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rseq: Provide static branch for time slice extensions

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Guard the time slice extension functionality with a static key, which can
be disabled on the kernel command line.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20251215155708.733429292@linutronix.de
This commit is contained in:
Thomas Gleixner
2025-12-15 17:52:06 +01:00
committed by Peter Zijlstra
parent d7a5da7a0f
commit f8380f9768
3 changed files with 33 additions and 0 deletions
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5
Documentation/admin-guide/kernel-parameters.txt
View File

@@ -6600,6 +6600,11 @@ Kernel parameters
rootflags= [KNL] Set root filesystem mount option string
rseq_slice_ext= [KNL] RSEQ based time slice extension
Format: boolean
Control enablement of RSEQ based time slice extension.
Default is 'on'.
initramfs_options= [KNL]
Specify mount options for for the initramfs mount.

11
include/linux/rseq_entry.h
View File

@@ -75,6 +75,17 @@ DECLARE_STATIC_KEY_MAYBE(CONFIG_RSEQ_DEBUG_DEFAULT_ENABLE, rseq_debug_enabled);
#define rseq_inline __always_inline
#endif
#ifdef CONFIG_RSEQ_SLICE_EXTENSION
DECLARE_STATIC_KEY_TRUE(rseq_slice_extension_key);
static __always_inline bool rseq_slice_extension_enabled(void)
{
return static_branch_likely(&rseq_slice_extension_key);
}
#else /* CONFIG_RSEQ_SLICE_EXTENSION */
static inline bool rseq_slice_extension_enabled(void) { return false; }
#endif /* !CONFIG_RSEQ_SLICE_EXTENSION */
bool rseq_debug_update_user_cs(struct task_struct *t, struct pt_regs *regs, unsigned long csaddr);
bool rseq_debug_validate_ids(struct task_struct *t);

17
kernel/rseq.c
View File

@@ -483,3 +483,20 @@ SYSCALL_DEFINE4(rseq, struct rseq __user *, rseq, u32, rseq_len, int, flags, u32
efault:
return -EFAULT;
}
#ifdef CONFIG_RSEQ_SLICE_EXTENSION
DEFINE_STATIC_KEY_TRUE(rseq_slice_extension_key);
static int __init rseq_slice_cmdline(char *str)
{
bool on;
if (kstrtobool(str, &on))
return 0;
if (!on)
static_branch_disable(&rseq_slice_extension_key);
return 1;
}
__setup("rseq_slice_ext=", rseq_slice_cmdline);
#endif /* CONFIG_RSEQ_SLICE_EXTENSION */