[PATCH v13 37/48] arm64: RMI: Prevent Device mappings for Realms

[Wei-Lin Chang]

On Wed, Mar 18, 2026 at 03:54:01PM +0000, Steven Price wrote:
> Physical device assignment is not supported by RMM v1.0, so it
> doesn't make much sense to allow device mappings within the realm.
> Prevent them when the guest is a realm.
> 
> Signed-off-by: Steven Price <steven.price at arm.com>
> ---
> Changes from v6:
>  * Fix the check in user_mem_abort() to prevent all pages that are not
>    guest_memfd() from being mapped into the protected half of the IPA.
> Changes from v5:
>  * Also prevent accesses in user_mem_abort()
> ---
>  arch/arm64/kvm/mmu.c | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
> 
> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> index ad1300f366df..7d7caab8f573 100644
> --- a/arch/arm64/kvm/mmu.c
> +++ b/arch/arm64/kvm/mmu.c
> @@ -1222,6 +1222,10 @@ int kvm_phys_addr_ioremap(struct kvm *kvm, phys_addr_t guest_ipa,
>  	if (is_protected_kvm_enabled())
>  		return -EPERM;
>  
> +	/* We don't support mapping special pages into a Realm */
> +	if (kvm_is_realm(kvm))
> +		return -EPERM;
> +
>  	size += offset_in_page(guest_ipa);
>  	guest_ipa &= PAGE_MASK;
>  
> @@ -1965,6 +1969,15 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
>  		return 1;
>  	}
>  
> +	/*
> +	 * For now we shouldn't be hitting protected addresses because they are
> +	 * handled in private_memslot_fault(). In the future this check may be

Hi,

What is private_memslot_fault()? I don't see it anywhere in the series &
upstream.

> +	 * relaxed to support e.g. protected devices.
> +	 */
> +	if (vcpu_is_rec(vcpu) &&
> +	    kvm_gpa_from_fault(kvm, fault_ipa) == fault_ipa)
> +		return -EINVAL;
> +

Additionally, there is a hunk almost identical to this one here in added
in patch 27.

Thanks,
Wei-Lin Chang

>  	if (nested)
>  		adjust_nested_fault_perms(nested, &prot, &writable);
>  
> -- 
> 2.43.0
>