commit da5a3ce66b8bb51b0ea8a89f42aac153903f90fb upstream.
At boot time, KVM stashes the host MDCR_EL2 value, but only does this
when the kernel is not running in hyp mode (i.e. is non-VHE). In these
cases, the stashed value of MDCR_EL2.HPMN happens to be zero, which can
lead to CONSTRAINED UNPREDICTABLE behaviour.
Since we use this value to derive the MDCR_EL2 value when switching
to/from a guest, after a guest have been run, the performance counters
do not behave as expected. This has been observed to result in accesses
via PMXEVTYPER_EL0 and PMXEVCNTR_EL0 not affecting the relevant
counters, resulting in events not being counted. In these cases, only
the fixed-purpose cycle counter appears to work as expected.
Fix this by always stashing the host MDCR_EL2 value, regardless of VHE.
Cc: Christopher Dall <firstname.lastname@example.org>
Cc: James Morse <email@example.com>
Cc: Will Deacon <firstname.lastname@example.org>
Fixes: 1e947bad ("arm64: KVM: Skip HYP setup when already running in HYP")
Tested-by: Robin Murphy <email@example.com>
Signed-off-by: Mark Rutland <firstname.lastname@example.org>
Signed-off-by: Marc Zyngier <email@example.com>
Signed-off-by: Greg Kroah-Hartman <firstname.lastname@example.org>