[PATCH v1] KVM: arm64: Restore POR_EL0 access to host EL0

[Joey Gouly]

CPTR_EL2.E0POE was being cleared in __deactivate_cptr_traps_vhe(), which meant
that any accesses to POR_EL0 from host EL0 would trap and be reported to
userspace as an Illegal instruction. This would happen after running any VM,
regardless if it used POE or not.

Signed-off-by: Joey Gouly <joey.gouly at arm.com>
Link: https://sashiko.dev/#/patchset/20260602155430.2088142-1-maz@kernel.org?part=1
---

Tested by (paraphrased):

	$ ./read_por_el0
	$ ./lkvm run -f kvm-unit-tests/timer.flat
	$ ./read_por_el0 # This gets "Illegal instruction"

Also ran the above flow in a nested VM.

 arch/arm64/kvm/hyp/include/hyp/switch.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/arm64/kvm/hyp/include/hyp/switch.h b/arch/arm64/kvm/hyp/include/hyp/switch.h
index 320cd45d49c5..e9b36a3b27bb 100644
--- a/arch/arm64/kvm/hyp/include/hyp/switch.h
+++ b/arch/arm64/kvm/hyp/include/hyp/switch.h
@@ -181,6 +181,8 @@ static inline void __deactivate_cptr_traps_vhe(struct kvm_vcpu *vcpu)
 		val |= CPACR_EL1_ZEN;
 	if (cpus_have_final_cap(ARM64_SME))
 		val |= CPACR_EL1_SMEN;
+	if (cpus_have_final_cap(ARM64_HAS_S1POE))
+		val |= CPACR_EL1_E0POE;
 
 	write_sysreg(val, cpacr_el1);
 }
-- 
2.25.1