Subject: Re: [PATCH v4 3/3] coco: guest: arm64: Query host IPA-change alignment via RHI

From: Aneesh Kumar K.V <[email-masked]>
Date: Wed, 29 Apr 2026 14:33:55 +0530

Will Deacon <[email-masked]> writes:

> [+Seb for the ITS]
>
> On Mon, Apr 27, 2026 at 12:01:08PM +0530, Aneesh Kumar K.V (Arm) wrote:
>> Add the Realm Host Interface support needed to query host configuration
>> from a Realm guest. Define the RHI hostconf SMCs, add rsi_host_call(), and
>> use them during Realm initialization to retrieve the host IPA-change
>> alignment size.
>> 
>> Expose that alignment through realm_get_hyp_pagesize() and
>> mem_decrypt_granule_size() so shared-buffer allocation and
>> encryption/decryption paths can honor the ipa change page-size requirement.
>> 
>> If the host reports an invalid alignment (when alginment value is not
>> multiple of 4K), do not enable Realm support.
>> 
>> This provides the host alignment information required by the shared buffer
>> alignment changes.
>> 
>> Signed-off-by: Aneesh Kumar K.V (Arm) <[email-masked]>
>> ---
>>  arch/arm64/include/asm/mem_encrypt.h |  3 ++
>>  arch/arm64/include/asm/rhi.h         | 24 +++++++++++++
>>  arch/arm64/include/asm/rsi.h         |  2 ++
>>  arch/arm64/include/asm/rsi_cmds.h    | 10 ++++++
>>  arch/arm64/include/asm/rsi_smc.h     |  7 ++++
>>  arch/arm64/kernel/Makefile           |  2 +-
>>  arch/arm64/kernel/rhi.c              | 54 ++++++++++++++++++++++++++++
>>  arch/arm64/kernel/rsi.c              | 13 +++++++
>>  arch/arm64/mm/mem_encrypt.c          |  8 +++++
>>  9 files changed, 122 insertions(+), 1 deletion(-)
>>  create mode 100644 arch/arm64/include/asm/rhi.h
>>  create mode 100644 arch/arm64/kernel/rhi.c
>
> [...]
>
>> diff --git a/arch/arm64/mm/mem_encrypt.c b/arch/arm64/mm/mem_encrypt.c
>> index 38c62c9e4e74..f5d64bc29c20 100644
>> --- a/arch/arm64/mm/mem_encrypt.c
>> +++ b/arch/arm64/mm/mem_encrypt.c
>> @@ -59,3 +59,11 @@ int set_memory_decrypted(unsigned long addr, int numpages)
>>  	return crypt_ops->decrypt(addr, numpages);
>>  }
>>  EXPORT_SYMBOL_GPL(set_memory_decrypted);
>> +
>> +size_t mem_decrypt_granule_size(void)
>> +{
>> +	if (is_realm_world())
>> +		return max(PAGE_SIZE, realm_get_hyp_pagesize());
>> +	return PAGE_SIZE;
>
> No, this should be indirected via 'struct arm64_mem_crypt_ops' because
> there's nothing particularly unique to realms here. For pKVM protected
> guests using a smaller page-size than the host, we'd presumably need
> something similar for the ITS (where restricted-dma isn't used).
>

Sure, I will rework this to use struct arm64_mem_crypt_ops in the next revision.

-aneesh