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From: Richard Henderson <rth@twiddle.net>
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Date: Fri, 14 Jul 2017 14:22:30 -1000
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Subject: Re: [Qemu-devel] [PATCH v3 1/8] target/s390x: Implement CSST
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To: Aurelien Jarno <aurelien@aurel32.net>
Cc: qemu-devel@nongnu.org, david@redhat.com

On 07/14/2017 11:01 AM, Aurelien Jarno wrote:
>> +    if (parallel_cpus) {
>> +        int mask = 0;
>> +#if !defined(CONFIG_ATOMIC64)
>> +        mask = -8;
>> +#elif !defined(CONFIG_ATOMIC128)
>> +        mask = -16;
>> +#endif
>> +        if (((4 << fc) | (1 << sc)) & mask) {
>> +            cpu_loop_exit_atomic(ENV_GET_CPU(env), ra);
>> +        }
>> +    }
> 
> This doesn't look correct. For a 16-byte store, ie sc = 4, and with
> ATOMIC128 support, ie mask = -16, the condition is true.

That's WITHOUT atomic128 support that mask = -16.
If we have atomic128, then mask = 0.

>> +            if (parallel_cpus) {
>> +#ifdef CONFIG_USER_ONLY
>> +                uint32_t *haddr = g2h(a1);
>> +                ov = atomic_cmpxchg__nocheck(haddr, cv, nv);
>> +#else
>> +                TCGMemOpIdx oi = make_memop_idx(MO_TEUL | MO_ALIGN, mem_idx);
>> +                ov = helper_atomic_cmpxchgl_be_mmu(env, a1, cv, nv, oi, ra);
>> +#endif
> 
> Not a problem with the patch itself, but how complicated would it be to
> make helper_atomic_cmpxchgl_be_mmu (just like the o version) available
> also in user mode? That would make less #ifdef in the backends.

Dunno.  Probably not too bad.  I have wondered about doing that, as these sorts 
of functions are quite ugly to write.


r~