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J . Bottomley" , Helge Deller , Michael Ellerman , Nicholas Piggin , Christophe Leroy , Naveen N Rao , Alexander Gordeev , Gerald Schaefer , Heiko Carstens , Vasily Gorbik , Christian Borntraeger , Sven Schnelle , Yoshinori Sato , Rich Felker , John Paul Adrian Glaubitz , "David S . Miller" , Andreas Larsson , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , Andy Lutomirski , Peter Zijlstra , Muchun Song , Andrew Morton , "Liam R. Howlett" , Vlastimil Babka , shuah , Christoph Hellwig , Michal Hocko , "Kirill A. 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 145ezqFw 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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 Fri, Sep 06, 2024 at 07:17:44AM GMT, Arnd Bergmann wrote: > On Thu, Sep 5, 2024, at 21:15, Charlie Jenkins wrote: > > Create a personality flag ADDR_LIMIT_47BIT to support applications > > that wish to transition from running in environments that support at > > most 47-bit VAs to environments that support larger VAs. This > > personality can be set to cause all allocations to be below the 47-bit > > boundary. Using MAP_FIXED with mmap() will bypass this restriction. > > > > Signed-off-by: Charlie Jenkins > > I think having an architecture-independent mechanism to limit the size > of the 64-bit address space is useful in general, and we've discussed > the same thing for arm64 in the past, though we have not actually > reached an agreement on the ABI previously. The thread on the original proposals attests to this being rather a fraught topic, and I think the weight of opinion was more so in favour of opt-in rather than opt-out. > > > @@ -22,6 +22,7 @@ enum { > > WHOLE_SECONDS = 0x2000000, > > STICKY_TIMEOUTS = 0x4000000, > > ADDR_LIMIT_3GB = 0x8000000, > > + ADDR_LIMIT_47BIT = 0x10000000, > > }; > > I'm a bit worried about having this done specifically in the > personality flag bits, as they are rather limited. We obviously > don't want to add many more such flags when there could be > a way to just set the default limit. Since I'm the one who suggested it, I feel I should offer some kind of vague defence here :) We shouldn't let perfect be the enemy of the good. This is a relatively straightforward means of achieving the aim (assuming your concern about arch_get_mmap_end() below isn't a blocker) which has the least impact on existing code. Of course we can end up in absurdities where we start doing ADDR_LIMIT_xxBIT... but again - it's simple, shouldn't represent an egregious maintenance burden and is entirely opt-in so has things going for it. > > It's also unclear to me how we want this flag to interact with > the existing logic in arch_get_mmap_end(), which attempts to > limit the default mapping to a 47-bit address space already. How does ADDR_LIMIT_3GB presently interact with that? > > For some reason, it appears that the arch_get_mmap_end() > logic on RISC-V defaults to the maximum address > space for the 'addr==0' case which is inconsistentn with > the other architectures, so we should probably fix that > part first, possibly moving more of that logic into a > shared implementation. > > Arnd