[PATCH 6/7] x86/intel_rdt: Intel haswell Cache Allocation enumeration

[Vikas Shivappa]

Cache Allocation on hsw needs to be enumerated
separately as HSW does not have support for CPUID enumeration for Cache
Allocation. Cache Allocation is only supported on certain HSW SKUs. This
patch does a probe test for hsw CPUs by writing a CLOSid(Class of
    service id) into high 32 bits of IA32_PQR_MSR and see if the bits
stick. The probe test is only done after confirming that the CPU is HSW.
Other HSW specific quirks are:
-HSW requires the L3 cache bit mask to be at least two bits.
-Maximum CLOSids supported is always 4.
-Maximum bits support in cache bit mask is always 20.

Signed-off-by: Vikas Shivappa <vikas.shivappa@xxxxxxxxxxxxxxx>
---
 arch/x86/kernel/cpu/intel_rdt.c | 63 +++++++++++++++++++++++++++++++++++++++--
 1 file changed, 60 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/cpu/intel_rdt.c b/arch/x86/kernel/cpu/intel_rdt.c
index 2415965..0abb0f6 100644
--- a/arch/x86/kernel/cpu/intel_rdt.c
+++ b/arch/x86/kernel/cpu/intel_rdt.c
@@ -39,6 +39,11 @@ struct static_key __read_mostly rdt_enable_key = STATIC_KEY_INIT_FALSE;
 DEFINE_PER_CPU(unsigned int, x86_cpu_clos);
 
 /*
+ * Minimum bits required in Cache bitmask.
+ */
+static unsigned int min_bitmask_len = 1;
+
+/*
  * Mask of CPUs for writing CBM values. We only need one per-socket.
  */
 static cpumask_t rdt_cpumask;
@@ -46,6 +51,57 @@ static cpumask_t rdt_cpumask;
 #define rdt_for_each_child(pos_css, parent_ir)		\
 	css_for_each_child((pos_css), &(parent_ir)->css)
 
+/*
+ * hsw_probetest() - Have to do probe
+ * test for Intel haswell CPUs as it does not have
+ * CPUID enumeration support for Cache allocation.
+ *
+ * Probes by writing to the high 32 bits(CLOSid)
+ * of the IA32_PQR_MSR and testing if the bits stick.
+ * Then hardcode the max CLOS and max bitmask length on hsw.
+ * The minimum cache bitmask length allowed for HSW is 2 bits.
+ */
+static inline bool hsw_probetest(void)
+{
+	u32 l, h_old, h_new, h_tmp;
+
+	if (rdmsr_safe(MSR_IA32_PQR_ASSOC, &l, &h_old))
+		return false;
+
+	/*
+	 * Default value is always 0 if feature is present.
+	 */
+	h_tmp = h_old ^ 0x1U;
+	if (wrmsr_safe(MSR_IA32_PQR_ASSOC, l, h_tmp) ||
+	    rdmsr_safe(MSR_IA32_PQR_ASSOC, &l, &h_new))
+		return false;
+
+	if (h_tmp != h_new)
+		return false;
+
+	wrmsr_safe(MSR_IA32_PQR_ASSOC, l, h_old);
+
+	boot_cpu_data.x86_rdt_max_closid = 4;
+	boot_cpu_data.x86_rdt_max_cbm_len = 20;
+	min_bitmask_len = 2;
+
+	return true;
+}
+
+static inline bool intel_cache_alloc_supported(struct cpuinfo_x86 *c)
+{
+	if (cpu_has(c, X86_FEATURE_CAT_L3))
+		return true;
+
+	/*
+	 * Probe test for Haswell CPUs.
+	 */
+	if (c->x86 == 0x6 && c->x86_model == 0x3f)
+		return hsw_probetest();
+
+	return false;
+}
+
 static void __clos_init(unsigned int closid)
 {
 	struct clos_cbm_map *ccm = &ccmap[closid];
@@ -170,7 +226,7 @@ static inline bool cbm_is_contiguous(unsigned long var)
 	unsigned long maxcbm = MAX_CBM_LENGTH;
 	unsigned long first_bit, zero_bit;
 
-	if (!var)
+	if (bitmap_weight(&var, maxcbm) < min_bitmask_len)
 		return false;
 
 	first_bit = find_next_bit(&var, maxcbm, 0);
@@ -199,7 +255,8 @@ static int validate_cbm(struct intel_rdt *ir, unsigned long cbmvalue)
 	int err = 0;
 
 	if (!cbm_is_contiguous(cbmvalue)) {
-		pr_err("bitmask should have >= 1 bit and be contiguous\n");
+		pr_err("bitmask should have >=%d bits and be contiguous\n",
+			 min_bitmask_len);
 		err = -EINVAL;
 		goto out_err;
 	}
@@ -431,7 +488,7 @@ static int __init intel_rdt_late_init(void)
 	static struct clos_cbm_map *ccm;
 	size_t sizeb;
 
-	if (!cpu_has(c, X86_FEATURE_CAT_L3)) {
+	if (!intel_cache_alloc_supported(c)) {
 		rdt_root_group.css.ss->disabled = 1;
 		return -ENODEV;
 	}
-- 
1.9.1

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/