KVM: arm64: Move nVHE stacktrace unwinding into its own compilation unit

The unwinding code doesn't really belong to the exit handling
code. Instead, move it to a file (conveniently named stacktrace.c
to confuse the reviewer), and move all the stacktrace-related
stuff there.

It will be joined by more code very soon.

Signed-off-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: Kalesh Singh <kaleshsingh@google.com>
Tested-by: Kalesh Singh <kaleshsingh@google.com>
Reviewed-by: Oliver Upton <oliver.upton@linux.dev>
Link: https://lore.kernel.org/r/20220727142906.1856759-3-maz@kernel.org

1 files changed, 120 insertions, 0 deletions

diff --git a/arch/arm64/kvm/stacktrace.c b/arch/arm64/kvm/stacktrace.c
new file mode 100644
index 000000000000..9812aefdcfb4
--- /dev/null
+++ b/arch/arm64/kvm/stacktrace.c
@@ -0,0 +1,120 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * KVM nVHE hypervisor stack tracing support.
+ *
+ * The unwinder implementation depends on the nVHE mode:
+ *
+ *   1) Non-protected nVHE mode - the host can directly access the
+ *      HYP stack pages and unwind the HYP stack in EL1. This saves having
+ *      to allocate shared buffers for the host to read the unwinded
+ *      stacktrace.
+ *
+ *   2) pKVM (protected nVHE) mode - the host cannot directly access
+ *      the HYP memory. The stack is unwinded in EL2 and dumped to a shared
+ *      buffer where the host can read and print the stacktrace.
+ *
+ * Copyright (C) 2022 Google LLC
+ */
+
+#include <linux/kvm.h>
+#include <linux/kvm_host.h>
+
+#include <asm/stacktrace/nvhe.h>
+
+/*
+ * kvm_nvhe_dump_backtrace_entry - Symbolize and print an nVHE backtrace entry
+ *
+ * @arg    : the hypervisor offset, used for address translation
+ * @where  : the program counter corresponding to the stack frame
+ */
+static bool kvm_nvhe_dump_backtrace_entry(void *arg, unsigned long where)
+{
+	unsigned long va_mask = GENMASK_ULL(vabits_actual - 1, 0);
+	unsigned long hyp_offset = (unsigned long)arg;
+
+	/* Mask tags and convert to kern addr */
+	where = (where & va_mask) + hyp_offset;
+	kvm_err(" [<%016lx>] %pB\n", where, (void *)(where + kaslr_offset()));
+
+	return true;
+}
+
+static void kvm_nvhe_dump_backtrace_start(void)
+{
+	kvm_err("nVHE call trace:\n");
+}
+
+static void kvm_nvhe_dump_backtrace_end(void)
+{
+	kvm_err("---[ end nVHE call trace ]---\n");
+}
+
+/*
+ * hyp_dump_backtrace - Dump the non-protected nVHE backtrace.
+ *
+ * @hyp_offset: hypervisor offset, used for address translation.
+ *
+ * The host can directly access HYP stack pages in non-protected
+ * mode, so the unwinding is done directly from EL1. This removes
+ * the need for shared buffers between host and hypervisor for
+ * the stacktrace.
+ */
+static void hyp_dump_backtrace(unsigned long hyp_offset)
+{
+	struct kvm_nvhe_stacktrace_info *stacktrace_info;
+	struct unwind_state state;
+
+	stacktrace_info = this_cpu_ptr_nvhe_sym(kvm_stacktrace_info);
+
+	kvm_nvhe_unwind_init(&state, stacktrace_info->fp, stacktrace_info->pc);
+
+	kvm_nvhe_dump_backtrace_start();
+	unwind(&state, kvm_nvhe_dump_backtrace_entry, (void *)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.
+ *
+ * @hyp_offset: hypervisor offset, used for address translation.
+ */
+void kvm_nvhe_dump_backtrace(unsigned long hyp_offset)
+{
+	if (is_protected_kvm_enabled())
+		pkvm_dump_backtrace(hyp_offset);
+	else
+		hyp_dump_backtrace(hyp_offset);
+}