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Fri, 6 Sep 2024 05:56:02 -0400 (EDT) X-Mailer: MessagingEngine.com Webmail Interface X-Mailing-List: linuxppc-dev@lists.ozlabs.org List-Id: List-Help: List-Post: List-Subscribe: , , List-Unsubscribe: MIME-Version: 1.0 Date: Fri, 06 Sep 2024 09:55:42 +0000 From: "Arnd Bergmann" To: guoren Cc: "Charlie Jenkins" , "Richard Henderson" , "Ivan Kokshaysky" , "Matt Turner" , "Vineet Gupta" , "Russell King" , "Huacai Chen" , "WANG Xuerui" , "Thomas Bogendoerfer" , "James E . 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" , "Lorenzo Stoakes" , 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 Message-Id: In-Reply-To: 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> Subject: Re: [PATCH RFC v3 1/2] mm: Add personality flag to limit address to 47 bits Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable On Fri, Sep 6, 2024, at 09:14, Guo Ren wrote: > On Fri, Sep 6, 2024 at 3:18=E2=80=AFPM Arnd Bergmann w= rote: >> >> 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. > > To optimize RISC-V progress, I recommend: > > Step 1: Approve the patch. > Step 2: Update Go and OpenJDK's RISC-V backend to utilize it. > Step 3: Wait approximately several iterations for Go & OpenJDK > Step 4: Remove the 47-bit constraint in arch_get_mmap_end() I really want to first see a plausible explanation about why RISC-V can't just implement this using a 47-bit DEFAULT_MAP_WINDOW like all the other major architectures (x86, arm64, powerpc64), e.g. something like the patch below (untested, probably slightly wrong but show illustrate my point). Arnd diff --git a/arch/riscv/include/asm/processor.h b/arch/riscv/include/asm= /processor.h index 8702b8721a27..de9863be1efd 100644 --- a/arch/riscv/include/asm/processor.h +++ b/arch/riscv/include/asm/processor.h @@ -20,17 +20,8 @@ * mmap_end < addr, being mmap_end the top of that address space. * See Documentation/arch/riscv/vm-layout.rst for more details. */ -#define arch_get_mmap_end(addr, len, flags) \ -({ \ - unsigned long mmap_end; \ - typeof(addr) _addr =3D (addr); \ - if ((_addr) =3D=3D 0 || is_compat_task() || \ - ((_addr + len) > BIT(VA_BITS - 1))) \ - mmap_end =3D STACK_TOP_MAX; \ - else \ - mmap_end =3D (_addr + len); \ - mmap_end; \ -}) +#define arch_get_mmap_end(addr, len, flags) \ + (((addr) > DEFAULT_MAP_WINDOW) ? TASK_SIZE : DEFAULT_MAP_WINDOW) =20 #define arch_get_mmap_base(addr, base) \ ({ \ @@ -47,7 +38,7 @@ }) =20 #ifdef CONFIG_64BIT -#define DEFAULT_MAP_WINDOW (UL(1) << (MMAP_VA_BITS - 1)) +#define DEFAULT_MAP_WINDOW (is_compat_task() ? (UL(1) << (MMAP_VA_B= ITS - 1)) : TASK_SIZE_32) #define STACK_TOP_MAX TASK_SIZE_64 #else #define DEFAULT_MAP_WINDOW TASK_SIZE