[xen master] x86/boot: print CPU and APIC ID in bring up failure

[patchbot@xxxxxxx]

commit f8ffcf1d1043edf3e220d39d406a7c3c66628637
Author:     Roger Pau Monne <roger.pau@xxxxxxxxxx>
AuthorDate: Wed May 21 17:28:47 2025 +0200
Commit:     Roger Pau Monne <roger.pau@xxxxxxxxxx>
CommitDate: Tue May 27 09:11:37 2025 +0200

    x86/boot: print CPU and APIC ID in bring up failure
    
    Print the CPU and APIC ID that fails to respond to the init sequence, or
    that didn't manage to reach the "callin" state.  Expand a bit the printed
    error messages.  Otherwise the "Not responding." message is not easy to
    understand by users.
    
    Reported-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
    Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
 xen/arch/x86/smpboot.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/xen/arch/x86/smpboot.c b/xen/arch/x86/smpboot.c
index 41fe67d43c..adcaec6899 100644
--- a/xen/arch/x86/smpboot.c
+++ b/xen/arch/x86/smpboot.c
@@ -621,10 +621,12 @@ static int do_boot_cpu(int apicid, int cpu)
             smp_mb();
             if ( bootsym(trampoline_cpu_started) == 0xA5 )
                 /* trampoline started but...? */
-                printk("Stuck ??\n");
+                printk("APIC ID %#x (CPU%u) didn't finish start sequence\n",
+                       apicid, cpu);
             else
                 /* trampoline code not run */
-                printk("Not responding.\n");
+                printk("APIC ID %#x (CPU%u) didn't respond to SIPI\n",
+                       apicid, cpu);
         }
     }
 
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