Re: [RFC][PATCH v2 5/5] sched: User Mode Concurency Groups

On Mon, Jan 24, 2022 at 11:03:06AM +0100, Peter Zijlstra wrote:

quoted

Either way, it looks like we'd need helpers along the lines of:

| static __always_inline void umcg_enter_from_user(struct pt_regs *regs)
| {
| 	if (current->flags & PF_UMCG_WORKER)
| 		umcg_sys_enter(regs, -1);
| }
| 
| static __always_inline void umcg_exit_to_user(struct pt_regs *regs)
| {
| 	if (current->flags & PF_UMCG_WORKER)
| 		umcg_sys_exit(regs);
| }

Would something like:

#ifndef arch_irqentry_irq_enter
static __always_inline bool arch_irqentry_irq_enter(struct pt_regs *regs)
{
	if (!regs_irqs_disabled(regs)) {
		local_irq_enable();
		return true;
	}
	return false;
}
#endif

static __always_inline void irqentry_irq_enter(struct pt_regs *regs)
{
	if (arch_irqentry_irq_inherit(regs)) {
		if (user_mode(regs) && (current->flags & PF_UMCG_WORKER))
			umcg_sys_enter(regs, -1);
	}
}

Work? Then arm64 can do:

static __always_inline bool arch_irqentry_irq_enter(struct pt_regs *regs)
{
	local_daif_inherit();
	return interrupts_enabled(regs);
}

or somesuch...

Ah,.. just read your other email, so your concern is about the
user_mode() thing due to ARM64 taking a different exception path for
from-user vs from-kernel ?

I don't mind too much if arm64 decides to open-code the umcg hooks, but
please do it such that's hard to forget a spot.