[PATCH v4 02/12] x86/xen: simplify flush_lazy_mmu()

[David Hildenbrand]

On 29.10.25 11:08, Kevin Brodsky wrote:
> arch_flush_lazy_mmu_mode() is called when outstanding batched
> pgtable operations must be completed immediately. There should
> however be no need to leave and re-enter lazy MMU completely. The
> only part of that sequence that we really need is xen_mc_flush();
> call it directly.
> 
> Signed-off-by: Kevin Brodsky <kevin.brodsky at arm.com>
> ---
>   arch/x86/xen/mmu_pv.c | 6 ++----
>   1 file changed, 2 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/xen/mmu_pv.c b/arch/x86/xen/mmu_pv.c
> index 2a4a8deaf612..7a35c3393df4 100644
> --- a/arch/x86/xen/mmu_pv.c
> +++ b/arch/x86/xen/mmu_pv.c
> @@ -2139,10 +2139,8 @@ 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();
> -	}
> +	if (xen_get_lazy_mode() == XEN_LAZY_MMU)
> +		xen_mc_flush();
>   
>   	preempt_enable();
>   }

Looks like that was moved to XEN code in

commit a4a7644c15096f57f92252dd6e1046bf269c87d8
Author: Juergen Gross <jgross at suse.com>
Date:   Wed Sep 13 13:38:27 2023 +0200

     x86/xen: move paravirt lazy code


And essentially the previous implementation lived in 
arch/x86/kernel/paravirt.c:paravirt_flush_lazy_mmu(void) in an 
implementation-agnostic way:

void paravirt_flush_lazy_mmu(void)
{
        preempt_disable();

        if (paravirt_get_lazy_mode() == PARAVIRT_LAZY_MMU) {
                arch_leave_lazy_mmu_mode();
                arch_enter_lazy_mmu_mode();
        }

        preempt_enable();
}


So indeed, I assume just doing the flush here is sufficient.

Reviewed-by: David Hildenbrand <david at redhat.com>

-- 
Cheers

David / dhildenb