Re: [PATCH] KVM: arm64: pkvm: Don't reprobe for ICH_VTR_EL2.TDS on CPU hotplug

Hotplugging a CPU off and back on fails with pKVM, as we try to
probe for ICH_VTR_EL2.TDS. In a non-VHE setup, this is achieved
by using an EL2 stub helper. However, the stubs are out of reach
once pKVM has deprivileged the kernel. The CPU never boots.

Since pKVM doesn't allow late onlining of CPUs, we can detect
that protected mode is enforced early on, and return the current
state of the capability.

Fixes: 2a28810cbb8b2 ("KVM: arm64: GICv3: Detect and work around the lack of ICV_DIR_EL1 trapping")
Reported-by: Vincent Donnefort <redacted>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Cc: stable@vger.kernel.org
---
  arch/arm64/kernel/cpufeature.c | 3 +++
  1 file changed, 3 insertions(+)

diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index c31f8e17732a3..947ff71b3b66b 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c

@@ -2345,6 +2345,9 @@ static bool can_trap_icv_dir_el1(const struct arm64_cpu_capabilities *entry,
  	    !is_midr_in_range_list(has_vgic_v3))
  		return false;
  
+	if (system_capabilities_finalized() && is_protected_kvm_enabled())
+		return cpus_have_final_cap(ARM64_HAS_ICH_HCR_EL2_TDIR);