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x86: Sanitize linker script 

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@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20220915111143.614728935@infradead.org
This commit is contained in:
Thomas Gleixner 2022-09-15 13:10:46 +02:00 committed by Peter Zijlstra
parent b26d66f8da
commit 24a9c543d2
1 changed files with 7 additions and 6 deletions
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13
arch/x86/kernel/vmlinux.lds.S
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@ -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 */