linux-kernel - [PATCH] arm64: set "rodata=on" as default

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Message-Id: <20241021053948.5848-1-shijie@os.amperecomputing.com>
Date: Mon, 21 Oct 2024 13:39:48 +0800
From: Huang Shijie <shijie@...amperecomputing.com>
To: catalin.marinas@....com,
	will@...nel.org
Cc: patches@...erecomputing.com,
	cl@...amperecomputing.com,
	linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	adamli@...amperecomputing.com,
	Huang Shijie <shijie@...amperecomputing.com>
Subject: [PATCH] arm64: set "rodata=on" as default

>From Documentation/admin-guide/kernel-parameters.txt, we know that:
 rodata=	[KNL,EARLY]
	on	Mark read-only kernel memory as read-only (default).
	off	Leave read-only kernel memory writable for debugging.
	full	Mark read-only kernel memory and aliases as read-only
		[arm64]

So the "rodata=on" is the default.

But the current code does not follow the document, it makes "rodata=full"
as the default.

After patch
  commit acfa60dbe038 ("arm64: mm: Fix "rodata=on" when CONFIG_RODATA_FULL_DEFAULT_ENABLED=y")
the "rodata=on" can works fine now.

The "rodata=on" can provide us more block mappings and contiguous hits
to map the linear region which minimize the TLB footprint. And the
linear aliases of pages belonging to read-only mappings in vmalloc
region are also marked as read-only now.

This patch disables RODATA_FULL_DEFAULT_ENABLED by default,
so the default value:
     rodata_full=false, rodata_enabled=true
then the default behavior follows the "rodata=on".
And we can get better performance with the "rodata=on" as the default
too.

Signed-off-by: Huang Shijie <shijie@...amperecomputing.com>
---
 arch/arm64/Kconfig | 1 -
 1 file changed, 1 deletion(-)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index fd9df6dcc593..6f30f749156e 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -1649,7 +1649,6 @@ config MITIGATE_SPECTRE_BRANCH_HISTORY
 
 config RODATA_FULL_DEFAULT_ENABLED
 	bool "Apply r/o permissions of VM areas also to their linear aliases"
-	default y
 	help
 	  Apply read-only attributes of VM areas to the linear alias of
 	  the backing pages as well. This prevents code or read-only data
-- 
2.40.1