[PATCH v4 17/18] KVM: arm64: Introduce hyp_dump_backtrace()

[Kalesh Singh]

In non-protected nVHE mode, unwinds and dumps the hypervisor backtrace
from EL1. This is possible beacuase the host can directly access the
hypervisor stack pages in non-proteced mode.

Signed-off-by: Kalesh Singh <kaleshsingh@xxxxxxxxxx>
---
 arch/arm64/include/asm/stacktrace/nvhe.h | 64 +++++++++++++++++++++---
 1 file changed, 56 insertions(+), 8 deletions(-)

diff --git a/arch/arm64/include/asm/stacktrace/nvhe.h b/arch/arm64/include/asm/stacktrace/nvhe.h
index ec1a4ee21c21..c322ac95b256 100644
--- a/arch/arm64/include/asm/stacktrace/nvhe.h
+++ b/arch/arm64/include/asm/stacktrace/nvhe.h
@@ -190,6 +190,56 @@ static int notrace unwind_next(struct unwind_state *state)
 }
 NOKPROBE_SYMBOL(unwind_next);
 
+/**
+ * kvm_nvhe_print_backtrace_entry - Symbolizes and prints the HYP stack address
+ */
+static inline void kvm_nvhe_print_backtrace_entry(unsigned long addr,
+						  unsigned long hyp_offset)
+{
+	unsigned long va_mask = GENMASK_ULL(vabits_actual - 1, 0);
+
+	/* Mask tags and convert to kern addr */
+	addr = (addr & va_mask) + hyp_offset;
+	kvm_err(" [<%016lx>] %pB\n", addr, (void *)addr);
+}
+
+/**
+ * hyp_backtrace_entry - Dump an entry of the non-protected nVHE HYP stacktrace
+ *
+ * @arg    : the hypervisor offset, used for address translation
+ * @where  : the program counter corresponding to the stack frame
+ */
+static inline bool hyp_dump_backtrace_entry(void *arg, unsigned long where)
+{
+	kvm_nvhe_print_backtrace_entry(where, (unsigned long)arg);
+
+	return true;
+}
+
+/**
+ * hyp_dump_backtrace - Dump the non-proteced nVHE HYP 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 inline 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_err("Non-protected nVHE HYP call trace:\n");
+	unwind(&state, hyp_dump_backtrace_entry, (void *)hyp_offset);
+	kvm_err("---- End of Non-protected nVHE HYP call trace ----\n");
+}
+
 #ifdef CONFIG_PROTECTED_NVHE_STACKTRACE
 DECLARE_KVM_NVHE_PER_CPU(unsigned long [NVHE_STACKTRACE_SIZE/sizeof(long)], pkvm_stacktrace);
 
@@ -206,22 +256,18 @@ DECLARE_KVM_NVHE_PER_CPU(unsigned long [NVHE_STACKTRACE_SIZE/sizeof(long)], pkvm
 static inline void pkvm_dump_backtrace(unsigned long hyp_offset)
 {
 	unsigned long *stacktrace_pos;
-	unsigned long va_mask, pc;
 
 	stacktrace_pos = (unsigned long *)this_cpu_ptr_nvhe_sym(pkvm_stacktrace);
-	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_pos; stacktrace_pos++) {
-		/* Mask tags and convert to kern addr */
-		pc = (*stacktrace_pos & va_mask) + hyp_offset;
-		kvm_err(" [<%016lx>] %pB\n", pc, (void *)pc);
-	}
+	/* The saved stacktrace is terminated by a null entry */
+	for (; *stacktrace_pos; stacktrace_pos++)
+		kvm_nvhe_print_backtrace_entry(*stacktrace_pos, hyp_offset);
 
 	kvm_err("---- End of Protected nVHE HYP call trace ----\n");
 }
+
 #else	/* !CONFIG_PROTECTED_NVHE_STACKTRACE */
 static inline void pkvm_dump_backtrace(unsigned long hyp_offset)
 {
@@ -238,6 +284,8 @@ static inline 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);
 }
 #endif	/* __KVM_NVHE_HYPERVISOR__ */
 #endif	/* __ASM_STACKTRACE_NVHE_H */
-- 
2.37.0.170.g444d1eabd0-goog