From: Will Deacon <will.deacon@arm.com>
To: Florian Fainelli <f.fainelli@gmail.com>
Cc: ard.biesheuvel@linaro.org,
Catalin Marinas <catalin.marinas@arm.com>,
open list <linux-kernel@vger.kernel.org>,
bcm-kernel-feedback-list@Broadcom.com,
linux-arm-kernel@vger.kernel.org,
"moderated list:ARM64 PORT \(AARCH64 ARCHITECTURE\)"
<linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH] arm64: Allow user selection of ARM64_MODULE_PLTS
Date: Mon, 17 Jun 2019 18:32:41 +0100 [thread overview]
Message-ID: <20190617173241.GM30800@fuggles.cambridge.arm.com> (raw)
In-Reply-To: <20190614025932.533-1-f.fainelli@gmail.com>
On Thu, Jun 13, 2019 at 07:59:32PM -0700, Florian Fainelli wrote:
> Make ARM64_MODULE_PLTS a selectable Kconfig symbol, since some people
> might have very big modules spilling out of the dedicated module area
> into vmalloc. Help text is copied from the ARM 32-bit counterpart.
>
> Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
> ---
> arch/arm64/Kconfig | 14 +++++++++++++-
> 1 file changed, 13 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 697ea0510729..36befe987b73 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -1418,8 +1418,20 @@ config ARM64_SVE
> KVM in the same kernel image.
>
> config ARM64_MODULE_PLTS
> - bool
> + bool "Use PLTs to allow module memory to spill over into vmalloc area"
> select HAVE_MOD_ARCH_SPECIFIC
> + help
> + Allocate PLTs when loading modules so that jumps and calls whose
> + targets are too far away for their relative offsets to be encoded
> + in the instructions themselves can be bounced via veneers in the
> + module's PLT. This allows modules to be allocated in the generic
> + vmalloc area after the dedicated module memory area has been
> + exhausted. The modules will use slightly more memory, but after
> + rounding up to page size, the actual memory footprint is usually
> + the same.
Isn't the worry really about the runtime performance overhead introduced
by the veneers, as opposed to the memory usage of the module?
> + Disabling this is usually safe for small single-platform
> + configurations. If unsure, say y.
So should this be on by default?
Will
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next prev parent reply other threads:[~2019-06-17 17:32 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-06-14 2:59 [PATCH] arm64: Allow user selection of ARM64_MODULE_PLTS Florian Fainelli
2019-06-14 7:02 ` Ard Biesheuvel
2019-06-17 17:32 ` Will Deacon [this message]
2019-06-17 18:03 ` Florian Fainelli
2019-06-17 18:10 ` Will Deacon
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