xen/riscv: dump GPRs and CSRs on unexpected traps

Provide additional context when an unexpected exception occurs by dumping
the relevant Supervisor, Virtual Supervisor (VS), and Hypervisor CSRs,
along with the general-purpose registers associated with the trap.

Dumping VS-mode CSRs in addition to host CSRs is beneficial when analysing
VS-mode traps. VSCAUSE, VSEPC, VSTVAL, and related VS state are required to
properly diagnose unexpected guest traps and potential hypervisor
misconfiguration.
For example, on an illegal-instruction exception the hardware may record
the faulting instruction in VSTVAL. If VSTVAL is zero, VSEPC should always
be inspected, and can be used together with objdump to identify the
faulting instruction. Dumping VSCAUSE is also useful when the guest does
not report it, or when the hypervisor redirects a trap to the guest using
VSCAUSE, VSTATUS, and VSTVEC, allowing verification that a subsequent trap
is not caused by incorrect VS state.

Signed-off-by: Oleksii Kurochko <oleksii.kurochko@gmail.com>
Acked-by: Jan Beulich <jbeulich@suse.com>

xen/arch/riscv/traps.c

@@ -99,11 +99,66 @@ static const char *decode_cause(unsigned long cause)
     return decode_trap_cause(cause);
 }
 
+static void dump_general_regs(const struct cpu_user_regs *regs)
+{
+#define X(regs, name, delim) \
+    printk("%-4s: %016lx" delim, #name, (regs)->name)
+
+    X(regs, ra, " "); X(regs, sp, "\n");
+    X(regs, gp, " "); X(regs, tp, "\n");
+    X(regs, t0, " "); X(regs, t1, "\n");
+    X(regs, t2, " "); X(regs, s0, "\n");
+    X(regs, s1, " "); X(regs, a0, "\n");
+    X(regs, a1, " "); X(regs, a2, "\n");
+    X(regs, a3, " "); X(regs, a4, "\n");
+    X(regs, a5, " "); X(regs, a6, "\n");
+    X(regs, a7, " "); X(regs, s2, "\n");
+    X(regs, s3, " "); X(regs, s4, "\n");
+    X(regs, s5, " "); X(regs, s6, "\n");
+    X(regs, s7, " "); X(regs, s8, "\n");
+    X(regs, s9, " "); X(regs, s10, "\n");
+    X(regs, s11, " "); X(regs, t3, "\n");
+    X(regs, t4, " "); X(regs, t5, "\n");
+    X(regs, t6, "\n");
+
+#undef X
+}
+
+static void dump_csrs(const char *ctx)
+{
+    unsigned long v;
+
+#define X(name, csr, fmt, ...) \
+    v = csr_read(csr); \
+    printk("%-10s: %016lx" fmt, #name, v, ##__VA_ARGS__)
+
+    X(scause, CSR_SCAUSE, " %s[%s]\n", ctx, decode_cause(v));
+
+    X(htval, CSR_HTVAL, " ");  X(htinst, CSR_HTINST, "\n");
+    X(hedeleg, CSR_HEDELEG, " "); X(hideleg, CSR_HIDELEG, "\n");
+    X(hstatus, CSR_HSTATUS, " [%s%s%s%s%s%s ]\n",
+      (v & HSTATUS_VTSR) ? " VTSR" : "",
+      (v & HSTATUS_VTVM) ? " VTVM" : "",
+      (v & HSTATUS_HU)   ? " HU"   : "",
+      (v & HSTATUS_SPVP) ? " SPVP" : "",
+      (v & HSTATUS_SPV)  ? " SPV"  : "",
+      (v & HSTATUS_GVA)  ? " GVA"  : "");
+    X(hgatp, CSR_HGATP, "\n");
+    X(hstateen0, CSR_HSTATEEN0, "\n");
+    X(stvec, CSR_STVEC, " "); X(vstvec, CSR_VSTVEC, "\n");
+    X(sepc, CSR_SEPC, " "); X(vsepc, CSR_VSEPC, "\n");
+    X(stval, CSR_STVAL, " "); X(vstval, CSR_VSTVAL, "\n");
+    X(status, CSR_SSTATUS, " "); X(vsstatus, CSR_VSSTATUS, "\n");
+    X(satp, CSR_SATP, "\n");
+    X(vscause, CSR_VSCAUSE, " [%s]\n", decode_cause(v));
+
+#undef X
+}
+
 static void do_unexpected_trap(const struct cpu_user_regs *regs)
 {
-    unsigned long cause = csr_read(CSR_SCAUSE);
+    dump_csrs("Unhandled exception");
-
+    dump_general_regs(regs);
-    printk("Unhandled exception: %s\n", decode_cause(cause));
 
     die();
 }