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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: 1e947bad0b ("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>
hifive-unleashed-5.1
Mark Rutland 2018-10-17 17:42:10 +01:00 committed by Marc Zyngier
parent fd2ef35828
commit da5a3ce66b
1 changed files with 2 additions and 2 deletions
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4
virt/kvm/arm/arm.c
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@ -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();
}