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From:   Florian Fainelli <f.fainelli@gmail.com>
To:     linux-arm-kernel@vger.kernel.org
Cc:     bcm-kernel-feedback-list@Broadcom.com, ard.biesheuvel@linaro.org,
        Florian Fainelli <f.fainelli@gmail.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will.deacon@arm.com>,
        linux-arm-kernel@lists.infradead.org (moderated list:ARM64 PORT
        (AARCH64 ARCHITECTURE)), linux-kernel@vger.kernel.org (open list)
Subject: [PATCH] arm64: Allow user selection of ARM64_MODULE_PLTS
Date:   Thu, 13 Jun 2019 19:59:32 -0700
Message-Id: <20190614025932.533-1-f.fainelli@gmail.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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.
+
+	  Disabling this is usually safe for small single-platform
+	  configurations. If unsure, say y.
 
 config ARM64_PSEUDO_NMI
 	bool "Support for NMI-like interrupts"
-- 
2.17.1