Re: [PATCH 5/6] powerpc/livepatch: Add livepatch stack to struct thread_info

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At this point ti->livepatch_sp points to the next CPUs thread_info for softirq_ctx?

Sorry I'm not sure what you mean.

None of this relates to the current CPUs thread info.

Oh! I meant that klp_init_thread_info points to the end of (struct thread_info {} + 1) in the stack of the thread/task, but with the irq_contexts they are a separate array and not on stack

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diff --git a/arch/powerpc/kernel/setup_64.c b/arch/powerpc/kernel/setup_64.c
index 3807fb05b6de..1b6cabb8e715 100644
--- a/arch/powerpc/kernel/setup_64.c
+++ b/arch/powerpc/kernel/setup_64.c

@@ -69,6 +69,7 @@
 #include <asm/kvm_ppc.h>
 #include <asm/hugetlb.h>
 #include <asm/epapr_hcalls.h>
+#include <asm/livepatch.h>
 
 #ifdef DEBUG
 #define DBG(fmt...) udbg_printf(fmt)

@@ -667,16 +668,16 @@ static void __init emergency_stack_init(void)
 	limit = min(safe_stack_limit(), ppc64_rma_size);
 
 	for_each_possible_cpu(i) {
-		unsigned long sp;
-		sp  = memblock_alloc_base(THREAD_SIZE, THREAD_SIZE, limit);
-		sp += THREAD_SIZE;
-		paca[i].emergency_sp = __va(sp);
+		struct thread_info *ti;
+		ti = __va(memblock_alloc_base(THREAD_SIZE, THREAD_SIZE, limit));
+		klp_init_thread_info(ti);
+		paca[i].emergency_sp = (void *)ti + THREAD_SIZE;

 
Does emergency_sp still end up 128 byte aligned after this?

It should end up THREAD_SIZE aligned as before, due to the memblock_alloc_base().

Yep.. I missed it.. so where is the space for ti? The stack is going to go grow downwards from ti+THREAD_SIZE

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 #ifdef CONFIG_PPC_BOOK3S_64
 		/* emergency stack for machine check exception handling. */
-		sp  = memblock_alloc_base(THREAD_SIZE, THREAD_SIZE, limit);
-		sp += THREAD_SIZE;
-		paca[i].mc_emergency_sp = __va(sp);
+		ti = __va(memblock_alloc_base(THREAD_SIZE, THREAD_SIZE, limit));
+		klp_init_thread_info(ti);

Do we care about live-patching in this context? Are we mixing per-thread and per-cpu contexts?

Well we probably don't want to be doing live patching when we're on the
emergency stacks. But we have no control over whether that happens so we have
to support it.

OK.. I was wondering if the code will even work.. I wonder if the ftrace data structures will work in real mode, including the hash/etc.

Balbir