> It is not, but if like it was the case for rowhammer, it was linked to a specific instruction (clflush).

No, rowhammer does not need clflush. All rowhammer needs is to be able to write to the same physical memory locations repeatedly. Normally the cache would get in the way, so the attacker needs to bypass it. Flushing the cache (clflush) is one way, but there are others; AFAIK, it has been demonstrated rowhammer from within a Javascript VM, which has no access to clflush.