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 lzPU2vsP 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000104, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Feb 18, 2025 at 01:12:05PM +0100, Vlastimil Babka wrote: > On 2/13/25 19:16, Lorenzo Stoakes wrote: > > The guard regions feature was initially implemented to support anonymous > > mappings only, excluding shmem. > > > > This was done such as to introduce the feature carefully and incrementally > > and to be conservative when considering the various caveats and corner > > cases that are applicable to file-backed mappings but not to anonymous > > ones. > > > > Now this feature has landed in 6.13, it is time to revisit this and to > > extend this functionality to file-backed and shmem mappings. > > > > In order to make this maximally useful, and since one may map file-backed > > mappings read-only (for instance ELF images), we also remove the > > restriction on read-only mappings and permit the establishment of guard > > regions in any non-hugetlb, non-mlock()'d mapping. > > Do you plan to address mlock later too? I guess somebody might find use for > those. Is there some fundamental issue or just that we need to define some > good semantics for corner cases? (i.e. if pages are already populated in the > mlocked area, discarding them by replacing with guard pte's goes against > that, so do we allow it or not?). Yeah that's the fundamental issue with mlock, it does not interact with the zapping part of MADV_GUARD_INSTALL, and that is why we disallow it (but not so for MADV_GUARD_REMOVE, as if a VMA that contains guard regions is locked _afterwards_ there will be no zapping). We could potentially expose an equivalent, as there are for other flags, a _LOCKED variant of the madvise() flag, like MADV_GUARD_INSTALL_LOCKED to make this explicit. That is probably the most sensible option, if there is a need for this! > > Otherwise nice discussion of all the potential issues here! > Thanks! :)