On Fri, Oct 09, 2020 at 10:43:18AM +0100, Mark Rutland wrote: > Hi Qian, > > On Fri, Oct 09, 2020 at 09:51:15AM +0100, Will Deacon wrote: > > On Thu, Oct 08, 2020 at 09:18:24PM -0400, Qian Cai wrote: > > > 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 > > Sorry about this. :/ > > Will, to save you reading all the below, I think the right thing to do > for now is to revert this. > Looking at the assembly, task_cpu() gets instrumented (which puts this > patch on dodgy ground generally and I think warrants the revert), but as > it's instrumented with KASAN_INLINE that doesn't immediately explain the > issue since the shadow should be up and so we shouldn't call the report > function. I'll dig into this some more. Ok; that's my fault due to trying to do this before kasan_early_init. I see what's going on now. If you're happy to take a fixup instead of a revert, patch below. Otherwise I'll a complete patch atop of the revert after rc1. Thanks, Mark. ---->8---- >From e93fcb9649c9ccfbea9a6f17b68280420685ddc5 Mon Sep 17 00:00:00 2001 From: Mark Rutland <mark.rutland@xxxxxxx> Date: Fri, 9 Oct 2020 11:06:32 +0100 Subject: [PATCH] arm64: fix per-cpu offset initialization Qian sees a boot-time hang introduced by commit: 353e228eb355be5a ("arm64: initialize per-cpu offsets earlier") ... which happens because task_cpu() can be instrumented by KASAN, and we call init_this_cpu_offset() before we've performed the early KASAN initialization. We don't need to initialize the per-cpu offset before the early KASAN initialization runs (and we didn't prior to the patch in question), so we can avoid bothering with that. However, were task_cpu() instrumented with something else, this could cause similar issues, so let's also open-code that within init_this_cpu_offset() to avoid that possibility. It's also possible that set_my_cpu_offset() gets instrumented in future, so let's avoid that by marking it __always_inline. It's only used by init_this_cpu_offset(), so this doesn't matter for any other code. Finally, per_cpu_offset(x) is a macro expanding to __per_cpu_offset[x], which is inlined and not instrumented. Fixes: 353e228eb355be5a ("arm64: initialize per-cpu offsets earlier") Signed-off-by: Mark Rutland <mark.rutland@xxxxxxx> Reported-by: Qian Cai <cai@xxxxxxxxxx> Cc: Catalin Marinas <catalin.marinas@xxxxxxx> Cc: Will Deacon <will@xxxxxxxxxx> --- arch/arm64/include/asm/percpu.h | 2 +- arch/arm64/kernel/head.S | 2 -- arch/arm64/kernel/setup.c | 2 +- 3 files changed, 2 insertions(+), 4 deletions(-) diff --git a/arch/arm64/include/asm/percpu.h b/arch/arm64/include/asm/percpu.h index 0b6409b89e5e0..0c347d3faf55c 100644 --- a/arch/arm64/include/asm/percpu.h +++ b/arch/arm64/include/asm/percpu.h @@ -11,7 +11,7 @@ #include <asm/cmpxchg.h> #include <asm/stack_pointer.h> -static inline void set_my_cpu_offset(unsigned long off) +static __always_inline void set_my_cpu_offset(unsigned long off) { asm volatile(ALTERNATIVE("msr tpidr_el1, %0", "msr tpidr_el2, %0", diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S index e28c9d4e5278c..9bbea14a9ca3f 100644 --- a/arch/arm64/kernel/head.S +++ b/arch/arm64/kernel/head.S @@ -448,8 +448,6 @@ 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 diff --git a/arch/arm64/kernel/setup.c b/arch/arm64/kernel/setup.c index 005171972764b..161eaa83264ea 100644 --- a/arch/arm64/kernel/setup.c +++ b/arch/arm64/kernel/setup.c @@ -278,7 +278,7 @@ EXPORT_SYMBOL_GPL(cpu_logical_map); void noinstr init_this_cpu_offset(void) { - unsigned int cpu = task_cpu(current); + unsigned int cpu = current->cpu; set_my_cpu_offset(per_cpu_offset(cpu)); } -- 2.11.0
