3 ms·

> but syscalls per-se (outside of things like munmap) don't typically invalidate the TLB as the mapping is not changed on an user-space kernel-space transiation

by panzi 3y ago

> but syscalls per-se (outside of things like munmap) don't typically invalidate the TLB as the mapping is not changed on an user-space kernel-space transiation, only the access right Isn't that exactly what changed for the Meltdown/Spectre mitigations? That it is invalidated now?

gpderetta 3y ago
I think you are referring to KTPI, but a) it might not be needed on recent CPUs that had meltdown-like issues patched, and b) in any case on CPUs that can tag pages with process identifiers (most of them these days), it can avoid TLB flushes most of the time. But I don't claim any specific knowledge of on these mitigations.
- panzi 3y ago
  Is the PID different when entering kernel space but still doing work for the calling PID?
  - gpderetta 3y ago
    I don't think it is different, but it doesn't matter, the kernel can put whatever it wants in the register that is used to match the process identifier tag in the TLB.