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Message-ID: <87zfoeqoz6.fsf@mail.lhotse>
Date: Wed, 11 Sep 2024 23:50:05 +1000
From: Michael Ellerman <mpe@...erman.id.au>
To: Arnd Bergmann <arnd@...db.de>, Charlie Jenkins <charlie@...osinc.com>,
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Cc: Richard Henderson <richard.henderson@...aro.org>, Ivan Kokshaysky
 <ink@...assic.park.msu.ru>, Matt Turner <mattst88@...il.com>, Vineet Gupta
 <vgupta@...nel.org>, Russell King <linux@...linux.org.uk>, guoren
 <guoren@...nel.org>, Huacai Chen <chenhuacai@...nel.org>, WANG Xuerui
 <kernel@...0n.name>, Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
 "James E . J . Bottomley" <James.Bottomley@...senpartnership.com>, Helge
 Deller <deller@....de>, Nicholas Piggin <npiggin@...il.com>, Christophe
 Leroy <christophe.leroy@...roup.eu>, Naveen N Rao <naveen@...nel.org>,
 Alexander Gordeev <agordeev@...ux.ibm.com>, Gerald Schaefer
 <gerald.schaefer@...ux.ibm.com>, Heiko Carstens <hca@...ux.ibm.com>,
 Vasily Gorbik <gor@...ux.ibm.com>, Christian Borntraeger
 <borntraeger@...ux.ibm.com>, Sven Schnelle <svens@...ux.ibm.com>,
 Yoshinori Sato <ysato@...rs.sourceforge.jp>, Rich Felker
 <dalias@...c.org>, John Paul Adrian Glaubitz
 <glaubitz@...sik.fu-berlin.de>, "David S . Miller" <davem@...emloft.net>,
 Andreas Larsson <andreas@...sler.com>, Thomas Gleixner
 <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov
 <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
 "H. Peter Anvin" <hpa@...or.com>, Andy Lutomirski <luto@...nel.org>, Peter
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 Andrew Morton <akpm@...ux-foundation.org>, "Liam R. Howlett"
 <Liam.Howlett@...cle.com>, Vlastimil Babka <vbabka@...e.cz>, shuah
 <shuah@...nel.org>, Christoph Hellwig <hch@...radead.org>, Michal Hocko
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 Torek <chris.torek@...il.com>, Linux-Arch <linux-arch@...r.kernel.org>,
 linux-kernel@...r.kernel.org, linux-alpha@...r.kernel.org,
 linux-snps-arc@...ts.infradead.org, linux-arm-kernel@...ts.infradead.org,
 "linux-csky@...r.kernel.org" <linux-csky@...r.kernel.org>,
 loongarch@...ts.linux.dev, linux-mips@...r.kernel.org,
 linux-parisc@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
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 linux-kselftest@...r.kernel.org, linux-abi-devel@...ts.sourceforge.net
Subject: Re: [PATCH RFC v3 1/2] mm: Add personality flag to limit address to
 47 bits

"Arnd Bergmann" <arnd@...db.de> 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

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