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(p200300cbc70107002393b0f4ef08bd51.dip0.t-ipconnect.de. [2003:cb:c701:700:2393:b0f4:ef08:bd51]) by smtp.gmail.com with ESMTPSA id o3-20020adfeac3000000b0020c66310845sm2016448wrn.55.2022.05.11.09.30.59 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 11 May 2022 09:31:00 -0700 (PDT) Message-ID: Date: Wed, 11 May 2022 18:30:59 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.8.0 Subject: Re: [PATCH v8 06/23] mm/shmem: Handle uffd-wp special pte in page fault handler Content-Language: en-US To: Peter Xu , linux-kernel@vger.kernel.org, linux-mm@kvack.org Cc: Mike Kravetz , Nadav Amit , Matthew Wilcox , Mike Rapoport , Hugh Dickins , Jerome Glisse , "Kirill A . Shutemov" , Andrea Arcangeli , Andrew Morton , Axel Rasmussen , Alistair Popple References: <20220405014646.13522-1-peterx@redhat.com> <20220405014844.14239-1-peterx@redhat.com> From: David Hildenbrand Organization: Red Hat In-Reply-To: <20220405014844.14239-1-peterx@redhat.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > +/* > + * This is actually a page-missing access, but with uffd-wp special pte > + * installed. It means this pte was wr-protected before being unmapped. > + */ > +static vm_fault_t pte_marker_handle_uffd_wp(struct vm_fault *vmf) > +{ > + /* > + * Just in case there're leftover special ptes even after the region > + * got unregistered - we can simply clear them. We can also do that > + * proactively when e.g. when we do UFFDIO_UNREGISTER upon some uffd-wp > + * ranges, but it should be more efficient to be done lazily here. > + */ > + if (unlikely(!userfaultfd_wp(vmf->vma) || vma_is_anonymous(vmf->vma))) > + return pte_marker_clear(vmf); What would happen if we do a unregister followed by a register? IMHO we should start with a clean uffd-wp slate then. Your comment makes ma assume that we could receive stale WP events, which would be wrong? -- Thanks, David / dhildenb