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Subject[PATCH 4.9 82/83] KVM: arm64: Fix caching of host MDCR_EL2 value
4.9-stable review patch.  If anyone has any objections, please let me know.


From: Mark Rutland <>

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

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 <>
Cc: James Morse <>
Cc: Will Deacon <>
Fixes: 1e947bad0b63b351 ("arm64: KVM: Skip HYP setup when already running in HYP")
Tested-by: Robin Murphy <>
Signed-off-by: Mark Rutland <>
Signed-off-by: Marc Zyngier <>
Signed-off-by: Greg Kroah-Hartman <>

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);
- 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)
+ kvm_arm_init_debug();

static void cpu_hyp_reset(void)

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