Re: [PATCH] perf,x86,p6: Add userspace RDPMC quirk for P6

[Mark Davies]

That fixed it. Booted patched 3.4.78 with CONFIG_APM=y with no problem.

dmesg contains the "Userspace RDPMC support disabled due to a CPU
erratum" message

"cat /sys/devices/cpu/rdpmc" gives "0"

"echo 1 >/sys/devices/cpu/rdpmc" gives "bash: echo: write error: Unknown
error 524" 

Thanks for fixing it. How I missed the return statements in
intel_pmu_init I don't know, probably got a bit over excited when I
spotted what the problem was.

Mark Davies

On Thu, Feb 06 2014, Peter Zijlstra wrote:

> On Thu, Feb 06, 2014 at 07:41:37PM +0000, Mark Davies wrote:
>> Peter
>> 
>> As I reported the problem I thought I better contribute by testing the
>> fix.
>> 
>> I took the patch below and managed to change the 3.4.78 code to match
>> and tried to boot my Pentium Pro system but it hung as before. After
>> some investigation I discovered the quirk is not being run, in fact no
>> quirks were being run in init_hw_perf_events as x86_pmu.quirks was NULL.
>> 
>> The problem as far as I can see is that the quirk is added to x86_pmu in
>> p6_pmu_init but then x86_pmu is reassigned at the end of that function
>> (x86_pmu = p6_pmu) resetting x86_pmu.quirks to NULL.
>
> Right so far.
>
>> x86_pmu looks like
>> it is reassigned again in intel_pmu_init to either core_pmu or intel_pmu
>> after the call to p6_pmu_init so I am not sure which x86_pmu.quirks
>> init_hw_perf_events tries to use.
>
> Note how intel_pmu_init() does: return p6_pmu_init(), so it will never
> get to the x86_pmu assignment for the ARCH_PERFMON drivers.
>
> Yep, thanks for testing and you're (mostly) quite right.
>
> We can do the copy early though, if we return -ENODEV nothing will end
> up using the x86_pmu anyway, so it doesn't matter what lives in there.
>
> ---
> Subject: perf,x86,p6: Add userspace RDPMC quirk for PPro
> From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Date: Wed, 5 Feb 2014 20:48:51 +0100
>
> PPro machines can die hard when PCE gets enabled due to a CPU erratum.
> The safe way it so disable it by default and keep it disabled.
>
> See erratum 26 in:
>
> http://download.intel.com/design/archives/processors/pro/docs/24268935.pdf
>
> Cc: Alan Cox <alan@xxxxxxxxxxxxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: Stephane Eranian <eranian@xxxxxxxxxx>
> Cc: Vince Weaver <vince@xxxxxxxxxx>
> Reported-by: Mark Davies <junk@xxxxxxxxxxx>
> Signed-off-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> ---
>  arch/x86/kernel/cpu/perf_event.c    |    6 +++-
>  arch/x86/kernel/cpu/perf_event.h    |    1 
>  arch/x86/kernel/cpu/perf_event_p6.c |   48 ++++++++++++++++++++++++------------
>  3 files changed, 39 insertions(+), 16 deletions(-)
>
> --- a/arch/x86/kernel/cpu/perf_event.c
> +++ b/arch/x86/kernel/cpu/perf_event.c
> @@ -1521,6 +1521,8 @@ static int __init init_hw_perf_events(vo
>  
>  	pr_cont("%s PMU driver.\n", x86_pmu.name);
>  
> +	x86_pmu.attr_rdpmc = 1; /* enable userspace RDPMC usage by default */
> +
>  	for (quirk = x86_pmu.quirks; quirk; quirk = quirk->next)
>  		quirk->func();
>  
> @@ -1534,7 +1536,6 @@ static int __init init_hw_perf_events(vo
>  		__EVENT_CONSTRAINT(0, (1ULL << x86_pmu.num_counters) - 1,
>  				   0, x86_pmu.num_counters, 0, 0);
>  
> -	x86_pmu.attr_rdpmc = 1; /* enable userspace RDPMC usage by default */
>  	x86_pmu_format_group.attrs = x86_pmu.format_attrs;
>  
>  	if (x86_pmu.event_attrs)
> @@ -1820,6 +1821,9 @@ static ssize_t set_attr_rdpmc(struct dev
>  	if (ret)
>  		return ret;
>  
> +	if (x86_pmu.attr_rdpmc_broken)
> +		return -ENOTSUPP;
> +
>  	if (!!val != !!x86_pmu.attr_rdpmc) {
>  		x86_pmu.attr_rdpmc = !!val;
>  		smp_call_function(change_rdpmc, (void *)val, 1);
> --- a/arch/x86/kernel/cpu/perf_event.h
> +++ b/arch/x86/kernel/cpu/perf_event.h
> @@ -409,6 +409,7 @@ struct x86_pmu {
>  	/*
>  	 * sysfs attrs
>  	 */
> +	int		attr_rdpmc_broken;
>  	int		attr_rdpmc;
>  	struct attribute **format_attrs;
>  	struct attribute **event_attrs;
> --- a/arch/x86/kernel/cpu/perf_event_p6.c
> +++ b/arch/x86/kernel/cpu/perf_event_p6.c
> @@ -231,31 +231,49 @@ static __initconst const struct x86_pmu
>  
>  };
>  
> +static __init void p6_pmu_rdpmc_quirk(void)
> +{
> +	if (boot_cpu_data.x86_mask < 9) {
> +		/*
> +		 * PPro erratum 26; fixed in stepping 9 and above.
> +		 */
> +		pr_warn("Userspace RDPMC support disabled due to a CPU erratum\n");
> +		x86_pmu.attr_rdpmc_broken = 1;
> +		x86_pmu.attr_rdpmc = 0;
> +	}
> +}
> +
>  __init int p6_pmu_init(void)
>  {
> +	x86_pmu = p6_pmu;
> +
>  	switch (boot_cpu_data.x86_model) {
> -	case 1:
> -	case 3:  /* Pentium Pro */
> -	case 5:
> -	case 6:  /* Pentium II */
> -	case 7:
> -	case 8:
> -	case 11: /* Pentium III */
> -	case 9:
> -	case 13:
> -		/* Pentium M */
> +	case  1: /* Pentium Pro */
> +		x86_add_quirk(p6_pmu_rdpmc_quirk);
> +		break;
> +
> +	case  3: /* Pentium II - Klamath */
> +	case  5: /* Pentium II - Deschutes */
> +	case  6: /* Pentium II - Mendocino */
>  		break;
> +
> +	case  7: /* Pentium III - Katmai */
> +	case  8: /* Pentium III - Coppermine */
> +	case 10: /* Pentium III Xeon */
> +	case 11: /* Pentium III - Tualatin */
> +		break;
> +
> +	case  9: /* Pentium M - Banias */
> +	case 13: /* Pentium M - Dothan */
> +		break;
> +
>  	default:
> -		pr_cont("unsupported p6 CPU model %d ",
> -			boot_cpu_data.x86_model);
> +		pr_cont("unsupported p6 CPU model %d ", boot_cpu_data.x86_model);
>  		return -ENODEV;
>  	}
>  
> -	x86_pmu = p6_pmu;
> -
>  	memcpy(hw_cache_event_ids, p6_hw_cache_event_ids,
>  		sizeof(hw_cache_event_ids));
>  
> -
>  	return 0;
>  }
--
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