Re: [RFC] in-kernel rseq

[Mathieu Desnoyers]

On 2026-02-24 06:16, Heiko Carstens wrote:
> On Mon, Feb 23, 2026 at 05:38:43PM +0100, Peter Zijlstra wrote:
> > This means, it needs to be woven into the asm... and I'm not that handy
> > with arm64 asm.
> >
> > The pseudo code would be something like:
> >
> > 	current->sched_seq = &_R;
> > 	...
> >
> > _start:  compute per cpu-addr
> > 	 load addr
> > 	 $OP
> > _commit: store addr
> >
> > 	...
> > 	current->sched_rseq = NULL;
> >
> >
> > Then when preemption happens (from interrupt), the instruction pointer
> > is 'simply' reset to _start and it tries again.
>
> I guess also on every interrupt, exception, and nmi current->sched_rseq needs
> to be saved on entry, and restored on exit, since other contexts can make use
> of this_cpu ops as well.

If we do a design similar to userspace rseq, we'd abort the rseq
critical section on interrupt, exception, nmi (by changing the pt_regs
instruction pointer) rather than save/restore it. This is what
userspace rseq does for signal handlers nesting on top of rseq critical
sections.

Thanks,

Mathieu

--
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com