linux-kernel - [PATCH v3 07/59] x86: Sanitize linker script

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Message-ID: <20220915111143.614728935@infradead.org>
Date:   Thu, 15 Sep 2022 13:10:46 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     linux-kernel@...r.kernel.org, peterz@...radead.org, x86@...nel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        Andrew Cooper <Andrew.Cooper3@...rix.com>,
        Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
        Johannes Wikner <kwikner@...z.ch>,
        Alyssa Milburn <alyssa.milburn@...ux.intel.com>,
        Jann Horn <jannh@...gle.com>, "H.J. Lu" <hjl.tools@...il.com>,
        Joao Moreira <joao.moreira@...el.com>,
        Joseph Nuzman <joseph.nuzman@...el.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Juergen Gross <jgross@...e.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        K Prateek Nayak <kprateek.nayak@....com>,
        Eric Dumazet <edumazet@...gle.com>
Subject: [PATCH v3 07/59] x86: Sanitize linker script

From: Thomas Gleixner <tglx@...utronix.de>

The section ordering in the text section is more than suboptimal:

    ALIGN_ENTRY_TEXT_BEGIN
    ENTRY_TEXT
    ALIGN_ENTRY_TEXT_END
    SOFTIRQENTRY_TEXT
    STATIC_CALL_TEXT
    INDIRECT_THUNK_TEXT

ENTRY_TEXT is in a seperate PMD so it can be mapped into the cpu entry area
when KPTI is enabled. That means the sections after it are also in a
seperate PMD. That's wasteful especially as the indirect thunk text is a
hotpath on retpoline enabled systems and the static call text is fairly hot
on 32bit.

Move the entry text section last so that the other sections share a PMD
with the text before it. This is obviously just best effort and not
guaranteed when the previous text is just at a PMD boundary.

The text section placement needs an overhaul in general. There is e.g. no
point to have debugfs, sysfs, cpuhotplug and other rarely used functions
next to hot path text.

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 arch/x86/kernel/vmlinux.lds.S |   13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -132,18 +132,19 @@ SECTIONS
 		CPUIDLE_TEXT
 		LOCK_TEXT
 		KPROBES_TEXT
-		ALIGN_ENTRY_TEXT_BEGIN
-		ENTRY_TEXT
-		ALIGN_ENTRY_TEXT_END
 		SOFTIRQENTRY_TEXT
-		STATIC_CALL_TEXT
-		*(.gnu.warning)
-
 #ifdef CONFIG_RETPOLINE
 		__indirect_thunk_start = .;
 		*(.text.__x86.*)
 		__indirect_thunk_end = .;
 #endif
+		STATIC_CALL_TEXT
+
+		ALIGN_ENTRY_TEXT_BEGIN
+		ENTRY_TEXT
+		ALIGN_ENTRY_TEXT_END
+		*(.gnu.warning)
+
 	} :text =0xcccc
 
 	/* End of text section, which should occupy whole number of pages */