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Re: [PATCH 1/1] hw/core/cpu: always print cpu index with cpu state


From: Philippe Mathieu-Daudé
Subject: Re: [PATCH 1/1] hw/core/cpu: always print cpu index with cpu state
Date: Tue, 7 Feb 2023 18:49:51 +0100
User-agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:102.0) Gecko/20100101 Thunderbird/102.6.1

On 7/2/23 18:32, Dongli Zhang wrote:
Hi Philippe,

On 2/6/23 23:16, Philippe Mathieu-Daudé wrote:
On 7/2/23 00:42, Dongli Zhang wrote:
The cpu_dump_state() does not print the cpu index. When the
cpu_dump_state() is invoked due to the KVM failure, we are not able to tell
from which CPU the state is. The below is an example.

KVM internal error. Suberror: 764064
RAX=0000000000000002 RBX=ffff8a9e57c38400 RCX=00000000ffffffff
RDX=ffff8a9cc00ba8a0
RSI=0000000000000003 RDI=ffff8a9e57c38400 RBP=ffffb6120c5b3c50
RSP=ffffb6120c5b3c40
R8 =0000000000000000 R9 =ffff8a9cc00ba8a0 R10=ffffffff8e467350
R11=0000000000000007
R12=000000000000000a R13=ffffffff8f987e25 R14=ffffffff8f988a01
R15=0000000000000000
RIP=ffffffff8e51bb04 RFL=00010046 [---Z-P-] CPL=0 II=0 A20=1 SMM=0 HLT=0
ES =0000 0000000000000000 ffffffff 00c00000
CS =0010 0000000000000000 ffffffff 00a09b00 DPL=0 CS64 [-RA]
SS =0000 0000000000000000 ffffffff 00c00000
DS =0000 0000000000000000 ffffffff 00c00000
FS =0000 0000000000000000 ffffffff 00c00000
GS =0000 ffff8ac27fcc0000 ffffffff 00c00000
LDT=0000 0000000000000000 ffffffff 00c00000
TR =0040 fffffe0000096000 0000206f 00008b00 DPL=0 TSS64-busy
GDT=     fffffe0000094000 0000007f
IDT=     fffffe0000000000 00000fff
CR0=80050033 CR2=0000000000000000 CR3=00000010ca40a001 CR4=003606e0
DR0=0000000000000000 DR1=0000000000000000 DR2=0000000000000000
DR3=0000000000000000
DR6=00000000fffe0ff0 DR7=0000000000000400
EFER=0000000000000d01
Code=0f 1f ... ...

Print the cpu->cpu_index in cpu_dump_state() and remove it from the caller.

Cc: Joe Jin <joe.jin@oracle.com>
Signed-off-by: Dongli Zhang <dongli.zhang@oracle.com>
---
   hw/core/cpu-common.c      | 1 +
   monitor/hmp-cmds-target.c | 2 --
   softmmu/cpus.c            | 1 -
   3 files changed, 1 insertion(+), 3 deletions(-)

diff --git a/hw/core/cpu-common.c b/hw/core/cpu-common.c
index 5ccc3837b6..d2503f2d09 100644
--- a/hw/core/cpu-common.c
+++ b/hw/core/cpu-common.c
@@ -105,6 +105,7 @@ void cpu_dump_state(CPUState *cpu, FILE *f, int flags)
         if (cc->dump_state) {
           cpu_synchronize_state(cpu);

Should we check for:

           if (cpu->cpu_index != -1) {

+        qemu_fprintf(f, "\nCPU#%d\n", cpu->cpu_index);

           }

I think you meant if (cpu->cpu_index != UNASSIGNED_CPU_INDEX).

I do not see this case may happen within my knowledge. The cpu_index is always
expected to be assigned if cpu_exec_realizefn()-->cpu_list_add() is called.

  83 void cpu_list_add(CPUState *cpu)
  84 {
  85     QEMU_LOCK_GUARD(&qemu_cpu_list_lock);
  86     if (cpu->cpu_index == UNASSIGNED_CPU_INDEX) {
  87         cpu->cpu_index = cpu_get_free_index();
  88         assert(cpu->cpu_index != UNASSIGNED_CPU_INDEX);
  89     } else {
  90         assert(!cpu_index_auto_assigned);
  91     }
  92     QTAILQ_INSERT_TAIL_RCU(&cpus, cpu, node);
  93     cpu_list_generation_id++;
  94 }


In addition, the cc->dump_state() is always invoked by cpu_dump_state(). As a
result, e.g., arm_cpu_dump_state() or x86_cpu_dump_state() may always print the
cpu state unconditionally (same for mips, s390 or riscv). I do not see a reason
to hide the cpu_index.

Would you please let me know if the above is wrong? I do not think it is
required to filter the cpu_index with UNASSIGNED_CPU_INDEX.

You are right.

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>

Thanks for clarifying!



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