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

Steven Price
2026-03-20T16:45:12Z

On 19/03/2026 18:46, Wei-Lin Chang wrote:
> 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@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.

Oh dear, that comment is out of date ;) It's now become gmem_abort()...

>> + * 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.

Which is what this chunk says. It appears I screwed up a rebase at some
point! This whole patch can really be dropped and the
kvm_phys_addr_ioremap() change moved into another patch.

Thanks,
Steve

> Thanks,
> Wei-Lin Chang
>
>> if (nested)
>> adjust_nested_fault_perms(nested, &prot, &writable);
>>
>> --
>> 2.43.0
>>