Re: [RFC PATCH v3 13/15] context_tracking,x86: Add infrastructure to defer kernel TLBI

[Peter Zijlstra]

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.