Re: [PATCH] mm/mmu_notifier: Remove non_block_start/end() from notifier invocation

[Sean Christopherson <seanjc@google.com>]

On Wed, Aug 12, 2026, David Woodhouse wrote:
> On Tue, 2026-08-11 at 15:58 -0700, Sean Christopherson wrote:
> > On Tue, Aug 11, 2026, David Woodhouse wrote:
> > > On Tue, 2026-08-11 at 22:21 +0200, Paolo Bonzini wrote:
> > > > 
> > > > for_each_present_cpu(cpu)
> > > >     if (per_cpu(kvm_gpc_reader, cpu) == gpc)
> > > >         cpumask_set_cpu(cpu, gpc_readers);
> > > > __kvm_kick_many_cpus(cpus, wait);
> > > 
> > > 
> > > I'm literally sitting here watching you reinvent what SRCU already does.
> > 
> > The problem, for me at least, is that SRCU does this and a _lot_ more.
> > 
> > > Which, again, is *fine* given the behaviour of *these* read-side sections.
> > 
> > Well, yeah.  Why use a nailgun to put a nail into the wall to hang a picture
> > frame? (other than the indisputable fact that power tools are fun). 
> 
> It's not a nailgun, it's a drill. And in this analogy, my observation
> that it works absolutely fine for us with *these* SRCU read-side users
> ... is equivalent to finding the torque setting that lets you put it
> into screwdriver mode.

Yeah, but my concern is that there are KVM users out there that will put the
drill into hammer drill mode, likely unknowingly, and then complain that "we"
put a hole in their wall.

What I want is a strong guarantee that the user can't configure bad torque/mode
settings, even unintentionally.