[PATCH v5 16/17] KVM: arm64: Introduce pkvm_dump_backtrace()

[Kalesh Singh]

Dumps the pKVM hypervisor backtrace from EL1 by reading the unwinded
addresses from the shared stacktrace buffer.

The nVHE hyp backtrace is dumped on hyp_panic(), before panicking the
host.

Signed-off-by: Kalesh Singh <kaleshsingh at google.com>
---

Changes in v5:
  - Move code out from nvhe.h header to handle_exit.c, per Marc
  - Fix stacktrace symoblization when CONFIG_RAMDOMIZE_BASE is enabled,
    per Fuad
  - Use regular comments instead of doc comments, per Fuad

 arch/arm64/kvm/handle_exit.c | 54 ++++++++++++++++++++++++++++++++++++
 1 file changed, 54 insertions(+)

diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c
index f66c0142b335..ad568da5c7d7 100644
--- a/arch/arm64/kvm/handle_exit.c
+++ b/arch/arm64/kvm/handle_exit.c
@@ -318,6 +318,57 @@ void handle_exit_early(struct kvm_vcpu *vcpu, int exception_index)
 		kvm_handle_guest_serror(vcpu, kvm_vcpu_get_esr(vcpu));
 }
 
+#ifdef CONFIG_PROTECTED_NVHE_STACKTRACE
+DECLARE_KVM_NVHE_PER_CPU(unsigned long [NVHE_STACKTRACE_SIZE/sizeof(long)],
+			 pkvm_stacktrace);
+
+/*
+ * pkvm_dump_backtrace - Dump the protected nVHE HYP backtrace.
+ *
+ * @hyp_offset: hypervisor offset, used for address translation.
+ *
+ * Dumping of the pKVM HYP backtrace is done by reading the
+ * stack addresses from the shared stacktrace buffer, since the
+ * host cannot direclty access hyperviosr memory in protected
+ * mode.
+ */
+static void pkvm_dump_backtrace(unsigned long hyp_offset)
+{
+	unsigned long *stacktrace_entry
+		= (unsigned long *)this_cpu_ptr_nvhe_sym(pkvm_stacktrace);
+	unsigned long va_mask, pc;
+
+	va_mask = GENMASK_ULL(vabits_actual - 1, 0);
+
+	kvm_err("Protected nVHE HYP call trace:\n");
+
+	/* The stack trace is terminated by a null entry */
+	for (; *stacktrace_entry; stacktrace_entry++) {
+		/* Mask tags and convert to kern addr */
+		pc = (*stacktrace_entry & va_mask) + hyp_offset;
+		kvm_err(" [<%016lx>] %pB\n", pc, (void *)(pc + kaslr_offset()));
+	}
+
+	kvm_err("---- End of Protected nVHE HYP call trace ----\n");
+}
+#else	/* !CONFIG_PROTECTED_NVHE_STACKTRACE */
+static void pkvm_dump_backtrace(unsigned long hyp_offset)
+{
+	kvm_err("Cannot dump pKVM nVHE stacktrace: !CONFIG_PROTECTED_NVHE_STACKTRACE\n");
+}
+#endif /* CONFIG_PROTECTED_NVHE_STACKTRACE */
+
+/*
+ * kvm_nvhe_dump_backtrace - Dump KVM nVHE hypervisor backtrace.
+ *
+ * @hyp_offset: hypervisor offset, used for address translation.
+ */
+static void kvm_nvhe_dump_backtrace(unsigned long hyp_offset)
+{
+	if (is_protected_kvm_enabled())
+		pkvm_dump_backtrace(hyp_offset);
+}
+
 void __noreturn __cold nvhe_hyp_panic_handler(u64 esr, u64 spsr,
 					      u64 elr_virt, u64 elr_phys,
 					      u64 par, uintptr_t vcpu,
@@ -353,6 +404,9 @@ void __noreturn __cold nvhe_hyp_panic_handler(u64 esr, u64 spsr,
 				(void *)panic_addr);
 	}
 
+	/* Dump the nVHE hypervisor backtrace */
+	kvm_nvhe_dump_backtrace(hyp_offset);
+
 	/*
 	 * Hyp has panicked and we're going to handle that by panicking the
 	 * kernel. The kernel offset will be revealed in the panic so we're
-- 
2.37.0.170.g444d1eabd0-goog