On Mon, 2020-10-05 at 17:43 +0100, Mark Rutland wrote: > 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@xxxxxxx> > Cc: Catalin Marinas <catalin.marinas@xxxxxxx> > Cc: James Morse <james.morse@xxxxxxx> > Cc: Will Deacon <will@xxxxxxxxxx> Reverting this commit on the top of today's linux-next fixed an issue that Thunder X2 is unable to boot: .config: https://gitlab.com/cailca/linux-mm/-/blob/master/arm64.config EFI stub: Booting Linux Kernel... EFI stub: EFI_RNG_PROTOCOL unavailable, KASLR will be disabled EFI stub: Using DTB from configuration table EFI stub: Exiting boot services and installing virtual address map... It hangs here for more than 10 minutes even with "earlycon" before I gave up. The reverting makes it boot again following by those lines almost immediately. [ 0.000000][ T0] Booting Linux on physical CPU 0x0000000000 [0x431f0af1] [ 0.000000][ T0] Linux version 5.9.0-rc8-next-20201008+ (gcc (GCC) 8.3.1 20191121 (Red Hat 8.3.1-5), GNU ld version 2.30-79.el8) #6 SMP Thu Oct 8 20:57:40 EDT 2020 [ 0.000000][ T0] efi: EFI v2.70 by American Megatrends [ 0.000000][ T0] efi: ESRT=0xf9224418 SMBIOS=0xfcca0000 SMBIOS 3.0=0xfcc90000 ACPI 2.0=0xf9720000 MEMRESERVE=0xfc965918 [ 0.000000][ T0] esrt: Reserving ESRT space from 0x00000000f9224418 to 0x00000000f9224450. [ 0.000000][ T0] ACPI: Early table checksum verification disabled [ 0.000000][ T0] ACPI: RSDP 0x00000000F9720000 000024 (v02 HPE ) [ 0.000000][ T0] ACPI: XSDT 0x00000000F9720028 0000DC (v01 HPE ServerCL 01072009 AMI 00010013) [ 0.000000][ T0] ACPI: FACP 0x00000000F9720108 000114 (v06 HPE ServerCL 01072009 AMI 00010013) [ 0.000000][ T0] ACPI: DSDT 0x00000000F9720220 000714 (v02 HPE ServerCL 20150406 INTL 20170831) [ 0.000000][ T0] ACPI: FIDT 0x00000000F9720938 00009C (v01 HPE ServerCL 01072009 AMI 00010013) ... # lscpu Architecture: aarch64 Byte Order: Little Endian CPU(s): 224 On-line CPU(s) list: 0-223 Thread(s) per core: 4 Core(s) per socket: 28 Socket(s): 2 NUMA node(s): 2 Vendor ID: Cavium Model: 1 Model name: ThunderX2 99xx Stepping: 0x1 BogoMIPS: 400.00 L1d cache: 32K L1i cache: 32K L2 cache: 256K L3 cache: 32768K NUMA node0 CPU(s): 0-111 NUMA node1 CPU(s): 112-223 Flags: fp asimd aes pmull sha1 sha2 crc32 atomics cpuid asimdrdm > --- > arch/arm64/include/asm/cpu.h | 2 ++ > arch/arm64/kernel/head.S | 3 +++ > arch/arm64/kernel/setup.c | 12 ++++++------ > arch/arm64/kernel/smp.c | 13 ++++++++----- > 4 files changed, 19 insertions(+), 11 deletions(-) > > Since v1[1]: > > * Fix typos > * Rebase atop v5.9-rc4 > > Mark. > > [1] https://lore.kernel.org/r/20200730163806.23053-1-mark.rutland@xxxxxxx > > diff --git a/arch/arm64/include/asm/cpu.h b/arch/arm64/include/asm/cpu.h > index 7faae6ff3ab4d..d9d60b18e8116 100644 > --- a/arch/arm64/include/asm/cpu.h > +++ b/arch/arm64/include/asm/cpu.h > @@ -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 */ > diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S > index 037421c66b147..2720e6ec68140 100644 > --- a/arch/arm64/kernel/head.S > +++ b/arch/arm64/kernel/head.S > @@ -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) > > diff --git a/arch/arm64/kernel/setup.c b/arch/arm64/kernel/setup.c > index 53acbeca4f574..fde4396418add 100644 > --- a/arch/arm64/kernel/setup.c > +++ b/arch/arm64/kernel/setup.c > @@ -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()); > } > @@ -281,6 +275,12 @@ u64 cpu_logical_map(int cpu) > return __cpu_logical_map[cpu]; > } > > +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; > diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c > index 355ee9eed4dde..7714310fba226 100644 > --- a/arch/arm64/kernel/smp.c > +++ b/arch/arm64/kernel/smp.c > @@ -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(); > > /*
