arm64: smp: disable hotplug on trusted OS resident CPU

The trusted OS may reject CPU_OFF calls to its resident CPU, so we must
avoid issuing those. We never migrate a Trusted OS and we already take
care to prevent CPU_OFF PSCI call. However, this is not reflected
explicitly to the userspace. Any user can attempt to hotplug trusted OS
resident CPU. The entire motion of going through the various state
transitions in the CPU hotplug state machine gets executed and the
PSCI layer finally refuses to make CPU_OFF call.

This results is unnecessary unwinding of CPU hotplug state machine in
the kernel. Instead we can mark the trusted OS resident CPU as not
available for hotplug, so that the user attempt or request to do the
same will get immediately rejected.

Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>

1 files changed, 3 insertions, 0 deletions

diff --git a/arch/arm64/include/asm/cpu_ops.h b/arch/arm64/include/asm/cpu_ops.h
index c09d633c3109..86aabf1e0199 100644
--- a/arch/arm64/include/asm/cpu_ops.h
+++ b/arch/arm64/include/asm/cpu_ops.h
@@ -23,6 +23,8 @@
  * @cpu_boot:	Boots a cpu into the kernel.
  * @cpu_postboot: Optionally, perform any post-boot cleanup or necesary
  *		synchronisation. Called from the cpu being booted.
+ * @cpu_can_disable: Determines whether a CPU can be disabled based on
+ *		mechanism-specific information.
  * @cpu_disable: Prepares a cpu to die. May fail for some mechanism-specific
  * 		reason, which will cause the hot unplug to be aborted. Called
  * 		from the cpu to be killed.
@@ -42,6 +44,7 @@ struct cpu_operations {
 	int		(*cpu_boot)(unsigned int);
 	void		(*cpu_postboot)(void);
 #ifdef CONFIG_HOTPLUG_CPU
+	bool		(*cpu_can_disable)(unsigned int cpu);
 	int		(*cpu_disable)(unsigned int cpu);
 	void		(*cpu_die)(unsigned int cpu);
 	int		(*cpu_kill)(unsigned int cpu);