Meltdown Protection For x86 32-bit Aligned For The Linux 4.19 Kernel
While x86_64 Linux was mitigated back in January for Meltdown, it's taken a while for x86 32-bit support for KPTI, Kernel Page Table Isolation. This is basically applying the same page table isolation approach seen on Linux x86_64 and ARM to now the 32-bit x86 kernel code. Obviously it hasn't been a priority with many Linux distributions not even bothering with i686 install images in recent years.
On Thursday, these in-development x86 32-bit PTI patches were merged to tip.git's x86/pti, now making it as part of the next PTI feature pull to the Linux kernel, which should be part of next month's Linux 4.19 kernel merge window.
With all 32-bit Intel CPUs being pre-Westmere where PCID (Process Context Identifiers) was introduced that helps with offseting the KPTI performance impact, the performance cost of (K)PTI on 32-bit Linux will potentially be quite high. I'll see about digging up some old and once popular 32-bit Intel CPUs and testing out this latest kernel code to see the impact.