Re: [PATCH 2/2] x86/resctrl: Support CPUID enumeration of MBM counter width

[Reinette Chatre]

Hi Borislav,

On 4/30/2020 2:59 AM, Borislav Petkov wrote:
> On Wed, Apr 29, 2020 at 11:42:03AM -0700, Reinette Chatre wrote:
>> This would essentially be resubmitting [1] though. Do you expect that
>> this change would receive a different reception at this time?
> 
> Right, Thomas and I talked it over a bit last night. So the proper
> thing to do is to read all that information *once* and put it in
> boot_cpu_data. Because that information is replicated the same over
> CPUID on each core. If there's per-CPU stuff, then it should remain
> per-CPU but looking at how the RDT code uses boot_cpu_data, I'd say this
> is global info.
> 
> So, it should be parsed once on the BSP during boot and put into
> boot_cpu_data. And then silly stuff like x86_init_cache_qos() should go
> away too.

You are correct. I looked through the hardware errata and confirmed with
a few people very knowledgeable about the history and technical details
of CMT that x86_init_cache_qos() is not necessary. There exists no
platform where the CPUs on a platform that support CMT either does not
report a RMID or report different RMID.

Also, for the existing implementation moving init_cqm() to
early_identify_cpu() makes sense for all the reasons you mention.

I am struggling with what should follow ...

> 
> If this info is needed on Intel only, then it should be parsed in
> cpu/intel.c, in a ->c_bsp_init helper and if it is needed on AMD too,
> then a function which does this should be called by the respective
> c_bsp_init helper.

Using c_bsp_init may be needed to obtain the Intel-only property that
the patch that started this originally attempted to do. AMD and Intel
support the same CPUID leaf and two sub-leaves ... only differing in the
one new register that is defined for Intel but undefined for AMD.

I am concerned with how I am interpreting your suggestion here since my
interpretation does end up with duplicate code between the two
c_bsp_init helpers. Below is this snippet - is this how you envisioned
this change? (Please note that in this snippet you would find init_cqm()
moved from early_identify_cpu(), this change is thus done with the
assumption that your earlier suggestions have all been applied already.)

diff --git a/arch/x86/include/asm/processor.h
b/arch/x86/include/asm/processor.h
index 3bcf27caf6c9..76f86fdb02af 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -116,6 +116,7 @@ struct cpuinfo_x86 {
 	/* Cache QoS architectural values: */
 	int			x86_cache_max_rmid;	/* max index */
 	int			x86_cache_occ_scale;	/* scale to bytes */
+	int			x86_cache_mbm_width_offset;
 	int			x86_power;
 	unsigned long		loops_per_jiffy;
 	/* cpuid returned max cores value: */
diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index 547ad7bbf0e0..2e6c718ba793 100644
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -512,6 +512,38 @@ static void early_init_amd_mc(struct cpuinfo_x86 *c)
 #endif
 }

+/*
+ * Significant overlap with the Intel initialization found in
+ * init_llc_monitoring_intel() since CPUID leaf 0xF subleaf 0x1
+ * differ in all but one register (used to initialize
+ * x86_cache_mbm_width_offset) that is undefined on AMD.
+ */
+static void init_llc_monitoring_amd(struct cpuinfo_x86 *c)
+{
+	if (!cpu_has(c, X86_FEATURE_CQM_LLC)) {
+		c->x86_cache_max_rmid  = -1;
+		c->x86_cache_occ_scale = -1;
+		c->x86_cache_mbm_width_offset = -1;
+		return;
+	}
+
+	/* will be overridden if occupancy monitoring exists */
+	c->x86_cache_max_rmid = cpuid_ebx(0xf);
+
+	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)) {
+		u32 eax, ebx, ecx, edx;
+
+		/* QoS sub-leaf, EAX=0Fh, ECX=1 */
+		cpuid_count(0xf, 1, &eax, &ebx, &ecx, &edx);
+
+		c->x86_cache_max_rmid  = ecx;
+		c->x86_cache_occ_scale = ebx;
+		c->x86_cache_mbm_width_offset = -1;
+	}
+}
+
 static void bsp_init_amd(struct cpuinfo_x86 *c)
 {

@@ -597,6 +629,8 @@ static void bsp_init_amd(struct cpuinfo_x86 *c)
 			x86_amd_ls_cfg_ssbd_mask = 1ULL << bit;
 		}
 	}
+
+	init_llc_monitoring_amd(c);
 }

 static void early_detect_mem_encrypt(struct cpuinfo_x86 *c)
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 3151a366b0a8..d07809286b95 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -854,30 +854,6 @@ static void init_speculation_control(struct
cpuinfo_x86 *c)
 	}
 }

-static void init_cqm(struct cpuinfo_x86 *c)
-{
-	if (!cpu_has(c, X86_FEATURE_CQM_LLC)) {
-		c->x86_cache_max_rmid  = -1;
-		c->x86_cache_occ_scale = -1;
-		return;
-	}
-
-	/* will be overridden if occupancy monitoring exists */
-	c->x86_cache_max_rmid = cpuid_ebx(0xf);
-
-	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)) {
-		u32 eax, ebx, ecx, edx;
-
-		/* QoS sub-leaf, EAX=0Fh, ECX=1 */
-		cpuid_count(0xf, 1, &eax, &ebx, &ecx, &edx);
-
-		c->x86_cache_max_rmid  = ecx;
-		c->x86_cache_occ_scale = ebx;
-	}
-}
-
 void get_cpu_cap(struct cpuinfo_x86 *c)
 {
 	u32 eax, ebx, ecx, edx;
@@ -1212,7 +1188,6 @@ static void __init early_identify_cpu(struct
cpuinfo_x86 *c)

 		c->cpu_index = 0;
 		filter_cpuid_features(c, false);
-		init_cqm(c);

 		if (this_cpu->c_bsp_init)
 			this_cpu->c_bsp_init(c);
diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
index bf08d4508ecb..0775090bd5e2 100644
--- a/arch/x86/kernel/cpu/intel.c
+++ b/arch/x86/kernel/cpu/intel.c
@@ -322,6 +322,46 @@ static void early_init_intel(struct cpuinfo_x86 *c)
 		detect_ht_early(c);
 }

+/*
+ * Significant overlap with the AMD initialization found in
+ * init_llc_monitoring_amd() since CPUID leaf 0xF subleaf 0x1
+ * differ in all but one register (used to initialize
+ * x86_cache_mbm_width_offset) that is undefined on AMD.
+ */
+static void init_llc_monitoring_intel(struct cpuinfo_x86 *c)
+{
+	if (!cpu_has(c, X86_FEATURE_CQM_LLC)) {
+		c->x86_cache_max_rmid  = -1;
+		c->x86_cache_occ_scale = -1;
+		c->x86_cache_mbm_width_offset = -1;
+		return;
+	}
+
+	/* will be overridden if occupancy monitoring exists */
+	c->x86_cache_max_rmid = cpuid_ebx(0xf);
+
+	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)) {
+		u32 eax, ebx, ecx, edx;
+
+		/* QoS sub-leaf, EAX=0Fh, ECX=1 */
+		cpuid_count(0xf, 1, &eax, &ebx, &ecx, &edx);
+
+		c->x86_cache_max_rmid  = ecx;
+		c->x86_cache_occ_scale = ebx;
+		c->x86_cache_mbm_width_offset = eax & 0xff;
+	}
+}
+
+/*
+ * Initialization work to be done only once during boot.
+ */
+static void bsp_init_intel(struct cpuinfo_x86 *c)
+{
+	init_llc_monitoring_intel(c);
+}
+
 #ifdef CONFIG_X86_32
 /*
  *	Early probe support logic for ppro memory erratum #50
@@ -961,6 +1001,7 @@ static const struct cpu_dev intel_cpu_dev = {
 #endif
 	.c_detect_tlb	= intel_detect_tlb,
 	.c_early_init   = early_init_intel,
+	.c_bsp_init	= bsp_init_intel,
 	.c_init		= init_intel,
 	.c_x86_vendor	= X86_VENDOR_INTEL,
 };

> 
> Then all its users can continue reading it out of boot_cpu_data and
> future RDT hw info can be added there.

Understood.

Thank you very much

Reinette