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

[Suzuki K Poulose]

On 10/03/2026 08:54, Marc Zyngier wrote:
> 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 <vdonnefort at google.com>
> Signed-off-by: Marc Zyngier <maz at kernel.org>
> Cc: stable at 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);

Is it a worth adding a comment here ? Otherwise this looks very odd -
Returning the system state of a capability for a "hotplugged" CPU.

Otherwise

Reviewed-by: Suzuki K Poulose <suzuki.poulose at arm.com>


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