The patch below does not apply to the 4.9-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From da5a3ce66b8bb51b0ea8a89f42aac153903f90fb Mon Sep 17 00:00:00 2001

From: Mark Rutland mark.rutland@arm.com Date: Wed, 17 Oct 2018 17:42:10 +0100 Subject: [PATCH] KVM: arm64: Fix caching of host MDCR_EL2 value

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 christoffer.dall@arm.com Cc: James Morse james.morse@arm.com Cc: Will Deacon will.deacon@arm.com Cc: stable@vger.kernel.org Fixes: 1e947bad0b63b351 ("arm64: KVM: Skip HYP setup when already running in HYP") Tested-by: Robin Murphy robin.murphy@arm.com Signed-off-by: Mark Rutland mark.rutland@arm.com Signed-off-by: Marc Zyngier marc.zyngier@arm.com

diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c index 4ce99bb223bc..4c5ff06b18f9 100644 --- a/virt/kvm/arm/arm.c +++ b/virt/kvm/arm/arm.c @@ -1296,8 +1296,6 @@ static void cpu_init_hyp_mode(void *dummy)

__cpu_init_hyp_mode(pgd_ptr, hyp_stack_ptr, vector_ptr); __cpu_init_stage2(); - - kvm_arm_init_debug(); }

static void cpu_hyp_reset(void) @@ -1315,6 +1313,8 @@ static void cpu_hyp_reinit(void) else cpu_init_hyp_mode(NULL);

+ kvm_arm_init_debug(); + if (vgic_present) kvm_vgic_init_cpu_hardware(); }