From 9fa24404f5044967753a6cd3e5e36f57686bec6e Mon Sep 17 00:00:00 2001 From: Nicholas Piggin Date: Fri, 16 Dec 2022 21:59:28 +1000 Subject: powerpc/64: Fix task_cpu in early boot when booting non-zero cpuid powerpc/64 can boot on a non-zero SMP processor id. Initially, the boot CPU is said to be "assumed to be 0" until early_init_devtree() discovers the id from the device tree. That is not a good description because the assumption can be wrong and that has to be handled, the better description is that 0 is used as a placeholder, and things are fixed after the real id is discovered. smp_processor_id() is set to the boot cpuid, but task_cpu(current) is not, which causes the smp_processor_id() == task_cpu(current) invariant to be broken until init_idle() in sched_init(). This is quite fragile and could lead to subtle bugs in future. One bug is that validate_sp_size uses task_cpu() to get the process stack, so any stack trace from the booting CPU between early_init_devtree() and sched_init() will have problems. Early on paca_ptrs[0] will be poisoned, so that can cause machine checks dereferencing that memory in real mode. Later, validating the current stack pointer against the idle task of a different secondary will probably cause no stack trace to be printed. Fix this by setting thread_info->cpu right after smp_processor_id() is set to the boot cpuid. Signed-off-by: Nicholas Piggin [mpe: Fix SMP=n build as reported by sfr] Signed-off-by: Michael Ellerman Link: https://lore.kernel.org/r/20221216115930.2667772-3-npiggin@gmail.com --- arch/powerpc/kernel/setup_64.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/arch/powerpc/kernel/setup_64.c b/arch/powerpc/kernel/setup_64.c index a0dee7354fe6..a43865e0fb4b 100644 --- a/arch/powerpc/kernel/setup_64.c +++ b/arch/powerpc/kernel/setup_64.c @@ -396,6 +396,11 @@ void __init early_setup(unsigned long dt_ptr) } fixup_boot_paca(paca_ptrs[boot_cpuid]); setup_paca(paca_ptrs[boot_cpuid]); /* install the paca into registers */ + // smp_processor_id() now reports boot_cpuid + +#ifdef CONFIG_SMP + task_thread_info(current)->cpu = boot_cpuid; // fix task_cpu(current) +#endif /* * Configure exception handlers. This include setting up trampolines -- cgit