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J . Bottomley" , Helge Deller , 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. Shutemov" , Chris Torek , Linux-Arch , linux-kernel@vger.kernel.org, linux-alpha@vger.kernel.org, linux-snps-arc@lists.infradead.org, linux-arm-kernel@lists.infradead.org, "linux-csky@vger.kernel.org" , loongarch@lists.linux.dev, linux-mips@vger.kernel.org, linux-parisc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, linux-sh@vger.kernel.org, sparclinux@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org, linux-abi-devel@lists.sourceforge.net Subject: Re: [PATCH RFC v3 1/2] mm: Add personality flag to limit address to 47 bits In-Reply-To: <89d21669-8daa-4225-b6d2-33d439ebd746@app.fastmail.com> References: <20240905-patches-below_hint_mmap-v3-0-3cd5564efbbb@rivosinc.com> <20240905-patches-below_hint_mmap-v3-1-3cd5564efbbb@rivosinc.com> <9fc4746b-8e9d-4a75-b966-e0906187e6b7@app.fastmail.com> <58f39d58-579e-4dd3-8084-baebf86f1ae0@lucifer.local> <7be08ea9-f343-42da-805f-e5f0d61bde26@app.fastmail.com> <016c7857-9ea8-4333-96e6-3ae3870f375f@lucifer.local> <89d21669-8daa-4225-b6d2-33d439ebd746@app.fastmail.com> Date: Wed, 11 Sep 2024 23:50:05 +1000 Message-ID: <87zfoeqoz6.fsf@mail.lhotse> X-Mailing-List: linuxppc-dev@lists.ozlabs.org List-Id: List-Help: List-Post: List-Subscribe: , , List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain "Arnd Bergmann" writes: > On Mon, Sep 9, 2024, at 23:22, Charlie Jenkins wrote: >> On Fri, Sep 06, 2024 at 10:52:34AM +0100, Lorenzo Stoakes wrote: >>> On Fri, Sep 06, 2024 at 09:14:08AM GMT, Arnd Bergmann wrote: >>> The intent is to optionally be able to run a process that keeps higher bits >>> free for tagging and to be sure no memory mapping in the process will >>> clobber these (correct me if I'm wrong Charlie! :) ... > Let's see what the other architectures do and then come up with > a way that fixes the pointer tagging case first on those that are > broken. We can see if there needs to be an extra flag after that. > Here is what I found: > > - x86_64 uses DEFAULT_MAP_WINDOW of BIT(47), uses a 57 bit > address space when an addr hint is passed. > - arm64 uses DEFAULT_MAP_WINDOW of BIT(47) or BIT(48), returns > higher 52-bit addresses when either a hint is passed or > CONFIG_EXPERT and CONFIG_ARM64_FORCE_52BIT is set (this > is a debugging option) > - ppc64 uses a DEFAULT_MAP_WINDOW of BIT(47) or BIT(48), > returns 52 bit address when an addr hint is passed It's 46 or 47 depending on PAGE_SIZE (4K or 64K): $ git grep "define DEFAULT_MAP_WINDOW_USER64" arch/powerpc/include/asm/task_size_64.h arch/powerpc/include/asm/task_size_64.h:#define DEFAULT_MAP_WINDOW_USER64 TASK_SIZE_128TB arch/powerpc/include/asm/task_size_64.h:#define DEFAULT_MAP_WINDOW_USER64 TASK_SIZE_64TB cheers