Re: [PATCH 4/7] x86/xen: support nested lazy_mmu sections (again)

[Alexander Gordeev <agordeev@linux.ibm.com>]

On Thu, Sep 04, 2025 at 01:57:33PM +0100, Kevin Brodsky wrote:
...
> -static void xen_enter_lazy_mmu(void)
> +static lazy_mmu_state_t xen_enter_lazy_mmu(void)
>  {
> +	if (this_cpu_read(xen_lazy_mode) == XEN_LAZY_MMU)
> +		return LAZY_MMU_NESTED;
> +
>  	enter_lazy(XEN_LAZY_MMU);
> +	return LAZY_MMU_DEFAULT;
>  }
>  
>  static void xen_flush_lazy_mmu(void)
> @@ -2167,11 +2171,12 @@ static void __init xen_post_allocator_init(void)
>  	pv_ops.mmu.write_cr3 = &xen_write_cr3;
>  }
>  
> -static void xen_leave_lazy_mmu(void)
> +static void xen_leave_lazy_mmu(lazy_mmu_state_t state)
>  {
>  	preempt_disable();
>  	xen_mc_flush();
> -	leave_lazy(XEN_LAZY_MMU);
> +	if (state != LAZY_MMU_NESTED)
> +		leave_lazy(XEN_LAZY_MMU);

Based on xen_enter_lazy_mmu(), whether this condition needs to be
executed with the preemption disabled?

Or may be this_cpu_read(xen_lazy_mode) + enter_lazy(XEN_LAZY_MMU)
should be executed with the preemption disabled?

>  	preempt_enable();
>  }

Thanks!