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arm64: initialize per-cpu offsets earlier

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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: Mark 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: Will Deacon <will@kernel.org>
This commit is contained in:
Mark Rutland 2020-10-05 17:43:03 +01:00 committed by Will Deacon
parent 4dafc08d0b
commit 353e228eb3
4 changed files with 19 additions and 11 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
arch/arm64/include/asm/cpu.h
View File

@ -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 */

3
arch/arm64/kernel/head.S
View File

@ -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)

12
arch/arm64/kernel/setup.c
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@ -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;

13
arch/arm64/kernel/smp.c
View File

@ -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();
/*