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

[Qi Zheng]

On 12/15/21 3:42 PM, HAGIO KAZUHITO(萩尾 一仁) wrote:
> Hi Qi, Xen folks,
> 
> -----Original Message-----
>> 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 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"
>>
>> Fix it by using xen_vcpu_id instead of xen_start_info to detect Xen dumps.
>>
>> Signed-off-by: Qi Zheng <zhengqi.arch at bytedance.com>
>> ---
>>   kernel.c | 21 ++++++++++++++++-----
>>   1 file changed, 16 insertions(+), 5 deletions(-)
>>
>> diff --git a/kernel.c b/kernel.c
>> index f4598ea..b216fbe 100644
>> --- a/kernel.c
>> +++ b/kernel.c
>> @@ -10745,6 +10745,9 @@ is_pvops_xen(void)
>>   {
>>   	ulong addr;
>>   	char *sym;
>> +	struct syment * sp;
>> +	ulong ptr;
>> +	int i;
>>
>>   	if (!PVOPS())
>>   		return FALSE;
>> @@ -10757,11 +10760,19 @@ 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)
>> -		return TRUE;
>> +	sp = per_cpu_symbol_search("xen_vcpu_id");
>> +	if (sp) {
>> +		for (i = 0; i < NR_CPUS; i++) {
>> +			if (!kt->__per_cpu_offset[i])
>> +				continue;
> 
> Thanks for the patch.
> 
> But seems that kt->__per_cpu_offset is initialized after the is_pvops_xen()
> call.  So this block always return FALSE?
> 
> Is there any other variable that we can use?  or another solution..

Or use xen_vcpu_info for arm/arm64 machine and xen_start_info for x86
machine? Both of these variables are assigned during the initialization 
path.

Thanks,
Qi

> 
> Thanks,
> Kazu
> 
>> +
>> +			ptr = sp->value + kt->__per_cpu_offset[i];
>> +			if (ptr && readmem(ptr, KVADDR, &ptr, sizeof(uint32_t),
>> +			    "xen_vcpu_id", FAULT_ON_ERROR))
>> +				return TRUE;
>> +			return FALSE;
>> +		}
>> +	}
>>
>>   	return FALSE;
>>   }
>> --
>> 2.11.0

-- 
Thanks,
Qi