Re: [PATCH v2] arm64: rsi: Correct type of realm_config::hash_algo

[Suzuki K Poulose <suzuki.poulose@arm.com>]

On 14/10/2026 10:53, Catalin Marinas wrote:
> Thanks for respinning.
> 
> On Wed, Oct 14, 2026 at 11:43:23AM +0900, Kohei Enju wrote:
>> The RMM specification defines RsiHashAlgorithm as an 8-bit type, but
>> realm_config::hash_algo is currently declared as unsigned long.
>>
>> There are currently no upstream users of this field, so the mismatch
>> does not cause an observable issue today. However, a proposed series
>> adding support for Realm measurement registers uses this field and
>> exposes a bug caused by the incorrect type.
> 
> It should be clear the bug is in the RMM implementation. The patch here
> is more like defensive programming when the RMM doesn't honour the
> interface and zero the unused bits. I can fix the text when applying.
> 
>> Change hash_algo to u8 to match the RMM specification while preserving
>> the size and layout of struct realm_config.
>>
>> Link: https://lore.kernel.org/all/20260413084957.327661-4-sami.mujawar@arm.com/
>> Signed-off-by: Kohei Enju <enju.kohei@fujitsu.com>
>> ---
>> Changes in v2:
>> - Drop the inner union and padding around hash_algo (Catalin)
>> - Link to v1: https://patch.msgid.link/20260929-cca-b4-rsi-fix-hash_algo-type-rebase-v1-1-6932cf0aa605@fujitsu.com
> 
> In theory we could add a fixes tag for reference but not worth cc
> stable.
> 
> Fixes: b880a80011f5 ("arm64: rsi: Add RSI definitions")
> 
>> ---
>>   include/linux/arm-smccc-rsi.h | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/include/linux/arm-smccc-rsi.h b/include/linux/arm-smccc-rsi.h
>> index fddb77986f70..cca881ddfdba 100644
>> --- a/include/linux/arm-smccc-rsi.h
>> +++ b/include/linux/arm-smccc-rsi.h
>> @@ -128,7 +128,7 @@ struct realm_config {
>>   	union {
>>   		struct {
>>   			unsigned long ipa_bits; /* Width of IPA in bits */
>> -			unsigned long hash_algo; /* Hash algorithm */
>> +			u8 hash_algo; /* Hash algorithm */
>>   		};
>>   		u8 pad[0x200];
>>   	};
> 
> Suzuki, are you ok with this patch?

Yep, looks good to me.

> 
> As a separate patch, we need to add some static_assert() for the offsets
> and the size of the realm_config structure. We do this in
> arm-smccc-rmi.h already.

I was going to suggest that and possibly rename the "pad" to sizers. For
now this is fine, but would be good to do that when we add the newer
  fields for RSI v2.0


> 
> There's a similar realm_params structure in arm-smccc-rmi.h but,
> IIUC, the hash_algo there is written by the kernel, so unsigned long is
> fine.

Correct. It is an input to the RMM.

Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>

Cheers
Suzuki>