x86/intel_rdt: Discover supported platforms via prefetch disable bits

Knowing the model specific prefetch disable bits is required to support
cache pseudo-locking because the hardware prefetchers need to be disabled
when the kernel memory is pseudo-locked to cache. We add these bits only
for platforms known to support cache pseudo-locking.

When the user requests locksetup mode to be entered it will fail if the
prefetch disabling bits are not known for the platform.

Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: fenghua.yu@intel.com
Cc: tony.luck@intel.com
Cc: vikas.shivappa@linux.intel.com
Cc: gavin.hindman@intel.com
Cc: jithu.joseph@intel.com
Cc: dave.hansen@intel.com
Cc: hpa@zytor.com
Link: https://lkml.kernel.org/r/3eef559aa9fd693a104ff99ff909cfee450c1695.1529706536.git.reinette.chatre@intel.com

diff --git a/arch/x86/kernel/cpu/intel_rdt_pseudo_lock.c b/arch/x86/kernel/cpu/intel_rdt_pseudo_lock.c
index b145a7386b10b322c6ceb8da3e888efdc4c21aef..cbba4bc17522a8a0e7e59e076973c53894a3248c 100644 (file)
--- a/arch/x86/kernel/cpu/intel_rdt_pseudo_lock.c
+++ b/arch/x86/kernel/cpu/intel_rdt_pseudo_lock.c
@@ -12,8 +12,73 @@
 #define pr_fmt(fmt)    KBUILD_MODNAME ": " fmt
 
 #include <linux/slab.h>
+#include <asm/intel-family.h>
 #include "intel_rdt.h"
 
+/*
+ * MSR_MISC_FEATURE_CONTROL register enables the modification of hardware
+ * prefetcher state. Details about this register can be found in the MSR
+ * tables for specific platforms found in Intel's SDM.
+ */
+#define MSR_MISC_FEATURE_CONTROL       0x000001a4
+
+/*
+ * The bits needed to disable hardware prefetching varies based on the
+ * platform. During initialization we will discover which bits to use.
+ */
+static u64 prefetch_disable_bits;
+
+/**
+ * get_prefetch_disable_bits - prefetch disable bits of supported platforms
+ *
+ * Capture the list of platforms that have been validated to support
+ * pseudo-locking. This includes testing to ensure pseudo-locked regions
+ * with low cache miss rates can be created under variety of load conditions
+ * as well as that these pseudo-locked regions can maintain their low cache
+ * miss rates under variety of load conditions for significant lengths of time.
+ *
+ * After a platform has been validated to support pseudo-locking its
+ * hardware prefetch disable bits are included here as they are documented
+ * in the SDM.
+ *
+ * Return:
+ * If platform is supported, the bits to disable hardware prefetchers, 0
+ * if platform is not supported.
+ */
+static u64 get_prefetch_disable_bits(void)
+{
+       if (boot_cpu_data.x86_vendor != X86_VENDOR_INTEL ||
+           boot_cpu_data.x86 != 6)
+               return 0;
+
+       switch (boot_cpu_data.x86_model) {
+       case INTEL_FAM6_BROADWELL_X:
+               /*
+                * SDM defines bits of MSR_MISC_FEATURE_CONTROL register
+                * as:
+                * 0    L2 Hardware Prefetcher Disable (R/W)
+                * 1    L2 Adjacent Cache Line Prefetcher Disable (R/W)
+                * 2    DCU Hardware Prefetcher Disable (R/W)
+                * 3    DCU IP Prefetcher Disable (R/W)
+                * 63:4 Reserved
+                */
+               return 0xF;
+       case INTEL_FAM6_ATOM_GOLDMONT:
+       case INTEL_FAM6_ATOM_GEMINI_LAKE:
+               /*
+                * SDM defines bits of MSR_MISC_FEATURE_CONTROL register
+                * as:
+                * 0     L2 Hardware Prefetcher Disable (R/W)
+                * 1     Reserved
+                * 2     DCU Hardware Prefetcher Disable (R/W)
+                * 63:3  Reserved
+                */
+               return 0x5;
+       }
+
+       return 0;
+}
+
 /**
  * pseudo_lock_init - Initialize a pseudo-lock region
  * @rdtgrp: resource group to which new pseudo-locked region will belong
@@ -225,6 +290,16 @@ int rdtgroup_locksetup_enter(struct rdtgroup *rdtgrp)
                return -EINVAL;
        }
 
+       /*
+        * Not knowing the bits to disable prefetching implies that this
+        * platform does not support Cache Pseudo-Locking.
+        */
+       prefetch_disable_bits = get_prefetch_disable_bits();
+       if (prefetch_disable_bits == 0) {
+               rdt_last_cmd_puts("pseudo-locking not supported\n");
+               return -EINVAL;
+       }
+
        if (rdtgroup_monitor_in_progress(rdtgrp)) {
                rdt_last_cmd_puts("monitoring in progress\n");
                return -EINVAL;