Re: [PATCH v3 02/13] x86/xen: simplify flush_lazy_mmu()

[Dave Hansen]

On 10/15/25 01:27, Kevin Brodsky wrote:
> While at it, we can also avoid preempt_disable() if we are not
> in lazy MMU mode - xen_get_lazy_mode() should tolerate preemption.
...
>  static void xen_flush_lazy_mmu(void)
>  {
> -	preempt_disable();
> -
>  	if (xen_get_lazy_mode() == XEN_LAZY_MMU) {
> -		arch_leave_lazy_mmu_mode();
> -		arch_enter_lazy_mmu_mode();
> +		preempt_disable();
> +		xen_mc_flush();
> +		preempt_enable();
>  	}

But xen_get_lazy_mode() does:

	this_cpu_read(xen_lazy_mode);

Couldn't preemption end up doing the 'xen_lazy_mode' read and the
xen_mc_flush() on different CPUs?

That seems like a problem. Is there a reason it's safe?