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Subject: Re: [PATCH v8 2/5] powerpc/hv-24x7: Add rtas call in hv-24x7 driver
 to get processor details
To: Nathan Lynch <nathanl@linux.ibm.com>
References: <20200506110737.14904-1-kjain@linux.ibm.com>
 <20200506110737.14904-3-kjain@linux.ibm.com> <87blmu2nac.fsf@linux.ibm.com>
From: kajoljain <kjain@linux.ibm.com>
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Date: Mon, 18 May 2020 11:02:25 +0530
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On 5/12/20 2:37 AM, Nathan Lynch wrote:
> Hi,
> 
> Kajol Jain <kjain@linux.ibm.com> writes:
>> diff --git a/arch/powerpc/perf/hv-24x7.c b/arch/powerpc/perf/hv-24x7.c
>> index 48e8f4b17b91..8cf242aad98f 100644
>> --- a/arch/powerpc/perf/hv-24x7.c
>> +++ b/arch/powerpc/perf/hv-24x7.c
>> @@ -20,6 +20,7 @@
>>  #include <asm/io.h>
>>  #include <linux/byteorder/generic.h>
>>  
>> +#include <asm/rtas.h>
>>  #include "hv-24x7.h"
>>  #include "hv-24x7-catalog.h"
>>  #include "hv-common.h"
>> @@ -57,6 +58,75 @@ static bool is_physical_domain(unsigned domain)
>>  	}
>>  }
>>  
>> +/*
>> + * The Processor Module Information system parameter allows transferring
>> + * of certain processor module information from the platform to the OS.
>> + * Refer PAPR+ document to get parameter token value as '43'.
>> + */
>> +
>> +#define PROCESSOR_MODULE_INFO   43
>> +#define PROCESSOR_MAX_LENGTH	(8 * 1024)
>> +
>> +DEFINE_SPINLOCK(rtas_local_data_buf_lock);
>> +EXPORT_SYMBOL(rtas_local_data_buf_lock);
> 
> This should be static and not exported, correct?
> 
>> +
>> +static u32 phys_sockets;	/* Physical sockets */
>> +static u32 phys_chipspersocket;	/* Physical chips per socket*/
>> +static u32 phys_coresperchip; /* Physical cores per chip */
>> +
>> +/*
>> + * Function read_sys_info_pseries() make a rtas_call which require
>> + * data buffer of size 8K. As standard 'rtas_data_buf' is of size
>> + * 4K, we are adding new local buffer 'rtas_local_data_buf'.
> 
> Sorry if this has been covered before but I don't understand why it
> would require a larger buffer; by my reading this call will return *ten
> bytes* of output. Also, current versions of PAPR+ limit the output
> length to 4002 bytes. I feel like I'm missing something.
> 

Hi Nathan,
	Thanks for reviewing the patch. Actually when I was testing this patch in
both power8 and power9 machine, I got some issue in power9 because of buffer size.
And I checked the buffer size used in util_linux which is 8192. So, I increase the
buffer size.I will again test it as I did couple of changes after that with 4002 size. 

> 
>> + */
>> +static __be16 rtas_local_data_buf[PROCESSOR_MAX_LENGTH] __cacheline_aligned;
>> +
>> +/*
>> + * read_sys_info_pseries()
>> + * Retrieve the number of sockets and chips per socket and cores per
>> + * chip details through the get-system-parameter rtas call.
>> + */
>> +void read_sys_info_pseries(void)
>> +{
>> +	int call_status, len, ntypes;
>> +
>> +	/*
>> +	 * Making system parameter: chips and sockets and cores per chip
>> +	 * default to 1.
>> +	 */
>> +	phys_sockets = 1;
>> +	phys_chipspersocket = 1;
>> +	phys_coresperchip = 1;
>> +	memset(rtas_local_data_buf, 0, PROCESSOR_MAX_LENGTH * sizeof(__be16));
> 
> Modifying global state outside of any critical section...? How do
> you prevent readers from seeing inconsistent results?

Yes right, Will update.

> 
> 
>> +	spin_lock(&rtas_local_data_buf_lock);
>> +
>> +	call_status = rtas_call(rtas_token("ibm,get-system-parameter"), 3, 1,
>> +				NULL,
>> +				PROCESSOR_MODULE_INFO,
>> +				__pa(rtas_local_data_buf),
>> +				PROCESSOR_MAX_LENGTH);
>> +
>> +	spin_unlock(&rtas_local_data_buf_lock);
> 
> Using this lock this way fails to provide any protection to the data
> buffer or the phys_* variables.
> 
> 
>> +
>> +	if (call_status != 0) {
>> +		pr_info("Error calling get-system-parameter (0x%x)\n",
>> +			call_status);
> 
> To be robust, this should handle busy (-2) and extended delay (990x)
> statuses. And if it's going to log errors it should use pr_err() and use
> decimal, not hex, to report the RTAS call status, since that's how
> they're specified in PAPR+.

Thanks for pointing it, Will update.

Thanks,
Kajol Jain