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dmarc=pass (policy=none) header.from=arm.com; spf=pass (imf03.hostedemail.com: domain of Steve.Capper@arm.com designates 40.107.13.81 as permitted sender) smtp.mailfrom=Steve.Capper@arm.com X-Stat-Signature: 7f1u6nxupxib4wo6sgwn7gngd6mxyh5d X-HE-Tag: 1648053292-334928 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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. Cheers, -- Steve