psci: fix error due to a non zero context id

In the previous psci implementation, the psci_afflvl_power_on_finish()
function would run into an error condition if the value of the context
id parameter in the cpu_on and cpu_suspend psci calls was != 0. The
parameter was being restored as the return value of the affinity level
0 finisher function. A non zero context id would be treated as an
error condition. This would prevent successful wake up of the cpu from
a power down state. Also, the contents of the general purpose
registers were not being cleared upon return to the non-secure world
after a cpu power up. This could potentially allow the non-secure
world to view secure data.

This patch ensures that all general purpose registers are set to ~0
prior to the final eret that drops the execution to the non-secure
world. The context id is used to initialize the general purpose
register x0 prior to re-entry into the non-secure world and is no
longer restored as a function return value. A platform helper
(platform_get_stack()) has been introduced to facilitate this change.

Change-Id: I2454911ffd75705d6aa8609a5d250d9b26fa097c

10 files changed, 64 insertions, 16 deletions

diff --git a/common/psci/psci_afflvl_on.c b/common/psci/psci_afflvl_on.c
index 7126b98..c118cab 100644
--- a/common/psci/psci_afflvl_on.c
+++ b/common/psci/psci_afflvl_on.c
@@ -337,7 +337,7 @@ static unsigned int psci_afflvl0_on_finish(unsigned long mpidr,
 	 * for restoring the re-entry info
 	 */
 	index = cpu_node->data;
-	rc = psci_get_ns_entry_info(index);
+	psci_get_ns_entry_info(index);
 
 	/* Clean caches before re-entering normal world */
 	dcsw_op_louis(DCCSW);
diff --git a/common/psci/psci_afflvl_suspend.c b/common/psci/psci_afflvl_suspend.c
index b68b4df..05b0aad 100644
--- a/common/psci/psci_afflvl_suspend.c
+++ b/common/psci/psci_afflvl_suspend.c
@@ -389,7 +389,7 @@ static unsigned int psci_afflvl0_suspend_finish(unsigned long mpidr,
 	 * information that we had stashed away during the suspend
 	 * call to set this cpu on it's way.
 	 */
-	rc = psci_get_ns_entry_info(index);
+	psci_get_ns_entry_info(index);
 
 	/* Clean caches before re-entering normal world */
 	dcsw_op_louis(DCCSW);
diff --git a/common/psci/psci_common.c b/common/psci/psci_common.c
index 59126ba..8eb0213 100644
--- a/common/psci/psci_common.c
+++ b/common/psci/psci_common.c
@@ -36,6 +36,7 @@
 #include <platform.h>
 #include <psci.h>
 #include <psci_private.h>
+#include <runtime_svc.h>
 
 /*******************************************************************************
  * Arrays that contains information needs to resume a cpu's execution when woken
@@ -280,9 +281,10 @@ unsigned int psci_calculate_affinity_state(aff_map_node *aff_node)
  * resume a cpu's execution in the non-secure state after it has been physically
  * powered on i.e. turned ON or resumed from SUSPEND
  ******************************************************************************/
-unsigned int psci_get_ns_entry_info(unsigned int index)
+void psci_get_ns_entry_info(unsigned int index)
 {
 	unsigned long sctlr = 0, scr, el_status, id_aa64pfr0;
+	gp_regs *ns_gp_regs;
 
 	scr = read_scr();
 
@@ -318,10 +320,22 @@ unsigned int psci_get_ns_entry_info(unsigned int index)
 
 	/* Fulfill the cpu_on entry reqs. as per the psci spec */
 	write_scr(scr);
-	write_spsr(psci_ns_entry_info[index].eret_info.spsr);
 	write_elr(psci_ns_entry_info[index].eret_info.entrypoint);
 
-	return psci_ns_entry_info[index].context_id;
+	/*
+	 * Set the general purpose registers to ~0 upon entry into the
+	 * non-secure world except for x0 which should contain the
+	 * context id & spsr. This is done directly on the "would be"
+	 * stack pointer. Prior to entry into the non-secure world, an
+	 * offset equivalent to the size of the 'gp_regs' structure is
+	 * added to the sp. This general purpose register context is
+	 * retrieved then.
+	 */
+	ns_gp_regs = (gp_regs *) platform_get_stack(read_mpidr());
+	ns_gp_regs--;
+	memset(ns_gp_regs, ~0, sizeof(*ns_gp_regs));
+	ns_gp_regs->x0 = psci_ns_entry_info[index].context_id;
+	ns_gp_regs->spsr = psci_ns_entry_info[index].eret_info.spsr;
 }
 
 /*******************************************************************************
diff --git a/common/psci/psci_entry.S b/common/psci/psci_entry.S
index 2f39f36..74cdf95 100644
--- a/common/psci/psci_entry.S
+++ b/common/psci/psci_entry.S
@@ -32,6 +32,7 @@
 #include <platform.h>
 #include <psci.h>
 #include <psci_private.h>
+#include <runtime_svc.h>
 #include <asm_macros.S>
 
 	.globl	psci_aff_on_finish_entry
@@ -77,7 +78,6 @@ psci_aff_common_finish_entry:
 	mov	x0, x19
 	mov	x1, #MPIDR_AFFLVL0
 	blr	x22
-	mov	x21, x0
 
 	/* --------------------------------------------
 	 * Give ourselves a stack allocated in Normal
@@ -88,10 +88,13 @@ psci_aff_common_finish_entry:
 	bl	platform_set_stack
 
 	/* --------------------------------------------
-	 * Restore the context id. value
+	 * Use the size of the general purpose register
+	 * context to restore the register state
+	 * stashed by earlier code
 	 * --------------------------------------------
 	 */
-	mov	x0, x21
+	sub	sp, sp, #SIZEOF_GPREGS
+	exception_exit	restore_regs
 
 	/* --------------------------------------------
 	 * Jump back to the non-secure world assuming
diff --git a/common/psci/psci_private.h b/common/psci/psci_private.h
index 4741397..e2100f8 100644
--- a/common/psci/psci_private.h
+++ b/common/psci/psci_private.h
@@ -108,7 +108,7 @@ extern int get_max_afflvl(void);
 extern unsigned int psci_get_phys_state(unsigned int);
 extern unsigned int psci_get_aff_phys_state(aff_map_node *);
 extern unsigned int psci_calculate_affinity_state(aff_map_node *);
-extern unsigned int psci_get_ns_entry_info(unsigned int index);
+extern void psci_get_ns_entry_info(unsigned int index);
 extern unsigned long mpidr_set_aff_inst(unsigned long,unsigned char, int);
 extern int psci_change_state(unsigned long, int, int, unsigned int);
 extern int psci_validate_mpidr(unsigned long, int);
diff --git a/common/runtime_svc.c b/common/runtime_svc.c
index 0aa4460..431cfa3 100644
--- a/common/runtime_svc.c
+++ b/common/runtime_svc.c
@@ -38,6 +38,7 @@
 #include <semihosting.h>
 #include <bl_common.h>
 #include <psci.h>
+#include <runtime_svc.h>
 
 /*******************************************************************************
  * Perform initialization of runtime services possibly across exception levels
diff --git a/docs/change-log.md b/docs/change-log.md
index 73d7e7a..8be7a51 100644
--- a/docs/change-log.md
+++ b/docs/change-log.md
@@ -52,6 +52,10 @@ Detailed changes since last release
 *   Definitions of some constants related to the PSCI api calls AFFINITY_INFO
     and CPU_SUSPEND have been corrected.
 
+*   A bug which triggered an error condition in the code executed after a cpu
+    is powered on, if a non zero context id parameter was passed in the PSCI
+    CPU_ON and CPU_SUSPEND api calls has been corrected.
+
 ARM Trusted Firmware - version 0.2
 ==================================
 
diff --git a/docs/porting-guide.md b/docs/porting-guide.md
index 0b07111..c0e6ace 100644
--- a/docs/porting-guide.md
+++ b/docs/porting-guide.md
@@ -188,8 +188,9 @@ the implementer chooses. In the ARM FVP port, they are implemented in
     bytes) of the largest cache line amongst all caches implemented in the
     system. A pointer to this memory should be exported with the name
     `platform_normal_stacks`. This pointer is used by the common platform helper
-    function `platform_set_stack()` to allocate a stack to each CPU in the
-    platform (see [../plat/common/aarch64/platform_helpers.S]).
+    functions `platform_set_stack()` (to allocate a stack for each CPU in the
+    platform)  & `platform_get_stack()` (to return the base address of that
+    stack) (see [../plat/common/aarch64/platform_helpers.S]).
 
 
 2.2 Common optional modifications
@@ -262,6 +263,20 @@ The size of the stack allocated to each CPU is specified by the platform defined
 constant `PLATFORM_STACK_SIZE`.
 
 
+### Function : platform_get_stack()
+
+    Argument : unsigned long
+    Return   : unsigned long
+
+This function uses the `platform_normal_stacks` pointer variable to return the
+base address of the stack memory reserved for a CPU. Further details are given
+in the description of the `platform_normal_stacks` variable below. A CPU is
+identified by its `MPIDR`, which is passed as the argument.
+
+The size of the stack allocated to each CPU is specified by the platform defined
+constant `PLATFORM_STACK_SIZE`.
+
+
 ### Function : plat_report_exception()
 
     Argument : unsigned int
diff --git a/plat/common/aarch64/platform_helpers.S b/plat/common/aarch64/platform_helpers.S
index 8a6f493..770c1e2 100644
--- a/plat/common/aarch64/platform_helpers.S
+++ b/plat/common/aarch64/platform_helpers.S
@@ -35,6 +35,7 @@
 	.globl	pcpu_dv_mem_stack
 	.weak	platform_get_core_pos
 	.weak	platform_set_stack
+	.weak	platform_get_stack
 	.weak	platform_is_primary_cpu
 	.weak	platform_set_coherent_stack
 	.weak	platform_check_mpidr
@@ -95,19 +96,28 @@ platform_is_primary_cpu:; .type platform_is_primary_cpu, %function
 	cset	x0, eq
 	ret
 
-
 	/* -----------------------------------------------------
-	 * void platform_set_stack (int mpidr)
+	 * void platform_get_stack (unsigned long mpidr)
 	 * -----------------------------------------------------
 	 */
-platform_set_stack:; .type platform_set_stack, %function
-	mov	x9, x30 // lr
+platform_get_stack:; .type platform_get_stack, %function
+	mov	x10, x30 // lr
 	bl	platform_get_core_pos
 	add	x0, x0, #1
 	mov	x1, #PLATFORM_STACK_SIZE
 	mul	x0, x0, x1
 	ldr	x1, =platform_normal_stacks
-	add	sp, x1, x0
+	add	x0, x1, x0
+	ret	x10
+
+	/* -----------------------------------------------------
+	 * void platform_set_stack (unsigned long mpidr)
+	 * -----------------------------------------------------
+	 */
+platform_set_stack:; .type platform_set_stack, %function
+	mov	x9, x30 // lr
+	bl	platform_get_stack
+	mov	sp, x0
 	ret	x9
 
 	/* -----------------------------------------------------
diff --git a/plat/fvp/platform.h b/plat/fvp/platform.h
index 399a772..38bd558 100644
--- a/plat/fvp/platform.h
+++ b/plat/fvp/platform.h
@@ -331,6 +331,7 @@ extern unsigned long platform_get_cfgvar(unsigned int);
 extern int platform_config_setup(void);
 extern void plat_report_exception(unsigned long);
 extern unsigned long plat_get_ns_image_entrypoint(void);
+extern unsigned long platform_get_stack(unsigned long mpidr);
 
 /* Declarations for fvp_topology.c */
 extern int plat_setup_topology(void);