This is a note to let you know that I've just added the patch titled KVM: arm64: Fix caching of host MDCR_EL2 value to the 4.9-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: kvm-arm64-fix-caching-of-host-mdcr_el2-value.patch and it can be found in the queue-4.9 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From da5a3ce66b8bb51b0ea8a89f42aac153903f90fb Mon Sep 17 00:00:00 2001 From: Mark Rutland <mark.rutland@xxxxxxx> Date: Wed, 17 Oct 2018 17:42:10 +0100 Subject: KVM: arm64: Fix caching of host MDCR_EL2 value From: Mark Rutland <mark.rutland@xxxxxxx> 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 <christoffer.dall@xxxxxxx> Cc: James Morse <james.morse@xxxxxxx> Cc: Will Deacon <will.deacon@xxxxxxx> Cc: stable@xxxxxxxxxxxxxxx Fixes: 1e947bad0b63b351 ("arm64: KVM: Skip HYP setup when already running in HYP") Tested-by: Robin Murphy <robin.murphy@xxxxxxx> Signed-off-by: Mark Rutland <mark.rutland@xxxxxxx> Signed-off-by: Marc Zyngier <marc.zyngier@xxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- arch/arm/kvm/arm.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) --- a/arch/arm/kvm/arm.c +++ b/arch/arm/kvm/arm.c @@ -1092,8 +1092,6 @@ static void cpu_init_hyp_mode(void *dumm __cpu_init_hyp_mode(pgd_ptr, hyp_stack_ptr, vector_ptr); __cpu_init_stage2(); - - kvm_arm_init_debug(); } static void cpu_hyp_reinit(void) @@ -1108,6 +1106,8 @@ static void cpu_hyp_reinit(void) if (__hyp_get_vectors() == hyp_default_vectors) cpu_init_hyp_mode(NULL); } + + kvm_arm_init_debug(); } static void cpu_hyp_reset(void) Patches currently in stable-queue which might be from mark.rutland@xxxxxxx are queue-4.9/kvm-arm64-fix-caching-of-host-mdcr_el2-value.patch