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Date: Fri, 3 Feb 2023 11:12:35 +0800
From: silviazhaooc <silviazhao-oc@...oxin.com>
To: Kevin Brace <kevinbrace@....com>
CC: <peterz@...radead.org>, <mingo@...hat.com>, <acme@...nel.org>,
<mark.rutland@....com>, <alexander.shishkin@...ux.intel.com>,
<jolsa@...nel.org>, <namhyung@...nel.org>, <tglx@...utronix.de>,
<bp@...en8.de>, <dave.hansen@...ux.intel.com>, <x86@...nel.org>,
<hpa@...or.com>, <linux-perf-users@...r.kernel.org>,
<linux-kernel@...r.kernel.org>, <cobechen@...oxin.com>,
<louisqi@...oxin.com>, <silviazhao@...oxin.com>,
<tonywwang@...oxin.com>, <8vvbbqzo567a@...pam.xutrox.com>
Subject: Re: [PATCH] x86/perf/zhaoxin: Add stepping check for ZX-C
Hi Kevin,
Thanks for your kindly reply.
Since VIA Nano 1000/2000/3000 series are really very old CPU, and we
can't find related mainboard for full verification. We suggest not to
support all Nano series for PMC driver.
On 2023/2/3 07:53, Kevin Brace wrote:
> Hi Silvia,
>
> Thank you very much for resending the VIA / Zhaoxin PMU patch and for keeping me in the loop.
> I observed this bug on ECS (Elitegroup Computer Systems) VX900-I mainboard.
> The mainboard contains one VIA Nano L2007 processor (1.6 GHz) soldered on the PCB.
> Although I have not independently verified it, CPUID steppings for VIA Nano 1000 / 2000 series (Centaur Technology code name: CNA) are supposedly 2 and 3.
> CPUID stepppings for VIA Nano 3000 series (Centaur Technology code name: CNB) is 8.
> CPUID stepppings for VIA Nano x2 (Centaur Technology code name: CNC) is 10.
>
> https://www.reddit.com/r/VIA/comments/dy71bn/via_centaurs_new_cpu_is_a_8core_x86_cpu_with_an/
>
> I have not checked the actual CPUID steppings, but I have confirmed that the current code without the fix works okay with Nano 3000 series and Nano x2, but definitely not Nano 2000 series.
> For Nano 3000 series test, I used VIA Embedded EPIA M830 mainboard.
> For Nano x2 test, I used HP T510 thin client.
> Based on my observations, it appears that Centaur CNA contains a bug reading some performance counters, so not to cause inconveniences with users of Nano 1000 / 2000 series processors, the patch should limit / prevent reading performance counters on these processors.
> I think the code for the fix should reflect this the following way.
>
> _______________________________________________________________
> switch (boot_cpu_data.x86) {
> case 0x06:
> - if (boot_cpu_data.x86_model == 0x0f || boot_cpu_data.x86_model == 0x19) {
> + if ((boot_cpu_data.x86_model == 0x0f && boot_cpu_data.x86_stepping >= 0x08) ||
> + boot_cpu_data.x86_model == 0x19) {
>
> x86_pmu.max_period = x86_pmu.cntval_mask >> 1;
>
> _______________________________________________________________
>
> The above code should exclude Nano 1000 / 2000 series processors properly.
> I lost easy access to ECS VX900-I mainboard for now (I need to look around for it. I do own another copy of it.), so I cannot confirm if the fix is properly working.
> I still have easy access to EPIA M830 mainboard.
> I welcome anyone's feedback on this issue.
> This fix should go into the current kernel in development since it is a show stopper for users of Nano 1000 / 2000 series processors.
> If the fix is adopted, please backport it to previous releases of the kernel.
> I wasted about 2 weeks on this issue, and this fix should have never been ignored for such a long time.
>
> Regards,
>
> Kevin Brace
> Brace Computer Laboratory blog
> https://bracecomputerlab.com
>
>
>> Sent: Thursday, February 02, 2023 at 3:17 AM
>> From: "silviazhao-oc" <silviazhao-oc@...oxin.com>
>> To: peterz@...radead.org, mingo@...hat.com, acme@...nel.org, mark.rutland@....com, alexander.shishkin@...ux.intel.com, jolsa@...nel.org, namhyung@...nel.org, tglx@...utronix.de, bp@...en8.de, dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com, linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
>> Cc: cobechen@...oxin.com, louisqi@...oxin.com, silviazhao@...oxin.com, tonywwang@...oxin.com, kevinbrace@....com, 8vvbbqzo567a@...pam.xutrox.com
>> Subject: [PATCH] x86/perf/zhaoxin: Add stepping check for ZX-C
>>
>> Nano processor may not fully support rdpmc instruction, it works well
>> for reading general pmc counter, but will lead GP(general protection)
>> when accessing fixed pmc counter. Furthermore, family/mode information
>> is same between Nano processor and ZX-C processor, it leads to zhaoxin
>> pmu driver is wrongly loaded for Nano processor, which resulting boot
>> kernal fail.
>>
>> To solve this problem, stepping information will be checked to distinguish
>> between Nano processor and ZX-C processor.
>>
>> Fixes: 3a4ac121c2ca (“x86/perf: Add hardware performance events support for Zhaoxin CPU”)
>> Reported-by: Arjan <8vvbbqzo567a@...pam.xutrox.com>
>> Link: https://bugzilla.kernel.org/show_bug.cgi?id=212389
>> Reported-by: Kevin Brace <kevinbrace@....com>
>>
>> Signed-off-by: silviazhao-oc <silviazhao-oc@...oxin.com>
>> ---
>> arch/x86/events/zhaoxin/core.c | 3 ++-
>> 1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/x86/events/zhaoxin/core.c b/arch/x86/events/zhaoxin/core.c
>> index 949d845c922b..cef1de251613 100644
>> --- a/arch/x86/events/zhaoxin/core.c
>> +++ b/arch/x86/events/zhaoxin/core.c
>> @@ -541,7 +541,8 @@ __init int zhaoxin_pmu_init(void)
>>
>> switch (boot_cpu_data.x86) {
>> case 0x06:
>> - if (boot_cpu_data.x86_model == 0x0f || boot_cpu_data.x86_model == 0x19) {
>> + if ((boot_cpu_data.x86_model == 0x0f && boot_cpu_data.x86_stepping >= 0x0e) ||
>> + boot_cpu_data.x86_model == 0x19) {
>>
>> x86_pmu.max_period = x86_pmu.cntval_mask >> 1;
>>
>> --
>> 2.17.1
>>
>>
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