Commit 353e228e authored by Mark Rutland's avatar Mark Rutland Committed by Will Deacon
Browse files

arm64: initialize per-cpu offsets earlier 



The current initialization of the per-cpu offset register is difficult
to follow and this initialization is not always early enough for
upcoming instrumentation with KCSAN, where the instrumentation callbacks
use the per-cpu offset.

To make it possible to support KCSAN, and to simplify reasoning about
early bringup code, let's initialize the per-cpu offset earlier, before
we run any C code that may consume it. To do so, this patch adds a new
init_this_cpu_offset() helper that's called before the usual
primary/secondary start functions. For consistency, this is also used to
re-initialize the per-cpu offset after the runtime per-cpu areas have
been allocated (which can change CPU0's offset).

So that init_this_cpu_offset() isn't subject to any instrumentation that
might consume the per-cpu offset, it is marked with noinstr, preventing
instrumentation.

Signed-off-by: default avatarMark Rutland <mark.rutland@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: James Morse <james.morse@arm.com>
Cc: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20201005164303.21389-1-mark.rutland@arm.com


Signed-off-by: default avatarWill Deacon <will@kernel.org>
parent 4dafc08d

arch/arm64/include/asm/cpu.h

+2 −0
Original line number Diff line number Diff line
@@ -68,4 +68,6 @@ void __init init_cpu_features(struct cpuinfo_arm64 *info); 
void update_cpu_features(int cpu, struct cpuinfo_arm64 *info,

				 struct cpuinfo_arm64 *boot);



void init_this_cpu_offset(void);



#endif /* __ASM_CPU_H */

arch/arm64/kernel/head.S

+3 −0
Original line number Diff line number Diff line
@@ -452,6 +452,8 @@ SYM_FUNC_START_LOCAL(__primary_switched) 
	bl	__pi_memset

	dsb	ishst				// Make zero page visible to PTW



	bl	init_this_cpu_offset



#ifdef CONFIG_KASAN

	bl	kasan_early_init

#endif
@@ -758,6 +760,7 @@ SYM_FUNC_START_LOCAL(__secondary_switched) 
	ptrauth_keys_init_cpu x2, x3, x4, x5

#endif



	bl	init_this_cpu_offset

	b	secondary_start_kernel

SYM_FUNC_END(__secondary_switched)

arch/arm64/kernel/setup.c

+6 −6
Original line number Diff line number Diff line
@@ -87,12 +87,6 @@ void __init smp_setup_processor_id(void) 
	u64 mpidr = read_cpuid_mpidr() & MPIDR_HWID_BITMASK;

	set_cpu_logical_map(0, mpidr);



	/*

	 * clear __my_cpu_offset on boot CPU to avoid hang caused by

	 * using percpu variable early, for example, lockdep will

	 * access percpu variable inside lock_release

	 */

	set_my_cpu_offset(0);

	pr_info("Booting Linux on physical CPU 0x%010lx [0x%08x]\n",

		(unsigned long)mpidr, read_cpuid_id());

}
@@ -282,6 +276,12 @@ u64 cpu_logical_map(int cpu) 
}

EXPORT_SYMBOL_GPL(cpu_logical_map);



void noinstr init_this_cpu_offset(void)

{

	unsigned int cpu = task_cpu(current);

	set_my_cpu_offset(per_cpu_offset(cpu));

}



void __init __no_sanitize_address setup_arch(char **cmdline_p)

{

	init_mm.start_code = (unsigned long) _text;

arch/arm64/kernel/smp.c

+8 −5
Original line number Diff line number Diff line
@@ -192,10 +192,7 @@ asmlinkage notrace void secondary_start_kernel(void) 
	u64 mpidr = read_cpuid_mpidr() & MPIDR_HWID_BITMASK;

	struct mm_struct *mm = &init_mm;

	const struct cpu_operations *ops;

	unsigned int cpu;



	cpu = task_cpu(current);

	set_my_cpu_offset(per_cpu_offset(cpu));

	unsigned int cpu = smp_processor_id();



	/*

	 * All kernel threads share the same mm context; grab a
@@ -435,7 +432,13 @@ void __init smp_cpus_done(unsigned int max_cpus) 


void __init smp_prepare_boot_cpu(void)

{

	set_my_cpu_offset(per_cpu_offset(smp_processor_id()));

	/*

	 * Now that setup_per_cpu_areas() has allocated the runtime per-cpu

	 * areas it is only safe to read the CPU0 boot-time area, and we must

	 * reinitialize the offset to point to the runtime area.

	 */

	init_this_cpu_offset();



	cpuinfo_store_boot_cpu();



	/*

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