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

[Qi Zheng]

On 2021/12/20 4:35 PM, Qi Zheng wrote:
> 
> 
> 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.

Like the 'xen_start_info' on the x86 platform:

	- definition:
	struct start_info *xen_start_info;
	EXPORT_SYMBOL_GPL(xen_start_info);

	- initialization:
	startup_xen
	--> mov %rsi, xen_start_info

The 'xen_vcpu_info' on the arm/arm64 platform:

	- definition:
	static struct vcpu_info __percpu *xen_vcpu_info;

	- initialization:
	xen_guest_init
	--> xen_vcpu_info = alloc_percpu(struct vcpu_info);

So I think that it will works well on the arm/arm64 platform. I have
tested it on the arm64 platform(But I can not test it on the arm/arm64
xen machine).

Thanks,
Qi

> 
> 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