Messages in this thread | | | From | Linus Torvalds <> | Date | Thu, 7 Nov 2019 11:54:15 -0800 | Subject | Re: [patch 5/9] x86/ioport: Reduce ioperm impact for sane usage further |
| |
On Thu, Nov 7, 2019 at 11:24 AM Brian Gerst <brgerst@gmail.com> wrote: > > Here is a different idea: We already map the TSS virtually in > cpu_entry_area. Why not page-align the IO bitmap and remap it to the > task's bitmap on task switch? That would avoid all copying on task > switch.
We map the tss _once_, statically, percpu, without ever changing it, and then we just (potentially) change a couple of fields in it on process switch.
Your idea isn't horrible, but it would involve a TLB flush for the page when the io bitmap changes. Which is almost certainly more expensive than just copying the bitmap intelligently.
Particularly since I do think that the copy can basically be done effectively never, assuming there really aren't multiple concurrent users of ioperm() (and iopl).
Linus
| |