KVM: arm64: Implement protected nVHE hyp stack unwinder

Implements the common framework necessary for unwind() to work in
the protected nVHE context:
   - on_accessible_stack()
   - on_overflow_stack()
   - unwind_next()

Protected nVHE unwind() is used to unwind and save the hyp stack
addresses to the shared stacktrace buffer. The host reads the
entries in this buffer, symbolizes and dumps the stacktrace (later
patch in the series).
Signed-off-by: Kalesh Singh <kaleshsingh@google.com>
Reviewed-by: Fuad Tabba <tabba@google.com>
Tested-by: Fuad Tabba <tabba@google.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20220726073750.3219117-17-kaleshsingh@google.com

arch/arm64/include/asm/stacktrace/nvhe.h

@@ -64,18 +64,27 @@ static inline bool on_accessible_stack(const struct task_struct *tsk,
 static inline bool on_overflow_stack(unsigned long sp, unsigned long size,
 				     struct stack_info *info)
 {
-	return false;
+	unsigned long low = (unsigned long)this_cpu_ptr(overflow_stack);
+	unsigned long high = low + OVERFLOW_STACK_SIZE;
+
+	return on_stack(sp, size, low, high, STACK_TYPE_OVERFLOW, info);
 }
 
 static inline bool on_hyp_stack(unsigned long sp, unsigned long size,
 				struct stack_info *info)
 {
-	return false;
+	struct kvm_nvhe_init_params *params = this_cpu_ptr(&kvm_init_params);
+	unsigned long high = params->stack_hyp_va;
+	unsigned long low = high - PAGE_SIZE;
+
+	return on_stack(sp, size, low, high, STACK_TYPE_HYP, info);
 }
 
 static inline int notrace unwind_next(struct unwind_state *state)
 {
-	return 0;
+	struct stack_info info;
+
+	return unwind_next_common(state, &info, NULL);
 }
 NOKPROBE_SYMBOL(unwind_next);
 #endif	/* CONFIG_PROTECTED_NVHE_STACKTRACE */