On Wed, Mar 23, 2022 at 04:34:26PM +0000, Steve Capper wrote: > > > On 23/03/2022 16:21, Catalin Marinas wrote: > > 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. > > > > Thanks, yeah indeed the code has changed and the flush should be removed > from the arm64 huge_ptep_get_and_clear. Did anybody send a patch for this? Will
