Commit f8380f97 authored by Thomas Gleixner's avatar Thomas Gleixner Committed by Peter Zijlstra
Browse files

rseq: Provide static branch for time slice extensions 



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

Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20251215155708.733429292@linutronix.de
parent d7a5da7a

Documentation/admin-guide/kernel-parameters.txt

+5 −0
Original line number Diff line number Diff line
@@ -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.

include/linux/rseq_entry.h

+11 −0
Original line number Diff line number Diff line
@@ -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);

kernel/rseq.c

+17 −0
Original line number Diff line number Diff line
@@ -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 */