The psci test performs a series of CPU_ON/CPU_OFF cycles for CPU 1. This is
done by setting the entry point for the CPU_ON call to the physical address
of the C function cpu_psci_cpu_die.
The compiler is well within its rights to use the stack when generating
code for cpu_psci_cpu_die. However, because no stack initialization has
been done, the stack pointer is zero, as set by KVM when creating the VCPU.
This causes a data abort without a change in exception level. The VBAR_EL1
register is also zero (the KVM reset value for VBAR_EL1), the MMU is off,
and we end up trying to fetch instructions from address 0x200.
At this point, a stage 2 instruction abort is generated which is taken to
KVM. KVM interprets this as an instruction fetch from an I/O region, and
injects a prefetch abort into the guest. Prefetch abort is a synchronous
exception, and on guest return the VCPU PC will be set to VBAR_EL1 + 0x200,
which is... 0x200. The VCPU ends up in an infinite loop causing a prefetch
abort while fetching the instruction to service the said abort.
cpu_psci_cpu_die is basically a wrapper over the HVC instruction, so
provide an assembly implementation for the function which will serve as the
entry point for CPU_ON.
Signed-off-by: Alexandru Elisei <alexandru.elisei@xxxxxxx>
---
arm/cstart.S | 7 +++++++
arm/cstart64.S | 7 +++++++
arm/psci.c | 5 +++--
3 files changed, 17 insertions(+), 2 deletions(-)
diff --git a/arm/cstart.S b/arm/cstart.S
index 2c81d39a666b..dfef48e4dbb2 100644
--- a/arm/cstart.S
+++ b/arm/cstart.S
@@ -7,6 +7,7 @@
*/
#define __ASSEMBLY__
#include <auxinfo.h>
+#include <linux/psci.h>
#include <asm/thread_info.h>
#include <asm/asm-offsets.h>
#include <asm/pgtable-hwdef.h>
@@ -139,6 +140,12 @@ secondary_entry:
blx r0
b do_idle
+.global asm_cpu_psci_cpu_die
+asm_cpu_psci_cpu_die:
+ ldr r0, =PSCI_0_2_FN_CPU_OFF
+ hvc #0
+ b .
+
.globl halt
halt:
1: wfi
diff --git a/arm/cstart64.S b/arm/cstart64.S
index b0e8baa1a23a..c98842f11e90 100644
--- a/arm/cstart64.S
+++ b/arm/cstart64.S
@@ -7,6 +7,7 @@
*/
#define __ASSEMBLY__
#include <auxinfo.h>
+#include <linux/psci.h>
#include <asm/asm-offsets.h>
#include <asm/ptrace.h>
#include <asm/processor.h>
@@ -128,6 +129,12 @@ secondary_entry:
blr x0
b do_idle
+.globl asm_cpu_psci_cpu_die
+asm_cpu_psci_cpu_die:
+ ldr x0, =PSCI_0_2_FN_CPU_OFF
+ hvc #0
+ b .
+
.globl halt
halt:
1: wfi
diff --git a/arm/psci.c b/arm/psci.c
index 5c1accb6cea4..c45a39c7d6e8 100644
--- a/arm/psci.c
+++ b/arm/psci.c
@@ -72,6 +72,7 @@ static int cpu_on_ret[NR_CPUS];
static cpumask_t cpu_on_ready, cpu_on_done;
static volatile int cpu_on_start;
+extern void asm_cpu_psci_cpu_die(void);
static void cpu_on_secondary_entry(void)
{
int cpu = smp_processor_id();
@@ -79,7 +80,7 @@ static void cpu_on_secondary_entry(void)
cpumask_set_cpu(cpu, &cpu_on_ready);
while (!cpu_on_start)
cpu_relax();
- cpu_on_ret[cpu] = psci_cpu_on(cpus[1], __pa(cpu_psci_cpu_die));
+ cpu_on_ret[cpu] = psci_cpu_on(cpus[1], __pa(asm_cpu_psci_cpu_die));
cpumask_set_cpu(cpu, &cpu_on_done);
}
@@ -104,7 +105,7 @@ static bool psci_cpu_on_test(void)
cpu_on_start = 1;
smp_mb();
- cpu_on_ret[0] = psci_cpu_on(cpus[1], __pa(cpu_psci_cpu_die));
+ cpu_on_ret[0] = psci_cpu_on(cpus[1], __pa(asm_cpu_psci_cpu_die));
cpumask_set_cpu(0, &cpu_on_done);
while (!cpumask_full(&cpu_on_done))
--
2.7.4
