Safari takes a performance hit in the iOS 11.2 update to gain Spectre attack protection

Just as promised, Apple released a new, 11.2.2 update for iOS that will patch the Safari browser used on its iPhones and iPads from the Spectre vulnerability, adding to the Meltdown patch in 11.2.

Apple warned that the update may slow Safari down a bit, as you can see in the excerpt below, but those gaping chip vulnerabilities that are raging this season aren't ones you can afford to stay open against.

The JetStream test Apple is referring to is a JavaScript benchmark that probes performance in "the most advanced web applications," but still it is unlikely that it will notice the difference in your daily interactions with an iPhone. Scrolling feels much faster in iOS 11 compared to previous editions anyway, so those two percentage points of slowdown or so, will likely go unnoticed.

source: Apple