PTI Support To Address Meltdown Nearing The Finish Line For x86 32-bit Linux

While Page Table Isolation (PTI/KPTI) has been available since the Meltdown CPU vulnerability was disclosed at the start of the year, that's been for x86_64 Linux while the x86 32-bit support has remained a work-in-progress and only relatively recently has come together.

Joerg Roedel sent out the eighth version of the x86-32 PTI patches today, which address feedback following a good round of review. This latest page table isolation work for x86 32-bit address more developer feedback and tidies up some of the code.

It's looking like this patch series is nearing the finish line but as of writing hasn't yet been queued in any of the relevant -next branches, but wouldn't be surprised if this were to land in Linux 4.19 otherwise Linux 5.0.

We'll see, but then again it's not a high priority considering the diminishing number of people running a 32-bit x86 Linux distribution and even the shrinking number of 32-bit distros out there but will be of solace to whoever still wants to run x86 32-bit securely on CPUs vulnerable to Meltdown.

The performance impact of KPTI on x86 32-bit is likely to be significant and further slowdown this outdated hardware. It's only been since Westmere (2010, well into the x86-64 days) that PCID (Process Context Identifiers) have been supported to help offset the performance cost of PTI,