Re: [PATCH v5 2/2] x86/tlb: skip redundant sync IPIs for native TLB flush

[Peter Zijlstra <peterz@infradead.org>]

On Mon, Mar 02, 2026 at 02:30:36PM +0800, Lance Yang wrote:


> @@ -221,3 +222,18 @@ NOKPROBE_SYMBOL(native_load_idt);
>  
>  EXPORT_SYMBOL(pv_ops);
>  EXPORT_SYMBOL_GPL(pv_info);
> +
> +void __init native_pv_tlb_init(void)
> +{
> +	/*
> +	 * If PV backend already set the property, respect it.
> +	 * Otherwise, check if native TLB flush sends real IPIs to all target
> +	 * CPUs (i.e., not using INVLPGB broadcast invalidation).
> +	 */
> +	if (pv_ops.mmu.flush_tlb_multi_implies_ipi_broadcast)
> +		return;
> +
> +	if (pv_ops.mmu.flush_tlb_multi == native_flush_tlb_multi &&
> +	    !cpu_feature_enabled(X86_FEATURE_INVLPGB))
> +		pv_ops.mmu.flush_tlb_multi_implies_ipi_broadcast = true;
> +}

How about making this a static_branch instead?

> diff --git a/arch/x86/include/asm/tlb.h b/arch/x86/include/asm/tlb.h
> index 866ea78ba156..87ef7147eac8 100644
> --- a/arch/x86/include/asm/tlb.h
> +++ b/arch/x86/include/asm/tlb.h
> @@ -5,10 +5,23 @@
>  #define tlb_flush tlb_flush
>  static inline void tlb_flush(struct mmu_gather *tlb);
>  
> +#define tlb_table_flush_implies_ipi_broadcast tlb_table_flush_implies_ipi_broadcast
> +static inline bool tlb_table_flush_implies_ipi_broadcast(void);
> +
>  #include <asm-generic/tlb.h>
>  #include <linux/kernel.h>
>  #include <vdso/bits.h>
>  #include <vdso/page.h>
> +#include <asm/paravirt.h>
> +
> +static inline bool tlb_table_flush_implies_ipi_broadcast(void)
> +{
> +#ifdef CONFIG_PARAVIRT
> +	return pv_ops.mmu.flush_tlb_multi_implies_ipi_broadcast;
> +#else
> +	return !cpu_feature_enabled(X86_FEATURE_INVLPGB);
> +#endif
> +}

Then this turns into:

static inline bool tlb_table_flush_implies_ipi_broadcast(void)
{
	return static_branch_likely(&tlb_ipi_broadcast_key);
}