On 3/9/26 03:07, Lance Yang wrote: > From: Lance Yang <[email protected]> > > Enable the optimization introduced in the previous patch for x86.
Best to make the patch description standalone, not referring to "previous patch". > > native_pv_tlb_init() checks whether native_flush_tlb_multi() is in use. > On CONFIG_PARAVIRT systems, it checks pv_ops; on non-PARAVIRT, native > flush is always in use. > > It decides once at boot whether to enable the optimization: if using > native TLB flush and INVLPGB is not supported, we know IPIs were sent > and can skip the redundant sync. The decision is fixed via a static > key as Peter suggested[1]. > > PV backends (KVM, Xen, Hyper-V) typically have their own implementations > and don't call native_flush_tlb_multi() directly, so they cannot be trusted > to provide the IPI guarantees we need. > > Two-step plan as David suggested[2]: > > Step 1 (this patch): Skip redundant sync when we're 100% certain the TLB > flush sent IPIs. INVLPGB is excluded because when supported, we cannot > guarantee IPIs were sent, keeping it clean and simple. > > Step 2 (future work): Send targeted IPIs only to CPUs actually doing > software/lockless page table walks, benefiting all architectures. > > Regarding Step 2, it obviously only applies to setups where Step 1 does > not apply: like x86 with INVLPGB or arm64. > > [1] > https://lore.kernel.org/linux-mm/[email protected]/ > [2] > https://lore.kernel.org/linux-mm/[email protected]/ > > Suggested-by: Peter Zijlstra <[email protected]> > Suggested-by: David Hildenbrand (Arm) <[email protected]> > Signed-off-by: Lance Yang <[email protected]> > --- [...] > static inline void tlb_flush(struct mmu_gather *tlb) > { > unsigned long start = 0UL, end = TLB_FLUSH_ALL; > @@ -20,7 +30,12 @@ static inline void tlb_flush(struct mmu_gather *tlb) > end = tlb->end; > } > > - flush_tlb_mm_range(tlb->mm, start, end, stride_shift, > tlb->freed_tables); > + /* > + * Pass both freed_tables and unshared_tables so that lazy-TLB CPUs > + * also receive IPIs during unsharing page tables. "unsharing of page tables" ? I would maybe have it written ass "Treat unshared_tables just like freed_tables, such that lazy-TLB CPUs also receive IPIs during unsharing of page tables, allowing us to safely implement tlb_table_flush_implies_ipi_broadcast()." > + */ > + flush_tlb_mm_range(tlb->mm, start, end, stride_shift, > + tlb->freed_tables || tlb->unshared_tables); > } In general, LGTM. Acked-by: David Hildenbrand (Arm) <[email protected]> -- Cheers, David
