KVM: arm64: Implement non-protected nVHE hyp stack unwinder

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

Non-protected nVHE unwind() is used to unwind and dump the hypervisor
stacktrace by the host in EL1

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/20220726073750.3219117-11-kaleshsingh@google.com

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

@@ -34,6 +34,7 @@ enum stack_type {
 	STACK_TYPE_OVERFLOW,
 	STACK_TYPE_SDEI_NORMAL,
 	STACK_TYPE_SDEI_CRITICAL,
+	STACK_TYPE_HYP,
 	__NR_STACK_TYPES
 };
 
@@ -186,6 +187,7 @@ static inline int unwind_next_common(struct unwind_state *state,
 	 *
 	 * TASK -> IRQ -> OVERFLOW -> SDEI_NORMAL
 	 * TASK -> SDEI_NORMAL -> SDEI_CRITICAL -> OVERFLOW
+	 * HYP -> OVERFLOW
 	 *
 	 * ... but the nesting itself is strict. Once we transition from one
 	 * stack to another, it's never valid to unwind back to that first

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

@@ -16,10 +16,19 @@
 
 #include <asm/stacktrace/common.h>
 
+static inline bool on_hyp_stack(unsigned long sp, unsigned long size,
+				struct stack_info *info);
+
 static inline bool on_accessible_stack(const struct task_struct *tsk,
 				       unsigned long sp, unsigned long size,
 				       struct stack_info *info)
 {
+	if (on_accessible_stack_common(tsk, sp, size, info))
+		return true;
+
+	if (on_hyp_stack(sp, size, info))
+		return true;
+
 	return false;
 }
 
@@ -31,15 +40,78 @@ static inline bool on_accessible_stack(const struct task_struct *tsk,
  * (by the host in EL1).
  */
 
+DECLARE_KVM_NVHE_PER_CPU(unsigned long [OVERFLOW_STACK_SIZE/sizeof(long)], overflow_stack);
+DECLARE_KVM_NVHE_PER_CPU(struct kvm_nvhe_stacktrace_info, kvm_stacktrace_info);
+DECLARE_PER_CPU(unsigned long, kvm_arm_hyp_stack_page);
+
+/*
+ * kvm_nvhe_stack_kern_va - Convert KVM nVHE HYP stack addresses to a kernel VAs
+ *
+ * The nVHE hypervisor stack is mapped in the flexible 'private' VA range, to
+ * allow for guard pages below the stack. Consequently, the fixed offset address
+ * translation macros won't work here.
+ *
+ * The kernel VA is calculated as an offset from the kernel VA of the hypervisor
+ * stack base.
+ *
+ * Returns true on success and updates @addr to its corresponding kernel VA;
+ * otherwise returns false.
+ */
+static inline bool kvm_nvhe_stack_kern_va(unsigned long *addr,
+					  enum stack_type type)
+{
+	struct kvm_nvhe_stacktrace_info *stacktrace_info;
+	unsigned long hyp_base, kern_base, hyp_offset;
+
+	stacktrace_info = this_cpu_ptr_nvhe_sym(kvm_stacktrace_info);
+
+	switch (type) {
+	case STACK_TYPE_HYP:
+		kern_base = (unsigned long)*this_cpu_ptr(&kvm_arm_hyp_stack_page);
+		hyp_base = (unsigned long)stacktrace_info->stack_base;
+		break;
+	case STACK_TYPE_OVERFLOW:
+		kern_base = (unsigned long)this_cpu_ptr_nvhe_sym(overflow_stack);
+		hyp_base = (unsigned long)stacktrace_info->overflow_stack_base;
+		break;
+	default:
+		return false;
+	}
+
+	hyp_offset = *addr - hyp_base;
+
+	*addr = kern_base + hyp_offset;
+
+	return true;
+}
+
 static inline bool on_overflow_stack(unsigned long sp, unsigned long size,
 				     struct stack_info *info)
 {
-	return false;
+	struct kvm_nvhe_stacktrace_info *stacktrace_info
+				= this_cpu_ptr_nvhe_sym(kvm_stacktrace_info);
+	unsigned long low = (unsigned long)stacktrace_info->overflow_stack_base;
+	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)
+{
+	struct kvm_nvhe_stacktrace_info *stacktrace_info
+				= this_cpu_ptr_nvhe_sym(kvm_stacktrace_info);
+	unsigned long low = (unsigned long)stacktrace_info->stack_base;
+	unsigned long high = low + 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, kvm_nvhe_stack_kern_va);
 }
 NOKPROBE_SYMBOL(unwind_next);
 

arch/arm64/kvm/arm.c

@@ -49,7 +49,7 @@ DEFINE_STATIC_KEY_FALSE(kvm_protected_mode_initialized);
 
 DECLARE_KVM_HYP_PER_CPU(unsigned long, kvm_hyp_vector);
 
-static DEFINE_PER_CPU(unsigned long, kvm_arm_hyp_stack_page);
+DEFINE_PER_CPU(unsigned long, kvm_arm_hyp_stack_page);
 unsigned long kvm_arm_hyp_percpu_base[NR_CPUS];
 DECLARE_KVM_NVHE_PER_CPU(struct kvm_nvhe_init_params, kvm_init_params);