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Date:   Fri, 14 Jun 2019 09:55:28 -0700
From:   Fenghua Yu <fenghua.yu@...el.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, H Peter Anvin <hpa@...or.com>,
        Christopherson Sean J <sean.j.christopherson@...el.com>,
        Ravi V Shankar <ravi.v.shankar@...el.com>,
        linux-kernel <linux-kernel@...r.kernel.org>, x86 <x86@...nel.org>
Subject: Re: [RFC PATCH 1/3] x86/resctrl: Get max rmid and occupancy scale
 directly from CPUID instead of cpuinfo_x86

On Fri, Jun 14, 2019 at 01:16:33PM +0200, Borislav Petkov wrote:
> On Thu, Jun 13, 2019 at 01:51:02PM -0700, Fenghua Yu wrote:
> > Although x86_cache_max_rmid and x86_cache_occ_scale are read only once
> > during resctrl initialization, they are always stored in cpuinfo_x86 on
> > each CPU during run time even if resctrl is not configured.
> > 
> > To save cpuinfo_x86 space and make CPU and resctrl initialization simpler,
> > remove the two fields from cpuinfo_x86 and get max rmid and occupancy
> > scale directly from CPUID during resctrl initialization. And since each
> > known platform that supports resctrl has same max rmid on all CPUs, no
> > need to scan all CPUs to find minimum of max rmid values, i.e. getting
> > max rmid from CPUID on the current CPU is fine.
> > 
> > Signed-off-by: Fenghua Yu <fenghua.yu@...el.com>
> > ---
> >  arch/x86/include/asm/processor.h       |  3 ---
> >  arch/x86/kernel/cpu/common.c           | 28 --------------------------
> >  arch/x86/kernel/cpu/resctrl/internal.h |  2 +-
> >  arch/x86/kernel/cpu/resctrl/monitor.c  | 28 +++++++++++++++++++++++---
> >  4 files changed, 26 insertions(+), 35 deletions(-)
> > 
> > diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
> > index c34a35c78618..27e875d4ca7d 100644
> > --- a/arch/x86/include/asm/processor.h
> > +++ b/arch/x86/include/asm/processor.h
> > @@ -99,9 +99,6 @@ struct cpuinfo_x86 {
> >  	/* in KB - valid for CPUS which support this call: */
> >  	unsigned int		x86_cache_size;
> >  	int			x86_cache_alignment;	/* In bytes */
> > -	/* Cache QoS architectural values: */
> > -	int			x86_cache_max_rmid;	/* max index */
> > -	int			x86_cache_occ_scale;	/* scale to bytes */
> >  	int			x86_power;
> >  	unsigned long		loops_per_jiffy;
> >  	/* cpuid returned max cores value: */
> > diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
> > index 2c57fffebf9b..38e4b1a9005e 100644
> > --- a/arch/x86/kernel/cpu/common.c
> > +++ b/arch/x86/kernel/cpu/common.c
> > @@ -840,22 +840,9 @@ void get_cpu_cap(struct cpuinfo_x86 *c)
> >  		c->x86_capability[CPUID_F_0_EDX] = edx;
> >  
> >  		if (cpu_has(c, X86_FEATURE_CQM_LLC)) {
> > -			/* will be overridden if occupancy monitoring exists */
> > -			c->x86_cache_max_rmid = ebx;
> > -
> >  			/* QoS sub-leaf, EAX=0Fh, ECX=1 */
> >  			cpuid_count(0x0000000F, 1, &eax, &ebx, &ecx, &edx);
> >  			c->x86_capability[CPUID_F_1_EDX] = edx;
> > -
> > -			if ((cpu_has(c, X86_FEATURE_CQM_OCCUP_LLC)) ||
> > -			      ((cpu_has(c, X86_FEATURE_CQM_MBM_TOTAL)) ||
> > -			       (cpu_has(c, X86_FEATURE_CQM_MBM_LOCAL)))) {
> > -				c->x86_cache_max_rmid = ecx;
> > -				c->x86_cache_occ_scale = ebx;
> > -			}
> > -		} else {
> > -			c->x86_cache_max_rmid = -1;
> > -			c->x86_cache_occ_scale = -1;
> >  		}
> >  	}
> >  
> > @@ -1269,20 +1256,6 @@ static void generic_identify(struct cpuinfo_x86 *c)
> >  #endif
> >  }
> >  
> > -static void x86_init_cache_qos(struct cpuinfo_x86 *c)
> > -{
> > -	/*
> > -	 * The heavy lifting of max_rmid and cache_occ_scale are handled
> > -	 * in get_cpu_cap().  Here we just set the max_rmid for the boot_cpu
> > -	 * in case CQM bits really aren't there in this CPU.
> > -	 */
> > -	if (c != &boot_cpu_data) {
> > -		boot_cpu_data.x86_cache_max_rmid =
> > -			min(boot_cpu_data.x86_cache_max_rmid,
> > -			    c->x86_cache_max_rmid);
> > -	}
> > -}
> > -
> >  /*
> >   * Validate that ACPI/mptables have the same information about the
> >   * effective APIC id and update the package map.
> > @@ -1391,7 +1364,6 @@ static void identify_cpu(struct cpuinfo_x86 *c)
> >  #endif
> >  
> >  	x86_init_rdrand(c);
> > -	x86_init_cache_qos(c);
> >  	setup_pku(c);
> >  
> >  	/*
> > diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h
> > index e49b77283924..474a7090d2dd 100644
> > --- a/arch/x86/kernel/cpu/resctrl/internal.h
> > +++ b/arch/x86/kernel/cpu/resctrl/internal.h
> > @@ -579,7 +579,7 @@ int closids_supported(void);
> >  void closid_free(int closid);
> >  int alloc_rmid(void);
> >  void free_rmid(u32 rmid);
> > -int rdt_get_mon_l3_config(struct rdt_resource *r);
> > +int __init rdt_get_mon_l3_config(struct rdt_resource *r);
> >  void mon_event_count(void *info);
> >  int rdtgroup_mondata_show(struct seq_file *m, void *arg);
> >  void rmdir_mondata_subdir_allrdtgrp(struct rdt_resource *r,
> > diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
> > index 1573a0a6b525..e9d876c25703 100644
> > --- a/arch/x86/kernel/cpu/resctrl/monitor.c
> > +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
> > @@ -617,13 +617,35 @@ static void l3_mon_evt_init(struct rdt_resource *r)
> >  		list_add_tail(&mbm_local_event.list, &r->evt_list);
> >  }
> >  
> > -int rdt_get_mon_l3_config(struct rdt_resource *r)
> > +static void __init get_cqm_info(struct rdt_resource *r)
> > +{
> > +	u32 eax, ebx, ecx, edx;
> > +
> > +	/*
> > +	 * At this point, CQM LLC and one of occupancy, MBM total, and
> > +	 * MBM local monitoring features must be supported.
> > +	 */
> > +	cpuid_count(0x0000000F, 0, &eax, &ebx, &ecx, &edx);
> > +	/* will be overridden if occupancy monitoring exists */
> > +	r->num_rmid = ebx + 1;
> > +
> > +	cpuid_count(0x0000000F, 1, &eax, &ebx, &ecx, &edx);
> 
> Those CPUID accesses should be done *after* testing features, not
> before.
> 
> > +
> > +	if (boot_cpu_has(X86_FEATURE_CQM_OCCUP_LLC))
> 
> That is already done in get_rdt_mon_resources() and rdt_mon_features
> caches those bits. I think you wanna test QOS_L3_OCCUP_EVENT_ID in there

Sure. I can test QOS_L3_OCCUP_EVENT_ID instead of cpuinfo_x86.

> and then read CPUID 0xf and set ->num_rmid.

When this function is called, X86_FEATURE_CQM_LLC must be supported and
one of X86_FEATURE_CQM_OCCUP_LLC, X86_FEATURE_CQM_MBM_LOCAL, and
X86_FEATURE_CQM_MBM_TOTAL must be supported. Otherwise,
get_rdt_mon_resource() is returned before calling rdt_get_mon_l3_config().

So CPUID.f.0 and CPUID.f.1 must be readable and return meaningful
data without testing the features.

But the problem is it's unknown which ones of X86_FEATURE_CQM_OCCUP_LLC,
X86_FEATURE_CQM_MBM_LOCAL, and X86_FEATURE_CQM_MBM_TOTAL are supported.

So after reading CPUID.f.1, test X86_FEATURE_CQM_OCCUP_LLC in order to
override r->num_rmid from ecx. And test X86_FEATURE_CQM_MBM_TOTAL or
X86_FEATURE_CQM_MBM_LOCAL in order to get r>mon_scale from ebx.

Is this sequence OK? If the current sequence is OK, I only need to
change code to test the QOS_L3_*_EVENT_ID, right?

> 
> > +		r->num_rmid = ecx + 1;
> > +
> > +	if (boot_cpu_has(X86_FEATURE_CQM_MBM_TOTAL) || boot_cpu_has(X86_FEATURE_CQM_MBM_LOCAL))
> 
> Ditto.

Thanks.

-Fenghua

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