>процессоры AMD данной атаке не подвержены

В оригинальной бумаге по Meltdown:

"However, we did not manage
to successfully leak kernel memory with the attack de-
scribed in Section 5, neither on ARM nor on AMD. The
reasons for this can be manifold. First of all, our im-
plementation might simply be too slow and a more opti-
mized version might succeed. For instance, a more shal-
low out-of-order execution pipeline could tip the race
condition towards against the data leakage. Similarly,
if the processor lacks certain features, e.g., no re-order
buffer, our current implementation might not be able to
leak data. However, for both ARM and AMD, the toy
example as described in Section 3 works reliably, indi-
cating that out-of-order execution generally occurs and
instructions past illegal memory accesses are also per-
formed.

Т.е. дыра в процессорах AMD есть, но авторы поленились написать эксплоит, а AMD решили не чесаться пока эксплоит не напишут. И неизвестно, что хуже т.к. Intel рано или поздно дыру залатают, а для AMD цирк ещё впереди.