Essentially, modern Intel processors have a design flaw that could allow malicious programs to read protected areas of a device's kernel memory (memory dedicated to the most essential core components of an operating system and their interactions with system hardware). This flaw could potentially expose protected information like passwords. Since the error is baked into the Intel x86-64 hardware, it requires an OS-level overwrite to patch - on every major operating system, including Windows, Linux, and macOS.
Because the fix entails severing kernel memory entirely from user processes, patched OSes could potentially see a massive performance hit of "five to 30 per cent slowdown, depending on the task and processor model":
These KPTI [Kernel Page Table Isolation] patches move the kernel into a completely separate address space, so it's not just invisible to a running process, it's not even there at all. Really, this shouldn't be needed, but clearly there is a flaw in Intel's silicon that allows kernel access protections to be bypassed in some way.
The downside to this separation is that it is relatively expensive, time wise, to keep switching between two separate address spaces for every system call and for every interrupt from the hardware. These context switches do not happen instantly, and they force the processor to dump cached data and reload information from memory. This increases the kernel's overhead, and slows down the computer.
Your Intel-powered machine will run slower as a result.
Five to 30 per cent is a jaw-dropping number, but because of all the secrecy right now it's difficult to tell how noticeable the impact will actually be for consumer use — enterprise-scale systems like cloud computing are likely to be the hardest hit. For the average user, it's possible that the impact will be negligible. It's also possible that a better implementation of the solution in future patches could reduce the performance hit.
"Urgent development of a software mitigation is being done in the open and recently landed in the Linux kernel" in redacted form, "and a similar mitigation began appearing in NT kernels in November," the Python Sweetness blog wrote on Monday. "In the worst case the software fix causes huge slowdowns in typical workloads ... There are hints the attack impacts common virtualization environments including Amazon EC2 and Google Compute Engine."
One problem with exploits is that even if this one is buried so deep it took ten years to find it, there's no putting the cat back in the bag post-discovery. At the very least, the tiny slice of the market running AMD processors has some grounds to feel pleased about themselves.