powerpc/64: Move paca allocation to early_setup()

The early paca and boot cpuid dance is complicated and currently does
not quite work as expected for boot cpuid != 0 cases.

early_init_devtree() currently allocates the paca_ptrs and boot cpuid
paca, but until that returns and early_setup() calls setup_paca(), this
thread is currently still executing with smp_processor_id() == 0.

One problem this causes is the paca_ptrs[smp_processor_id()] pointer is
poisoned, so valid_emergency_stack() (any backtrace) and any similar
users will crash.

Another is that the hardware id which is set here will not be returned
by get_hard_smp_processor_id(smp_processor_id()), but it would work
correctly for boot_cpuid == 0, which could lead to difficult to
reproduce or find bugs. The hard id does not seem to be used by the rest
of early_init_devtree(), it just looks like all this code might have
been put here to allocate somewhere to store boot CPU hardware id while
scanning the devtree.

Rearrange things so the hwid is put in a global variable like
boot_cpuid, and do all the paca allocation and boot paca setup in the
64-bit early_setup() after we have everything ready to go.

The paca_ptrs[0] re-poisoning code in early_setup does not seem to have
ever worked, because paca_ptrs[0] was never not-poisoned when boot_cpuid
is not 0.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
[mpe: Fix build error on 32-bit]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20221216115930.2667772-4-npiggin@gmail.com

1 files changed, 3 insertions, 9 deletions

diff --git a/arch/powerpc/kernel/prom.c b/arch/powerpc/kernel/prom.c
index 4f1c920aa13e..f318e8e1f3fe 100644
--- a/arch/powerpc/kernel/prom.c
+++ b/arch/powerpc/kernel/prom.c
@@ -370,8 +370,8 @@ static int __init early_init_dt_scan_cpus(unsigned long node,
 	    be32_to_cpu(intserv[found_thread]));
 	boot_cpuid = found;
 
-	// Pass the boot CPU's hard CPU id back to our caller
-	*((u32 *)data) = be32_to_cpu(intserv[found_thread]);
+	if (IS_ENABLED(CONFIG_PPC64))
+		boot_cpu_hwid = be32_to_cpu(intserv[found_thread]);
 
 	/*
 	 * PAPR defines "logical" PVR values for cpus that
@@ -755,7 +755,6 @@ static inline void save_fscr_to_task(void) {}
 
 void __init early_init_devtree(void *params)
 {
-	u32 boot_cpu_hwid;
 	phys_addr_t limit;
 
 	DBG(" -> early_init_devtree(%px)\n", params);
@@ -851,7 +850,7 @@ void __init early_init_devtree(void *params)
 	/* Retrieve CPU related informations from the flat tree
 	 * (altivec support, boot CPU ID, ...)
 	 */
-	of_scan_flat_dt(early_init_dt_scan_cpus, &boot_cpu_hwid);
+	of_scan_flat_dt(early_init_dt_scan_cpus, NULL);
 	if (boot_cpuid < 0) {
 		printk("Failed to identify boot CPU !\n");
 		BUG();
@@ -868,11 +867,6 @@ void __init early_init_devtree(void *params)
 
 	mmu_early_init_devtree();
 
-	// NB. paca is not installed until later in early_setup()
-	allocate_paca_ptrs();
-	allocate_paca(boot_cpuid);
-	set_hard_smp_processor_id(boot_cpuid, boot_cpu_hwid);
-
 #ifdef CONFIG_PPC_POWERNV
 	/* Scan and build the list of machine check recoverable ranges */
 	of_scan_flat_dt(early_init_dt_scan_recoverable_ranges, NULL);