On Mon, 9 Dec 2024 13:12:49 +0100 Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote: > On Mon, Dec 09, 2024 at 01:04:43PM +0100, Valentin Schneider wrote: > > > > But I wonder what exactly was the original scenario encountered by > > > Valentin. I mean, if TLB entry invalidations were necessary to sync > > > changes to kernel text after flipping a static branch, then it might be > > > less overhead to make a list of affected pages and call INVLPG on them. > > No; TLB is not involved with text patching (on x86). > > > > Valentin, do you happen to know? > > > > So from my experimentation (hackbench + kernel compilation on housekeeping > > CPUs, dummy while(1) userspace loop on isolated CPUs), the TLB flushes only > > occurred from vunmap() - mainly from all the hackbench threads coming and > > going. > > Right, we have virtually mapped stacks. Wait... Are you talking about the kernel stac? But that's only 4 pages (or 8 pages with KASAN), so that should be easily handled with INVLPG. No CR4 dances are needed for that. What am I missing? Petr T
