From: Yang Shi <shy828301@xxxxxxxxx> commit bedf03416913d88c796288f9dca109a53608c745 upstream. The IPI broadcast is used to serialize against fast-GUP, but fast-GUP will move to use RCU instead of disabling local interrupts in fast-GUP. Using an IPI is the old-styled way of serializing against fast-GUP although it still works as expected now. And fast-GUP now fixed the potential race with THP collapse by checking whether PMD is changed or not. So IPI broadcast in radix pmd collapse flush is not necessary anymore. But it is still needed for hash TLB. Link: https://lkml.kernel.org/r/20220907180144.555485-2-shy828301@xxxxxxxxx Suggested-by: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxx> Signed-off-by: Yang Shi <shy828301@xxxxxxxxx> Acked-by: David Hildenbrand <david@xxxxxxxxxx> Acked-by: Peter Xu <peterx@xxxxxxxxxx> Cc: Christophe Leroy <christophe.leroy@xxxxxxxxxx> Cc: Hugh Dickins <hughd@xxxxxxxxxx> Cc: Jason Gunthorpe <jgg@xxxxxxxxxx> Cc: John Hubbard <jhubbard@xxxxxxxxxx> Cc: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx> Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx> Cc: Nicholas Piggin <npiggin@xxxxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- arch/powerpc/mm/book3s64/radix_pgtable.c | 9 --------- 1 file changed, 9 deletions(-) --- a/arch/powerpc/mm/book3s64/radix_pgtable.c +++ b/arch/powerpc/mm/book3s64/radix_pgtable.c @@ -997,15 +997,6 @@ pmd_t radix__pmdp_collapse_flush(struct pmd = *pmdp; pmd_clear(pmdp); - /* - * pmdp collapse_flush need to ensure that there are no parallel gup - * walk after this call. This is needed so that we can have stable - * page ref count when collapsing a page. We don't allow a collapse page - * if we have gup taken on the page. We can ensure that by sending IPI - * because gup walk happens with IRQ disabled. - */ - serialize_against_pte_lookup(vma->vm_mm); - radix__flush_tlb_collapsed_pmd(vma->vm_mm, address); return pmd;
