From: Catalin Marinas <catalin.marinas@arm•com>
To: Charlie Jenkins <charlie@rivosinc•com>
Cc: "Liam R. Howlett" <Liam.Howlett@oracle•com>,
Arnd Bergmann <arnd@arndb•de>, guoren <guoren@kernel•org>,
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Subject: Re: [PATCH RFC v3 1/2] mm: Add personality flag to limit address to 47 bits
Date: Fri, 13 Sep 2024 11:08:23 +0100 [thread overview]
Message-ID: <ZuQPF7Gbcqzq0U6N@arm.com> (raw)
In-Reply-To: <ZuNaD+zAXiAulc0n@ghost>
On Thu, Sep 12, 2024 at 02:15:59PM -0700, Charlie Jenkins wrote:
> On Thu, Sep 12, 2024 at 11:53:49AM +0100, Catalin Marinas wrote:
> > On Wed, Sep 11, 2024 at 11:18:12PM -0700, Charlie Jenkins wrote:
> > > Opting-in to the higher address space is reasonable. However, it is not
> > > my preference, because the purpose of this flag is to ensure that
> > > allocations do not exceed 47-bits, so it is a clearer ABI to have the
> > > applications that want this guarantee to be the ones setting the flag,
> > > rather than the applications that want the higher bits setting the flag.
> >
> > Yes, this would be ideal. Unfortunately those applications don't know
> > they need to set a flag in order to work.
>
> It's not a regression, the applications never worked (on platforms that
> do not have this default). The 47-bit default would allow applications
> that didn't work to start working at the cost of a non-ideal ABI. That
> doesn't seem like a reasonable tradeoff to me. If applications want to
> run on new hardware that has different requirements, shouldn't they be
> required to update rather than expect the kernel will solve their
> problems for them?
That's a valid point but it depends on the application and how much you
want to spend updating user-space. OpenJDK is fine, if you need a JIT
you'll have to add support for that architecture anyway. But others are
arch-agnostic, you just recompile to your target. It's not an ABI
problem, more of an API one.
The x86 case (and powerpc/arm64) was different, the 47-bit worked for a
long time before expanding it. So it made a lot of sense to keep the
same default.
Anyway, the prctl() can go both ways, either expanding or limiting the
default address space. So I'd be fine with such interface.
--
Catalin
next prev parent reply other threads:[~2024-09-13 10:08 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-09-05 21:15 [PATCH RFC v3 0/2] mm: Introduce ADDR_LIMIT_47BIT personality flag Charlie Jenkins
2024-09-05 21:15 ` [PATCH RFC v3 1/2] mm: Add personality flag to limit address to 47 bits Charlie Jenkins
2024-09-06 6:59 ` Michael Ellerman
2024-09-09 19:07 ` Charlie Jenkins
2024-09-10 9:20 ` Christophe Leroy
2024-09-10 12:43 ` Geert Uytterhoeven
2024-09-11 13:38 ` Michael Ellerman
2024-09-12 6:20 ` Charlie Jenkins
2024-09-20 5:10 ` Michael Ellerman
2024-09-11 13:37 ` Michael Ellerman
2024-09-06 7:17 ` Arnd Bergmann
2024-09-06 8:02 ` Lorenzo Stoakes
2024-09-06 8:14 ` Lorenzo Stoakes
2024-09-06 9:14 ` Arnd Bergmann
2024-09-06 9:52 ` Lorenzo Stoakes
2024-09-09 23:22 ` Charlie Jenkins
2024-09-10 9:13 ` Arnd Bergmann
2024-09-10 23:29 ` Charlie Jenkins
2024-09-11 13:50 ` Michael Ellerman
2024-09-06 9:14 ` Guo Ren
2024-09-06 9:55 ` Arnd Bergmann
2024-09-06 11:43 ` Catalin Marinas
2024-09-10 19:08 ` Liam R. Howlett
2024-09-11 0:45 ` Charlie Jenkins
2024-09-11 7:25 ` Arnd Bergmann
2024-09-12 6:06 ` Charlie Jenkins
2024-09-11 18:21 ` Catalin Marinas
2024-09-12 6:18 ` Charlie Jenkins
2024-09-12 10:53 ` Catalin Marinas
2024-09-12 21:15 ` Charlie Jenkins
2024-09-13 10:08 ` Catalin Marinas [this message]
2024-09-13 10:21 ` Catalin Marinas
2024-09-13 20:15 ` Charlie Jenkins
2024-09-13 7:41 ` Lorenzo Stoakes
2024-09-13 21:04 ` Charlie Jenkins
2024-10-02 14:26 ` Palmer Dabbelt
2024-09-05 21:15 ` [PATCH RFC v3 2/2] selftests/mm: Create ADDR_LIMIT_47BIT test Charlie Jenkins
2024-09-06 6:08 ` [PATCH RFC v3 0/2] mm: Introduce ADDR_LIMIT_47BIT personality flag Guo Ren
2024-09-06 6:19 ` John Paul Adrian Glaubitz
2024-09-08 11:26 ` Jiaxun Yang
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