From: Yang Shi shy828301@gmail.com
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@gmail.com Suggested-by: Aneesh Kumar K.V aneesh.kumar@linux.ibm.com Signed-off-by: Yang Shi shy828301@gmail.com Acked-by: David Hildenbrand david@redhat.com Acked-by: Peter Xu peterx@redhat.com Cc: Christophe Leroy christophe.leroy@csgroup.eu Cc: Hugh Dickins hughd@google.com Cc: Jason Gunthorpe jgg@nvidia.com Cc: John Hubbard jhubbard@nvidia.com Cc: "Kirill A. Shutemov" kirill.shutemov@linux.intel.com Cc: Michael Ellerman mpe@ellerman.id.au Cc: Nicholas Piggin npiggin@gmail.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- 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;