[PATCH v6 17/17] KVM: arm64: Introduce pkvm_dump_backtrace()

[Kalesh Singh <kaleshsingh@google.com>]

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.

[  111.623091] kvm [367]: nVHE call trace:
[  111.623215] kvm [367]:  [<ffff8000090a6570>] __kvm_nvhe_hyp_panic+0xac/0xf8
[  111.623448] kvm [367]:  [<ffff8000090a65cc>] __kvm_nvhe_hyp_panic_bad_stack+0x10/0x10
[  111.623642] kvm [367]:  [<ffff8000090a61e4>] __kvm_nvhe_recursive_death+0x24/0x34
. . .
[  111.640366] kvm [367]:  [<ffff8000090a61e4>] __kvm_nvhe_recursive_death+0x24/0x34
[  111.640467] kvm [367]:  [<ffff8000090a61e4>] __kvm_nvhe_recursive_death+0x24/0x34
[  111.640574] kvm [367]:  [<ffff8000090a5de4>] __kvm_nvhe___kvm_vcpu_run+0x30/0x40c
[  111.640676] kvm [367]:  [<ffff8000090a8b64>] __kvm_nvhe_handle___kvm_vcpu_run+0x30/0x48
[  111.640778] kvm [367]:  [<ffff8000090a88b8>] __kvm_nvhe_handle_trap+0xc4/0x128
[  111.640880] kvm [367]:  [<ffff8000090a7864>] __kvm_nvhe___host_exit+0x64/0x64
[  111.640996] kvm [367]: ---[ end nVHE call trace ]---

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

Changes in v6:
  - And range check when dumping pkvm stacktrace, per Oliver
  - Use consistent nVHE call trace delimiters between protected and
    non-protected mode, per Oliver
  - Fix typo in comment, per Fuad

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

 arch/arm64/kvm/handle_exit.c | 35 ++++++++++++++++++++++++++++++++++-
 1 file changed, 34 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c
index e83e6f735100..c14fc4ba4422 100644
--- a/arch/arm64/kvm/handle_exit.c
+++ b/arch/arm64/kvm/handle_exit.c
@@ -371,6 +371,39 @@ static void hyp_dump_backtrace(unsigned long hyp_offset)
 	kvm_nvhe_dump_backtrace_end();
 }
 
+#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 directly access hypervisor memory in protected
+ * mode.
+ */
+static void pkvm_dump_backtrace(unsigned long hyp_offset)
+{
+	unsigned long *stacktrace
+		= (unsigned long *) this_cpu_ptr_nvhe_sym(pkvm_stacktrace);
+	int i, size = NVHE_STACKTRACE_SIZE / sizeof(long);
+
+	kvm_nvhe_dump_backtrace_start();
+	/* The saved stacktrace is terminated by a null entry */
+	for (i = 0; i < size && stacktrace[i]; i++)
+		kvm_nvhe_dump_backtrace_entry((void *)hyp_offset, stacktrace[i]);
+	kvm_nvhe_dump_backtrace_end();
+}
+#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.
  *
@@ -379,7 +412,7 @@ static void hyp_dump_backtrace(unsigned long hyp_offset)
 static void kvm_nvhe_dump_backtrace(unsigned long hyp_offset)
 {
 	if (is_protected_kvm_enabled())
-		return;
+		pkvm_dump_backtrace(hyp_offset);
 	else
 		hyp_dump_backtrace(hyp_offset);
 }
-- 
2.37.1.359.gd136c6c3e2-goog