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

[Steven Price]

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Oh dear, that comment is out of date ;) It's now become gmem_abort()...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