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 0jmbIhIJ 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 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: List-Subscribe: List-Unsubscribe: On Sun, Oct 20, 2024 at 07:37:54PM +0200, Florian Weimer wrote: > * Lorenzo Stoakes: > > > Early testing of the prototype version of this code suggests a 5 times > > speed up in memory mapping invocations (in conjunction with use of > > process_madvise()) and a 13% reduction in VMAs on an entirely idle android > > system and unoptimised code. > > > > We expect with optimisation and a loaded system with a larger number of > > guard pages this could significantly increase, but in any case these > > numbers are encouraging. > > > > This way, rather than having separate VMAs specifying which parts of a > > range are guard pages, instead we have a VMA spanning the entire range of > > memory a user is permitted to access and including ranges which are to be > > 'guarded'. > > > > After mapping this, a user can specify which parts of the range should > > result in a fatal signal when accessed. > > > > By restricting the ability to specify guard pages to memory mapped by > > existing VMAs, we can rely on the mappings being torn down when the > > mappings are ultimately unmapped and everything works simply as if the > > memory were not faulted in, from the point of view of the containing VMAs. > > We have a glibc (so not Android) dynamic linker bug that asks us to > remove PROT_NONE mappings in mapped shared objects: > > Extra struct vm_area_struct with ---p created when PAGE_SIZE < max-page-size > > > It's slightly different from a guard page because our main goal is to > avoid other mappings to end up in those gaps, which has been shown to > cause odd application behavior in cases where it happens. If I > understand the series correctly, the kernel would not automatically > attribute those PROT_NONE gaps to the previous or subsequent mapping. > We would have to extend one of the surrounding mapps and apply > MADV_POISON to that over-mapped part. That doesn't seem too onerous. > > Could the ELF loader in the kernel do the same thing for the main > executable and the program loader? Currently this implementation is only available for private anonymous memory. We may look at extending it to shmem and file-backed memory in the future but there are a whole host of things to overcome to make that work so it's one step at a time! :)