architecture, has treated the PMU
registers as RAZ/WI if the VCPU doesn't have the PMU feature. However,
that's about to change as KVM will start treating the registers as
undefined when the guest doesn't have a PMU.

Signed-off-by: Alexandru Elisei <alexandru.elisei@arm.com>
Signed-off-by: Andrew Jones <drjones@redhat.com>
Change-Id: I6e3fc4e75fb5239827a68cddaf85f366f3abfcae