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

[Ryan Roberts]

On 29/10/2025 10:08, 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@xxxxxxx>

This looks functionally equivalent to me, so:

Reviewed-by: Ryan Roberts <ryan.roberts@xxxxxxx>

But I don't think this tidy up is strictly necessary for your series to work?
(perhaps I'll change my mind on that as I go through it).

> ---
>  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();
>  }