On the reference to the SWAPGS vulnerability: the researchers in this case only tested pre-Bulldozer AMD CPUs, so it's hardly representative of modern AMD CPUs. For all we know the Zen family has the same vulnerability.
On the subject itself: really? Again? With the recent disclosure of multiple motherboard vendors having security issues this may not be as surprising, but I get the feeling that Intel has been mentioned in 90% of all articles related to security vulnerabilities in the last two years or so. They may not be the only one cutting corners, but they definitely seem to be doing it the most. You'd figure Intel would run out of things to do wrong some day but it's not today.
Based on external and internal analysis, AMD believes it is not vulnerable to the SWAPGS variant attacks because AMD products are designed not to speculate on the new GS value following a speculative SWAPGS.
This is pretty clear language.