Commit da5a3ce6 authored Oct 17, 2018 by Mark Rutland Committed by Marc Zyngier Oct 17, 2018

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: 1e947bad ("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>

parent fd2ef358

virt/kvm/arm/arm.c

+2 −2

Original line number	Diff line number	Diff line
		@@ -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();
		}

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