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

Aneesh Kumar K.V
2026-04-29T09:04:02Z

Will Deacon <will@kernel.org> 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) <aneesh.kumar@kernel.org>
>> ---
>> 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