Re: [PATCH v13 12/18] target/s390x: Support protected key AES ECB for cpacf km instruction

[Harald Freudenberger <freude@linux.ibm.com>]

On 2026-08-05 00:48, Ilya Leoshkevich wrote:
> On 8/3/26 18:12, Harald Freudenberger wrote:
>> Support the subfunctions CPACF_KM_PAES_128, CPACF_KM_PAES_192
>> and CPACF_KM_PAES_256 for the cpacf km instruction.
>> 
>> Tested-by: Holger Dengler <dengler@linux.ibm.com>
>> Reviewed-by: Finn Callies <fcallies@linux.ibm.com>
>> Signed-off-by: Harald Freudenberger <freude@linux.ibm.com>
>> ---
>>   target/s390x/gen-features.c      |  3 ++
>>   target/s390x/tcg/cpacf.h         |  4 ++
>>   target/s390x/tcg/cpacf_aes.c     | 91 
>> ++++++++++++++++++++++++++++++++
>>   target/s390x/tcg/crypto_helper.c |  7 +++
>>   4 files changed, 105 insertions(+)
> 
> [...]
> 
>> +
>> +    /* process up to MAX_BLOCKS_PER_RUN aes blocks */
>> +    for (i = 0; i < MAX_BLOCKS_PER_RUN && len >= AES_BLOCK_SIZE; i++) 
>> {
>> +        aes_read_block(env, mmu_idx, ra, *src_ptr_reg + done, in);
>> +        if (mod) {
>> +            AES_decrypt(in, out, &exkey);
>> +        } else {
>> +            AES_encrypt(in, out, &exkey);
>> +        }
>> +        aes_write_block(env, mmu_idx, ra, *dst_ptr_reg + done, out);
>> +        len -= AES_BLOCK_SIZE;
>> +        done += AES_BLOCK_SIZE;
>> +    }
>> +
>> +    *src_ptr_reg = deposit64(*src_ptr_reg, 0, addr_reg_size,
>> +                             *src_ptr_reg + done);
>> +    *dst_ptr_reg = deposit64(*dst_ptr_reg, 0, addr_reg_size,
>> +                             *dst_ptr_reg + done);
>> +    *src_len_reg -= done;
> 
> Should we update registers after each iteration?
> Otherwise there may be interesting effects due to swapped out pages 
> when
> running in system emulation.

I don't get this. Swapping and interruption of this code should not 
affect
the encrypted/decrypted result in memory and also not the register 
content.
But I assume that a CPACF instruction itself is some atomic operation. 
So
there needs to be a consistent state before and after the instruction. 
But
"while" the instruction is executed does not need to be consistent all 
the
time. Otherwise for example here the memory write and the update of the
registers should be atomic.

> Blocks crossing the page boundary is a similar issue, not sure if it's
> that easy to solve.

Well yes. This is a clear issue hanging around in all the memory 
read/write
crypto code here. I have no idea on how this could be solved. However, 
sounds
like there will participate a new guy in the Qemu cpacf area soon. So 
maybe
he has some ideas to work this out.

> 
> [...]