Re: [PATCH v2 02/30] include/exec/memop: Add bits describing atomicity

[Alex Bennée]

Richard Henderson <richard.henderson@linaro.org> writes:

> These bits may be used to describe the precise atomicity
> requirements of the guest, which may then be used to
> constrain the methods by which it may be emulated by the host.
>
> For instance, the AArch64 LDP (32-bit) instruction changes
> semantics with ARMv8.4 LSE2, from
>
>   MO_64 | MO_ATMAX_4 | MO_ATOM_IFALIGN
>   (64-bits, single-copy atomic only on 4 byte units,
>    nonatomic if not aligned by 4),
>
> to
>
>   MO_64 | MO_ATMAX_SIZE | MO_ATOM_WITHIN16
>   (64-bits, single-copy atomic within a 16 byte block)
>
> The former may be implemented with two 4 byte loads, or
> a single 8 byte load if that happens to be efficient on
> the host.  The latter may not, and may also require a
> helper when misaligned.
>
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>

-- 
Alex Bennée
Virtualisation Tech Lead @ Linaro