Re: [PATCH v4 07/10] target/arm/cpu: Expose x-mig-hidden-regs and x-mig-safe-missing-regs properties

[Cornelia Huck <cohuck@redhat.com>]

On Mon, Dec 22 2025, Eric Auger <eric.auger@redhat.com> wrote:

> Allows to set both array properties along with arm cpus. Their "x-" prefix
> reminds that those shall be used carefully for distro specific use cases
> to enable cross kernel migration.
>
> This will allow to define such compat machine props like:
>
>     static GlobalProperty arm_virt_kernel_compat_10_1[] = {
>         /* KVM_REG_ARM_VENDOR_HYP_BMAP_2 */
>         { TYPE_ARM_CPU, "x-mig-hidden-regs", "0x6030000000160003" },
>         { TYPE_ARM_CPU, "x-mig-safe-missing-regs",
>           /* TCR_EL1, PIRE0_EL1, PIR_EL1 */
>           "0x603000000013c103, 0x603000000013c512, 0x603000000013c513" },
>     }
>
> The first one means KVM_REG_ARM_VENDOR_HYP_BMAP_2 shall always
> be hidden for machine types older than 10.1. The second one means
> that along with 10.1 machine type we may receive in the incoming
> migration stream, 3 registers that are unknown on destination.
>
> Obviously, using the reg index as defined in
> linux/Documentation/virt/kvm/api.rst is not user friendly. However
> These options are supposed to be used to enable specific, rare cases,
> and in general, by people trying to configure distribution defaults
> familiar with those specific cases.
>
> Signed-off-by: Eric Auger <eric.auger@redhat.com>
>
> ---
>
> v3 -> v4:
> - typo and rewording in the commit description (Connie)
> ---
>  target/arm/cpu.c | 5 +++++
>  1 file changed, 5 insertions(+)

Reviewed-by: Cornelia Huck <cohuck@redhat.com>