From: Nicholas Piggin npiggin@gmail.com
[ Upstream commit 9fa24404f5044967753a6cd3e5e36f57686bec6e ]
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 npiggin@gmail.com [mpe: Fix SMP=n build as reported by sfr] Signed-off-by: Michael Ellerman mpe@ellerman.id.au Link: https://lore.kernel.org/r/20221216115930.2667772-3-npiggin@gmail.com Signed-off-by: Sasha Levin sashal@kernel.org --- 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 a0dee7354fe6b..a43865e0fb4bf 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