From: Catalin Marinas <catalin.marinas@arm.com>
To: Arnd Bergmann <arnd@arndb.de>
Cc: Linux ARM <linux-arm-kernel@lists.infradead.org>,
Gregory CLEMENT <gregory.clement@bootlin.com>,
Russell King - ARM Linux admin <linux@armlinux.org.uk>,
Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Subject: Re: [PATCH v2 1/6] ARM: Use PAGE_SIZE for ELF_EXEC_PAGESIZE
Date: Fri, 12 Jun 2020 12:50:08 +0100 [thread overview]
Message-ID: <20200612115007.GB19739@gaia> (raw)
In-Reply-To: <CAK8P3a2BpNVSE86zEYSGd7x+OF-7spjGmU331TbQX=DRAkpMoQ@mail.gmail.com>
On Fri, Jun 12, 2020 at 10:46:17AM +0200, Arnd Bergmann wrote:
> On Fri, Jun 12, 2020 at 10:35 AM Russell King - ARM Linux admin
> <linux@armlinux.org.uk> wrote:
> > On Fri, Jun 12, 2020 at 10:22:17AM +0200, Arnd Bergmann wrote:
> > > On Thu, Jun 11, 2020 at 3:49 PM Gregory CLEMENT
> > > <gregory.clement@bootlin.com> wrote:
> > > >
> > > > Currently ELF_EXEC_PAGESIZE is 4096 which is also the page size. In
> > > > order to be able to use other size of page than 4K, use PAGE_SIZE
> > > > instead of the hardcoded value.
> > > >
> > > > The use of PAGE_SIZE will be also aligned with what we find in other
> > > > architectures such as arm64.
> > > >
> > > > This is inspired from fa0ca2726ea9 ("DSMP 64K support") and
> > > > 4ef803e12baf ("mmu: large-page: Added support for multiple kernel page
> > > > sizes") from
> > > > https://github.com/MarvellEmbeddedProcessors/linux-marvell.git
> > > >
> > > > Signed-off-by: Gregory CLEMENT <gregory.clement@bootlin.com>
> > >
> > > IIRC using page sizes above 16KB here also requires using a
> > > non-ancient linker in user space that places sections on
> > > ELF_EXEC_PAGESIZE boundaries, right?
>
> Correction: I was thinking of SHMLBA, not ELF_EXEC_PAGESIZE.
> SHMLBA is defined to 16KB in arch/arm/ at the moment (based on 4K
> page size), or (4 * PAGE_SIZE) on arm64, which can blow up to 256KB.
>
> AFAICT, SHMLBA should now be defined as "min(16384, PAGE_SIZE)".
Good point. We should do this with the COMPAT_SHMLBA on arm64 (we didn't
bother since COMPAT had a dependency on 4K but you can override it with
EXPERT).
> > Doesn't that mean that this change breaks all existing userspace when
> > ELF_EXEC_PAGESIZE is not 4k?
>
> I think a lot of older user space would be broken with page sizes larger
> than 16KB, but would still work with 8KB or 16KB. Larger page sizes
> would only work with user space that was linked in the last five years
> or so, using a toolchain that has the workarounds for running on arm64
> with 64KB page size.
FWIW, Debian armhf now boots fine on an arm64 kernel with 64K pages (it
wasn't the case some years ago).
--
Catalin
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next prev parent reply other threads:[~2020-06-12 11:50 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-11 13:49 [PATCH v2 0/6] ARM: Add support for large kernel page (from 8K to 64K) Gregory CLEMENT
2020-06-11 13:49 ` [PATCH v2 1/6] ARM: Use PAGE_SIZE for ELF_EXEC_PAGESIZE Gregory CLEMENT
2020-06-12 8:22 ` Arnd Bergmann
2020-06-12 8:35 ` Russell King - ARM Linux admin
2020-06-12 8:46 ` Arnd Bergmann
2020-06-12 8:50 ` Russell King - ARM Linux admin
2020-06-12 11:50 ` Catalin Marinas [this message]
2020-06-12 12:06 ` Gregory CLEMENT
2020-06-12 8:52 ` Gregory CLEMENT
2020-06-11 13:49 ` [PATCH v2 2/6] ARM: pagetable: prepare hardware page table to use large page Gregory CLEMENT
2020-06-11 13:49 ` [PATCH v2 3/6] ARM: Make the number of fix bitmap depend on the page size Gregory CLEMENT
2020-06-11 13:49 ` [PATCH v2 4/6] ARM: mm: Aligned pte allocation to one page Gregory CLEMENT
2020-06-12 8:37 ` Arnd Bergmann
2020-06-12 10:25 ` Catalin Marinas
2020-06-12 11:56 ` Gregory CLEMENT
2020-06-11 13:49 ` [PATCH v2 5/6] ARM: Add large kernel page support Gregory CLEMENT
2020-06-11 13:49 ` [PATCH v2 6/6] ARM: Add 64K page support at MMU level Gregory CLEMENT
2020-06-11 16:21 ` [PATCH v2 0/6] ARM: Add support for large kernel page (from 8K to 64K) Russell King - ARM Linux admin
2020-06-12 9:15 ` Gregory CLEMENT
2020-06-12 9:23 ` Arnd Bergmann
2020-06-12 12:21 ` Catalin Marinas
2020-06-12 12:49 ` Arnd Bergmann
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