[xen staging] xen/riscv: dump GPRs and CSRs on unexpected traps

[patchbot@xxxxxxx]

commit 3babc8d2e54614334e353096e1fdd14bb83516a9
Author:     Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
AuthorDate: Thu Jan 29 09:53:10 2026 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Thu Jan 29 09:53:10 2026 +0100

    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@xxxxxxxxx>
    Acked-by: Jan Beulich <jbeulich@xxxxxxxx>
---
 xen/arch/riscv/traps.c | 61 +++++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 58 insertions(+), 3 deletions(-)

diff --git a/xen/arch/riscv/traps.c b/xen/arch/riscv/traps.c
index e9c9677863..84b5ab4142 100644
--- a/xen/arch/riscv/traps.c
+++ b/xen/arch/riscv/traps.c
@@ -99,11 +99,66 @@ static const char *decode_cause(unsigned long cause)
     return decode_trap_cause(cause);
 }
 
-static void do_unexpected_trap(const struct cpu_user_regs *regs)
+static void dump_general_regs(const struct cpu_user_regs *regs)
 {
-    unsigned long cause = csr_read(CSR_SCAUSE);
+#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
+}
 
-    printk("Unhandled exception: %s\n", decode_cause(cause));
+static void do_unexpected_trap(const struct cpu_user_regs *regs)
+{
+    dump_csrs("Unhandled exception");
+    dump_general_regs(regs);
 
     die();
 }
--
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