Re: [PATCH] KVM: arm64: Fix ICV_DIR_EL1 trapping detection for pKVM

On Mon, 09 Mar 2026 18:07:45 +0000,
Vincent Donnefort [off-list ref] wrote:

[...]

quoted

quoted

diff --git a/arch/arm64/kvm/hyp/nvhe/hyp-main.c b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
index e7790097db93..0432852228f9 100644
--- a/arch/arm64/kvm/hyp/nvhe/hyp-main.c
+++ b/arch/arm64/kvm/hyp/nvhe/hyp-main.c

@@ -463,6 +463,11 @@ static void handle___vgic_v3_get_gic_config(struct kvm_cpu_context *host_ctxt)
 	cpu_reg(host_ctxt, 1) = __vgic_v3_get_gic_config();
 }
 
+static void handle___vgic_v3_get_ich_vtr_el2(struct kvm_cpu_context *host_ctxt)
+{
+	cpu_reg(host_ctxt, 1) = read_sysreg_s(SYS_ICH_VTR_EL2);
+}
+
 static void handle___vgic_v3_init_lrs(struct kvm_cpu_context *host_ctxt)
 {
 	__vgic_v3_init_lrs();

@@ -622,6 +627,7 @@ static const hcall_t host_hcall[] = {
 	HANDLE_FUNC(__kvm_timer_set_cntvoff),
 	HANDLE_FUNC(__vgic_v3_save_aprs),
 	HANDLE_FUNC(__vgic_v3_restore_vmcr_aprs),
+	HANDLE_FUNC(__vgic_v3_get_ich_vtr_el2),
 	HANDLE_FUNC(__pkvm_reserve_vm),
 	HANDLE_FUNC(__pkvm_unreserve_vm),
 	HANDLE_FUNC(__pkvm_init_vm),

This looks incredibly complicated. Since pKVM forbids late onlining of
CPUs, you are absolutely sure that you have already seen the CPU being
hot-plugged on.

So it would make a lot more sense to just return the current value of
the property you are trying to re-evaluate: you know for sure it
cannot change under your feet.

I have quickly tested the following hack:

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);
+
 	if (is_kernel_in_hyp_mode())
 		res.a1 = read_sysreg_s(SYS_ICH_VTR_EL2);
 	else

which works for me. Could you please give it a go?

That works! I can spin a V2 with that if you want.

I've sent what I had written yesterday. Tested-by appreciated!

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.