Re: [PATCH v8 33/43] arm64: RME: Hide KVM_CAP_READONLY_MEM for realm guests

[Suzuki K Poulose <suzuki.poulose@arm.com>]

On 16/04/2025 14:41, Steven Price wrote:
> For protected memory read only isn't supported by the RMM. While it may
> be possible to support read only for unprotected memory, this isn't
> supported at the present time.
> 
> Note that this does mean that ROM (or flash) data cannot be emulated
> correctly by the VMM as the stage 2 mappings are either always
> read/write or are trapped as MMIO (so don't support operations where the
> syndrome information doesn't allow emulation, e.g. load/store pair).
> 
> This restriction can be lifted in the future by allowing the stage 2

minor nit: s/allowing the/allowing the unprotected/

> mappings to be made read only.
> 
> Signed-off-by: Steven Price <steven.price@arm.com>

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

> ---
> Changes since v7:
>   * Updated commit message to spell out the impact on ROM/flash
>     emulation.
> ---
>   arch/arm64/kvm/arm.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
> index 8060e25afbd0..4780e3af1bb9 100644
> --- a/arch/arm64/kvm/arm.c
> +++ b/arch/arm64/kvm/arm.c
> @@ -340,7 +340,6 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
>   	case KVM_CAP_ONE_REG:
>   	case KVM_CAP_ARM_PSCI:
>   	case KVM_CAP_ARM_PSCI_0_2:
> -	case KVM_CAP_READONLY_MEM:
>   	case KVM_CAP_MP_STATE:
>   	case KVM_CAP_IMMEDIATE_EXIT:
>   	case KVM_CAP_VCPU_EVENTS:
> @@ -355,6 +354,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
>   		r = 1;
>   		break;
>   	case KVM_CAP_COUNTER_OFFSET:
> +	case KVM_CAP_READONLY_MEM:
>   	case KVM_CAP_SET_GUEST_DEBUG:
>   		r = !kvm_is_realm(kvm);
>   		break;