On Wed, 4 Mar 2026, Eric Auger wrote:
> Before linux v6.13 those registers were erroneously unconditionally
> exposed and this was fixed by commits:
> - 0fcb4eea5345 ("KVM: arm64: Hide TCR2_EL1 from userspace when
> disabled for guests")
> - a68cddbe47ef ("KVM: arm64: Hide S1PIE registers from userspace
> when disabled for guests")
> in v6.13.
>
> This means if we migrate from an old kernel host to a >= 6.13 kernel
> host, migration currently fails.
>
> Declare cpreg migration tolerance for those registers.
>
> Signed-off-by: Eric Auger <eric.auger@redhat.com>
Reviewed-by: Sebastian Ott <sebott@redhat.com>
> ---
> target/arm/cpu64.c | 26 ++++++++++++++++++++++++++
> 1 file changed, 26 insertions(+)
>
> diff --git a/target/arm/cpu64.c b/target/arm/cpu64.c
> index d6feba220e8..4cfddc6e8c0 100644
> --- a/target/arm/cpu64.c
> +++ b/target/arm/cpu64.c
> @@ -810,6 +810,31 @@ static void aarch64_a53_initfn(Object *obj)
> define_cortex_a72_a57_a53_cp_reginfo(cpu);
> }
>
> +static void kvm_arm_set_cpreg_mig_tolerances(ARMCPU *cpu)
> +{
> + /*
> + * Registers that may be in the incoming stream and not exposed
> + * on the destination
> + */
> +
> + /*
> + * TCR_EL1 was erroneously unconditionnally exposed before linux v6.13.
> + * See commit 0fcb4eea5345 ("KVM: arm64: Hide TCR2_EL1 from userspace
> + * when disabled for guests")
> + */
> + arm_register_cpreg_mig_tolerance(cpu, ARM64_SYS_REG(3, 0, 2, 0, 3),
> + 0, 0, ToleranceNotOnBothEnds);
> + /*
> + * PIRE0_EL1 and PIR_EL1 were erroneously unconditionnally exposed
> + * before linux v6.13. See commit a68cddbe47ef ("KVM: arm64: Hide
> + * S1PIE registers from userspace when disabled for guests")
> + */
> + arm_register_cpreg_mig_tolerance(cpu, ARM64_SYS_REG(3, 0, 10, 2, 2),
> + 0, 0, ToleranceNotOnBothEnds);
> + arm_register_cpreg_mig_tolerance(cpu, ARM64_SYS_REG(3, 0, 10, 2, 3),
> + 0, 0, ToleranceNotOnBothEnds);
> +}
> +
> static void aarch64_host_initfn(Object *obj)
> {
> ARMCPU *cpu = ARM_CPU(obj);
> @@ -822,6 +847,7 @@ static void aarch64_host_initfn(Object *obj)
> #endif
>
> #if defined(CONFIG_KVM)
> + kvm_arm_set_cpreg_mig_tolerances(cpu);
> kvm_arm_set_cpu_features_from_host(cpu);
> aarch64_add_sve_properties(obj);
> #elif defined(CONFIG_HVF)
> --
> 2.53.0
>
>