powerpc/kexec: Switch to a static PACA on the way out

With dynamic PACAs, the kexecing CPU's PACA won't lie within the kernel
static data and there is a chance that something may stomp it when preparing
to kexec.  This patch switches this final CPU to a static PACA just before
we pull the switch.

Signed-off-by: Matt Evans <matt@ozlabs.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

1 files changed, 20 insertions, 0 deletions

diff --git a/arch/powerpc/kernel/machine_kexec_64.c b/arch/powerpc/kernel/machine_kexec_64.c
index de6b70eac51d..022d2f613b7b 100644
--- a/arch/powerpc/kernel/machine_kexec_64.c
+++ b/arch/powerpc/kernel/machine_kexec_64.c
@@ -260,6 +260,12 @@ static void kexec_prepare_cpus(void)
 static union thread_union kexec_stack __init_task_data =
         { };
 
+/*
+ * For similar reasons to the stack above, the kexecing CPU needs to be on a
+ * static PACA; we switch to kexec_paca.
+ */
+struct paca_struct kexec_paca;
+
 /* Our assembly helper, in kexec_stub.S */
 extern NORET_TYPE void kexec_sequence(void *newstack, unsigned long start,
                                         void *image, void *control,
@@ -287,6 +293,20 @@ void default_machine_kexec(struct kimage *image)
         kexec_stack.thread_info.task = current_thread_info()->task;
         kexec_stack.thread_info.flags = 0;
 
+        /* We need a static PACA, too; copy this CPU's PACA over and switch to
+         * it.  Also poison per_cpu_offset to catch anyone using non-static
+         * data.
+         */
+        memcpy(&kexec_paca, get_paca(), sizeof(struct paca_struct));
+        kexec_paca.data_offset = 0xedeaddeadeeeeeeeUL;
+        paca = (struct paca_struct *)RELOC_HIDE(&kexec_paca, 0) -
+                kexec_paca.paca_index;
+        setup_paca(&kexec_paca);
+
+        /* XXX: If anyone does 'dynamic lppacas' this will also need to be
+         * switched to a static version!
+         */
+
         /* Some things are best done in assembly.  Finding globals with
          * a toc is easier in C, so pass in what we can.
          */