Re: [PATCH v5 17/17] KVM: arm64: Introduce hyp_dump_backtrace()

Signed-off-by: Kalesh Singh <redacted>
---

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 | 65 +++++++++++++++++++++++++++++++-----
 1 file changed, 56 insertions(+), 9 deletions(-)

diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c
index ad568da5c7d7..432b6b26f4ad 100644
--- a/arch/arm64/kvm/handle_exit.c
+++ b/arch/arm64/kvm/handle_exit.c

@@ -17,6 +17,7 @@
 #include <asm/kvm_emulate.h>
 #include <asm/kvm_mmu.h>
 #include <asm/debug-monitors.h>
+#include <asm/stacktrace/nvhe.h>
 #include <asm/traps.h>

 #include <kvm/arm_hypercalls.h>

@@ -318,6 +319,56 @@ void handle_exit_early(struct kvm_vcpu *vcpu, int exception_index)
                kvm_handle_guest_serror(vcpu, kvm_vcpu_get_esr(vcpu));
 }

+/*
+ * kvm_nvhe_print_backtrace_entry - Symbolizes and prints the HYP stack address
+ */
+static 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 + kaslr_offset()));
+}
+
+/*
+ * hyp_dump_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 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 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);

@@ -336,18 +387,12 @@ 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()));
-       }
+       /* The saved stacktrace is terminated by a null entry */
+       for (; *stacktrace_entry; stacktrace_entry++)
+               kvm_nvhe_print_backtrace_entry(*stacktrace_entry, hyp_offset);

        kvm_err("---- End of Protected nVHE HYP call trace ----\n");
 }

@@ -367,6 +412,8 @@ static 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);
 }

 void __noreturn __cold nvhe_hyp_panic_handler(u64 esr, u64 spsr,
--

2.37.0.170.g444d1eabd0-goog