[Skiboot] [PATCH v2 5/7] Disable attn instruction on boot

[Michael Neuling]

Currently we don't touch the attn enable bit in HID0 on boot.

When attn is enabled, it's available everywhere including HV=0.  This
is very dangerous for the host kernel.

This explicitly disables the attn instruction on all CPUs on boot.

Signed-off-by: Michael Neuling <mikey at neuling.org>
---
 core/cpu.c    | 16 ++++++++++++++++
 core/init.c   |  2 ++
 include/cpu.h |  1 +
 3 files changed, 19 insertions(+)

diff --git a/core/cpu.c b/core/cpu.c
index d113d77..1611562 100644
--- a/core/cpu.c
+++ b/core/cpu.c
@@ -408,6 +408,15 @@ static void enable_attn(void)
 	set_hid0(hid0);
 }
 
+static void disable_attn(void)
+{
+	unsigned long hid0;
+
+	hid0 = mfspr(SPR_HID0);
+	hid0 &= ~SPR_HID0_ENABLE_ATTN;
+	set_hid0(hid0);
+}
+
 extern void __trigger_attn(void);
 void trigger_attn(void)
 {
@@ -415,6 +424,12 @@ void trigger_attn(void)
 	__trigger_attn();
 }
 
+void init_hid(void)
+{
+	/* attn is enabled even when HV=0, so make sure it's off */
+	disable_attn();
+}
+
 void pre_init_boot_cpu(void)
 {
 	struct cpu_thread *cpu = this_cpu();
@@ -481,6 +496,7 @@ void init_boot_cpu(void)
 	init_cpu_thread(boot_cpu, cpu_state_active, pir);
 	init_boot_tracebuf(boot_cpu);
 	assert(this_cpu() == boot_cpu);
+	init_hid();
 
 	list_head_init(&global_job_queue);
 }
diff --git a/core/init.c b/core/init.c
index 15fff18..a72972d 100644
--- a/core/init.c
+++ b/core/init.c
@@ -809,6 +809,8 @@ void __noreturn __secondary_cpu_entry(void)
 	/* Secondary CPU called in */
 	cpu_callin(cpu);
 
+	init_hid();
+
 	/* Wait for work to do */
 	while(true) {
 		int i;
diff --git a/include/cpu.h b/include/cpu.h
index 9eaf59c..587cd52 100644
--- a/include/cpu.h
+++ b/include/cpu.h
@@ -120,6 +120,7 @@ static inline void __nomcount cpu_relax(void)
 void pre_init_boot_cpu(void);
 void init_boot_cpu(void);
 void init_all_cpus(void);
+void init_hid(void);
 
 /* This brings up our secondaries */
 extern void cpu_bringup(void);
-- 
2.7.4