[Crash-utility] [PATCH] Fix pvops Xen detection for arm machine

[Qi Zheng]

On 2021/12/20 4:29 PM, lijiang wrote:
> Hi, Qi
> Thank you for the fix.
> 
>> Date: Thu, 16 Dec 2021 15:09:49 +0800
>> From: Qi Zheng <zhengqi.arch at bytedance.com>
>> To: k-hagio-ab at nec.com, ptesarik at suse.com, lijiang at redhat.com
>> Cc: Qi Zheng <zhengqi.arch at bytedance.com>, crash-utility at redhat.com
>> Subject: [Crash-utility] [PATCH] Fix pvops Xen detection for arm
>>          machine
>> Message-ID: <20211216070949.17668-1-zhengqi.arch at bytedance.com>
>> Content-Type: text/plain; charset="US-ASCII"
>>
>> Since the xen_start_info on the arm/arm64 platform is static defined:
>>
>> ./arm/xen/enlighten.c:40:static struct start_info _xen_start_info;
>> ./arm/xen/enlighten.c:41:struct start_info *xen_start_info = &_xen_start_info;
>> ./arm/xen/enlighten.c:42:EXPORT_SYMBOL(xen_start_info);
>>
> The above variable is statically defined in the kernel, but the
> 'xen_vcpu_info' is also a static variable, why does the former not
> work on arm machines, but the latter works well? Could you please
> explain more details?
> [linux]$ grep -nr "xen_vcpu_info" *
> arch/arm/xen/enlighten.c:51:static struct vcpu_info __percpu *xen_vcpu_info;

Hi Lianbo,

The 'xen_vcpu_info' is also a static variable on the arm/arm64 platform,
but different from 'xen_start_info', it is assigned during the
initialization process.

Thanks,
Qi

> 
> Thanks.
> Lianbo
> 
>> The is_pvops_xen() in commit 4badc6229c69f5cd9da7eb7bdf400a53ec6db01a
>> ("Fix pvops Xen detection for kernels >= v4.20") always return TRUE.
>> Then the following error will be reported because p2m_mid_missing
>> and xen_p2m_addr are not defined:
>>
>>          crash: cannot resolve "p2m_top"
>>
>> For the arm/arm64 platform, fix it by using xen_vcpu_info instead of
>> xen_start_info to detect Xen dumps.
>>
>> Signed-off-by: Qi Zheng <zhengqi.arch at bytedance.com>
>> ---
>>   kernel.c | 15 +++++++++++----
>>   1 file changed, 11 insertions(+), 4 deletions(-)
>>
>> diff --git a/kernel.c b/kernel.c
>> index f4598ea..4b4d789 100644
>> --- a/kernel.c
>> +++ b/kernel.c
>> @@ -10757,11 +10757,18 @@ is_pvops_xen(void)
>>               STREQ(sym, "paravirt_patch_default")))
>>                  return TRUE;
>>
>> -       if (symbol_exists("xen_start_info") &&
>> -           readmem(symbol_value("xen_start_info"), KVADDR, &addr,
>> -           sizeof(void *), "xen_start_info", RETURN_ON_ERROR) &&
>> -           addr != 0)
>> +       if (machine_type("ARM") || machine_type("ARM64")) {
>> +               if (symbol_exists("xen_vcpu_info") &&
>> +                   readmem(symbol_value("xen_vcpu_info"), KVADDR, &addr,
>> +                   sizeof(void *), "xen_vcpu_info", RETURN_ON_ERROR) &&
>> +                   addr != 0)
>> +                       return TRUE;
>> +       } else if (symbol_exists("xen_start_info") &&
>> +                  readmem(symbol_value("xen_start_info"), KVADDR, &addr,
>> +                  sizeof(void *), "xen_start_info", RETURN_ON_ERROR) &&
>> +                  addr != 0) {
>>                  return TRUE;
>> +       }
>>
>>          return FALSE;
>>   }
>> --
>> 2.11.0
> 

-- 
Thanks,
Qi