On Wed, Mar 23, 2022 at 11:51:25AM +0000, Steve Capper wrote: > On 22/03/2022 17:56, Catalin Marinas wrote: > > At a quick look, we wouldn't have a problem with missing TLB flushing > > since huge_ptep_get_and_clear() does this for contiguous PTEs. Not sure > > why it needs this though, Steve added it in commit d8bdcff28764. I think > > we can defer this flushing to tlb_remove_page_size(). > > The TLB flush in huge_ptep_get_and_clear() was added because it was called > by hugetlb_change_protection() without any flushing. The concern was that, > without the flush, it would be possible to get to different views of the > same contiguous huge page. (Being contiguous they were not changed en masse > atomically). Maybe the code paths have been changed since but looking at hugetlb_change_protection(), we have huge_ptep_modify_prot_start() calling huge_ptep_get_and_clear() which AFAICT only needs to clear the ptes. huge_ptep_modify_prot_commit() calls set_huge_pte_at() which does another pte clearing + TLBI (clear_flush()) before setting the new ptes. So we do the pte clearing and TLBI twice already. -- Catalin
