From: "Arnd Bergmann" <arnd@arndb.de>
To: "Dmitry Rokosov" <ddrokosov@sberdevices.ru>
Cc: "Neil Armstrong" <neil.armstrong@linaro.org>,
"Alexey Romanov" <avromanov@sberdevices.ru>,
"Rob Herring" <robh+dt@kernel.org>,
krzysztof.kozlowski+dt@linaro.org,
"Kevin Hilman" <khilman@baylibre.com>,
jbrunet@baylibre.com, martin.blumenstingl@googlemail.com,
"Linus Walleij" <linus.walleij@linaro.org>,
devicetree@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
linux-amlogic@lists.infradead.org, linux-kernel@vger.kernel.org,
kernel@sberdevices.ru
Subject: Re: [PATCH v1 0/3] Meson A1 32-bit support
Date: Mon, 27 Feb 2023 17:15:58 +0100 [thread overview]
Message-ID: <a5fa8b23-4ec8-475f-be5e-538b53d6f82d@app.fastmail.com> (raw)
In-Reply-To: <20230227155100.hhl4yvkyfqfyoa6h@CAB-WSD-L081021>
On Mon, Feb 27, 2023, at 16:51, Dmitry Rokosov wrote:
> On Mon, Feb 27, 2023 at 03:58:50PM +0100, Arnd Bergmann wrote:
>>
>> I would argue that is a problem with buildroot, and using a 32-bit
>> kernel is not something we should encourage over fixing buildroot
>> to do it right, or building the kernel separately from the rootfs.
>>
>> We do allow building support for a couple of ARMv8 SoCs in 32-bit
>> mode, but that is usually because they ship with a 32-bit bootrom
>> and cannot actually run a 64-bit kernel.
>
> To be honest, I didn't know about this principle. It looks like a very
> rational approach "start from max supported bitness".
> Based on overall maintainers opinion, we have to prepare a patch for
> buildroot to support compat mode :)
That would be great, thanks a lot!
For what it's worth, the main arguments in favor of running a 64-bit
kernel with compat user space over a 32-bit kernel are support for:
- larger RAM sizes without highmem (most 32-bit kernels only
support 768MB of lowmem, and highmem sucks)
- larger virtual address space (4GB vs 3GB or less)
- CPU specific errata workarounds (arch/arm/ only has those for 32-bit cpus)
- mitigations for common attacks such as spectre
- security hardening that depends on larger address space
(KASLR, BTI, ptrauth, PAN, ...)
- emulating instructions that were removed in Armv8 (setend, swp, ...)
Most of these don't apply in userspace, so the incentive to
run smaller 32-bit userland on systems with less than 1GB of
RAM usually outweighs the benefits of 64-bit userspace.
Arnd
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next prev parent reply other threads:[~2023-02-27 16:17 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-02-22 11:50 [PATCH v1 0/3] Meson A1 32-bit support Alexey Romanov
2023-02-22 11:50 ` [PATCH v1 1/3] meson: pinctrl: use CONFIG_PINCTRL_A1 with CONFIG_ARM Alexey Romanov
2023-03-06 13:45 ` Linus Walleij
2023-03-06 13:49 ` neil.armstrong
2023-03-06 13:52 ` Linus Walleij
2023-02-22 11:50 ` [PATCH v1 2/3] firmware: meson: use CONFIG_MESON_SM " Alexey Romanov
2023-02-22 11:50 ` [PATCH v1 3/3] arch/arm: dts: introduce meson-a1 device tree Alexey Romanov
2023-02-23 9:08 ` Krzysztof Kozlowski
2023-02-23 9:09 ` Krzysztof Kozlowski
2023-02-27 14:39 ` Dmitry Rokosov
2023-02-27 14:41 ` Krzysztof Kozlowski
2023-02-27 8:15 ` [PATCH v1 0/3] Meson A1 32-bit support neil.armstrong
2023-02-27 14:28 ` Dmitry Rokosov
2023-02-27 14:46 ` neil.armstrong
2023-02-27 16:01 ` Dmitry Rokosov
2023-02-27 14:58 ` Arnd Bergmann
2023-02-27 15:51 ` Dmitry Rokosov
2023-02-27 16:15 ` Arnd Bergmann [this message]
2023-02-27 16:37 ` Dmitry Rokosov
2023-02-27 16:38 ` Neil Armstrong
2023-02-27 16:50 ` Dmitry Rokosov
2023-02-27 18:19 ` Arnd Bergmann
2023-02-28 8:49 ` Dmitry Rokosov
2023-03-09 21:52 ` Kevin Hilman
2023-03-10 15:20 ` Dmitry Rokosov
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