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 wkxwx/W+ 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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 Tue, Feb 18, 2025 at 06:25:35PM +0100, David Hildenbrand wrote: > > > > > > QEMU, for example, will issue an mlockall(MCL_CURRENT | MCL_FUTURE); when > > > requested to then exit(); if it fails. > > > > Hm under what circumstances? I use qemu extensively to test this stuff with > > no issues. Unless you mean it's using it in the 'host' code somehow. > > > -overcommit mem-lock=on > > or (legacy) > > -realtime mlock=on > > I think. > > [...] Thanks > > > > > > > > > It fails because it tries to 'touch' the memory, but 'touching' guard > > > > region memory causes a segfault. This kind of breaks the idea of > > > > mlock()'ing guard regions. > > > > > > > > I think adding workarounds to make this possible in any way is not really > > > > worth it (and would probably be pretty gross). > > > > > > > > We already document that 'mlock()ing lightweight guard regions will fail' > > > > as per man page so this is all in line with that. > > > > > > Right, and I claim that supporting VM_LOCKONFAULT might likely be as easy as > > > allowing install/remove of guard regions when that flag is set. > > > > We already allow this flag! VM_LOCKED and VM_HUGETLB are the only flags we > > disallow. > > > See mlock2(); > > SYSCALL_DEFINE3(mlock2, unsigned long, start, size_t, len, int, flags) > { > vm_flags_t vm_flags = VM_LOCKED; > > if (flags & ~MLOCK_ONFAULT) > return -EINVAL; > > if (flags & MLOCK_ONFAULT) > vm_flags |= VM_LOCKONFAULT; > > return do_mlock(start, len, vm_flags); > } > > > VM_LOCKONFAULT always as VM_LOCKED set as well. OK cool, that makes sense. As with much kernel stuff, I knew this in the past. Then I forgot. Then I knew again, then... :P if only somebody would write it down in a book... Yeah then that makes sense to check explicitly for (VM_LOCKED | VM_LOCKONFAULT) in any MADV_GUARD_INSTALL_LOCKED variant as obviously this would be passively excluded right now. > > -- > Cheers, > > David / dhildenb >