[PATCH v2] drm/i915/tgl: Add sysfs interface to control class-of-service

[Prathap Kumar Valsan <prathap.kumar.valsan@intel.com>]

To provide shared last-level-cache isolation to cpu workloads running
concurrently with gpu workloads, the gpu allocation of cache lines needs
to be restricted to certain ways. Currently GPU hardware supports four
class-of-service(CLOS) levels and there is an associated way-mask for
each CLOS.

Hardware supports reading supported way-mask configuration for GPU using
a bios pcode interface. The supported way-masks and the one currently
active is communicated to userspace via a sysfs file--closctrl. Admin user
can then select a new mask by writing the mask value to the file.

Note of Caution: Restricting cache ways using this mechanism presents a
larger attack surface for side-channel attacks.

Example usage:
The active way-mask is highlighted within square brackets.
> cat /sys/class/drm/card0/closctrl
[0xffff] 0xff00 0xc000 0x8000

CLOS0 is currently active.

> echo 0x8000 > /sys/class/drm/card0/closctrl
> cat /sys/class/drm/card0/closctrl
0xffff 0xff00 0xc000 [0x8000]

CLOS3 is currently active

Signed-off-by: Prathap Kumar Valsan <prathap.kumar.valsan@intel.com>
---
Changes in v2:
Declare closctrl_show and closctrl_store as static functions.
 drivers/gpu/drm/i915/gt/intel_mocs.c | 57 ++++++++++++++++++++---
 drivers/gpu/drm/i915/gt/intel_mocs.h |  1 +
 drivers/gpu/drm/i915/i915_drv.h      |  8 ++++
 drivers/gpu/drm/i915/i915_reg.h      |  1 +
 drivers/gpu/drm/i915/i915_sysfs.c    | 67 ++++++++++++++++++++++++++++
 5 files changed, 129 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/i915/gt/intel_mocs.c b/drivers/gpu/drm/i915/gt/intel_mocs.c
index 728704bbbe18..dd13e61944fd 100644
--- a/drivers/gpu/drm/i915/gt/intel_mocs.c
+++ b/drivers/gpu/drm/i915/gt/intel_mocs.c
@@ -26,6 +26,7 @@
 #include "intel_gt.h"
 #include "intel_mocs.h"
 #include "intel_lrc.h"
+#include "intel_sideband.h"
 
 /* structures required */
 struct drm_i915_mocs_entry {
@@ -51,6 +52,7 @@ struct drm_i915_mocs_table {
 #define LE_SCF(value)		((value) << 14)
 #define LE_COS(value)		((value) << 15)
 #define LE_SSE(value)		((value) << 17)
+#define LE_COS_MASK		GENMASK(16, 15)
 
 /* Defines for the tables (LNCFMOCS0 - LNCFMOCS31) - two entries per word */
 #define L3_ESC(value)		((value) << 0)
@@ -408,10 +410,13 @@ void intel_mocs_init_engine(struct intel_engine_cs *engine)
 				      unused_value);
 }
 
-static void intel_mocs_init_global(struct intel_gt *gt)
+void intel_mocs_init_global(struct intel_gt *gt)
 {
+	struct drm_i915_private *i915 = gt->i915;
 	struct intel_uncore *uncore = gt->uncore;
 	struct drm_i915_mocs_table table;
+	unsigned int active_clos;
+	u32 value, unused_value;
 	unsigned int index;
 
 	GEM_BUG_ON(!HAS_GLOBAL_MOCS_REGISTERS(gt->i915));
@@ -422,20 +427,31 @@ static void intel_mocs_init_global(struct intel_gt *gt)
 	if (GEM_DEBUG_WARN_ON(table.size > table.n_entries))
 		return;
 
-	for (index = 0; index < table.size; index++)
+	active_clos = atomic_read(&i915->clos.active_clos);
+
+	for (index = 0; index < table.size; index++) {
+		value = table.table[index].control_value;
+		value &= ~LE_COS_MASK;
+		value |= FIELD_PREP(LE_COS_MASK, active_clos);
+
 		intel_uncore_write(uncore,
 				   GEN12_GLOBAL_MOCS(index),
-				   table.table[index].control_value);
+				   value);
+	}
 
 	/*
 	 * Ok, now set the unused entries to the invalid entry (index 0). These
 	 * entries are officially undefined and no contract for the contents and
 	 * settings is given for these entries.
 	 */
+	unused_value = table.table[0].control_value;
+	unused_value &= ~LE_COS_MASK;
+	unused_value |= FIELD_PREP(LE_COS_MASK, active_clos);
+
 	for (; index < table.n_entries; index++)
 		intel_uncore_write(uncore,
 				   GEN12_GLOBAL_MOCS(index),
-				   table.table[0].control_value);
+				   unused_value);
 }
 
 static int emit_mocs_control_table(struct i915_request *rq,
@@ -625,10 +641,41 @@ int intel_mocs_emit(struct i915_request *rq)
 	return 0;
 }
 
+static void intel_read_clos_way_mask(struct intel_gt *gt)
+{
+	struct drm_i915_private *i915 = gt->i915;
+	struct drm_i915_mocs_table table;
+	int ret, i;
+	u32 val;
+
+	if (!get_mocs_settings(gt, &table))
+		return;
+
+	/* COS is same for all entries */
+	atomic_set(&i915->clos.active_clos,
+		   FIELD_GET(LE_COS_MASK, get_entry_control(&table, 0)));
+	for (i = 0; i < NUM_OF_CLOS; i++) {
+		val = i;
+		ret = sandybridge_pcode_read(i915,
+					     ICL_PCODE_LLC_COS_WAY_MASK_INFO,
+					     &val, NULL);
+		if (ret) {
+			DRM_ERROR("Mailbox read error = %d\n", ret);
+			return;
+		}
+
+		i915->clos.way_mask[i] = val;
+	}
+
+	i915->clos.support_way_mask_read = true;
+}
+
 void intel_mocs_init(struct intel_gt *gt)
 {
 	intel_mocs_init_l3cc_table(gt);
 
-	if (HAS_GLOBAL_MOCS_REGISTERS(gt->i915))
+	if (HAS_GLOBAL_MOCS_REGISTERS(gt->i915)) {
+		intel_read_clos_way_mask(gt);
 		intel_mocs_init_global(gt);
+	}
 }
diff --git a/drivers/gpu/drm/i915/gt/intel_mocs.h b/drivers/gpu/drm/i915/gt/intel_mocs.h
index 2ae816b7ca19..e64e1b104753 100644
--- a/drivers/gpu/drm/i915/gt/intel_mocs.h
+++ b/drivers/gpu/drm/i915/gt/intel_mocs.h
@@ -53,6 +53,7 @@ struct i915_request;
 struct intel_engine_cs;
 struct intel_gt;
 
+void intel_mocs_init_global(struct intel_gt *gt);
 void intel_mocs_init(struct intel_gt *gt);
 void intel_mocs_init_engine(struct intel_engine_cs *engine);
 
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index b42651a387d9..0e250416c5a9 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -1621,6 +1621,14 @@ struct drm_i915_private {
 		bool distrust_bios_wm;
 	} wm;
 
+	/* Last Level Cache  Class of Service */
+	struct {
+		bool support_way_mask_read;
+		atomic_t active_clos;
+#define NUM_OF_CLOS 4
+		u16 way_mask[NUM_OF_CLOS];
+	} clos;
+
 	struct dram_info {
 		bool valid;
 		bool is_16gb_dimm;
diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
index 02e1ef10c47e..399acb7a36d8 100644
--- a/drivers/gpu/drm/i915/i915_reg.h
+++ b/drivers/gpu/drm/i915/i915_reg.h
@@ -8845,6 +8845,7 @@ enum {
 #define   ICL_PCODE_MEM_SUBSYSYSTEM_INFO	0xd
 #define     ICL_PCODE_MEM_SS_READ_GLOBAL_INFO	(0x0 << 8)
 #define     ICL_PCODE_MEM_SS_READ_QGV_POINT_INFO(point)	(((point) << 16) | (0x1 << 8))
+#define   ICL_PCODE_LLC_COS_WAY_MASK_INFO	0x1d
 #define   GEN6_PCODE_READ_D_COMP		0x10
 #define   GEN6_PCODE_WRITE_D_COMP		0x11
 #define   HSW_PCODE_DE_WRITE_FREQ_REQ		0x17
diff --git a/drivers/gpu/drm/i915/i915_sysfs.c b/drivers/gpu/drm/i915/i915_sysfs.c
index d8a3b180c084..b53143416396 100644
--- a/drivers/gpu/drm/i915/i915_sysfs.c
+++ b/drivers/gpu/drm/i915/i915_sysfs.c
@@ -34,6 +34,7 @@
 #include "i915_sysfs.h"
 #include "intel_pm.h"
 #include "intel_sideband.h"
+#include "gt/intel_mocs.h"
 
 static inline struct drm_i915_private *kdev_minor_to_i915(struct device *kdev)
 {
@@ -257,6 +258,62 @@ static const struct bin_attribute dpf_attrs_1 = {
 	.private = (void *)1
 };
 
+static ssize_t closctrl_show(struct device *kdev,
+			     struct device_attribute *attr, char *buf)
+{
+	struct drm_i915_private *dev_priv = kdev_minor_to_i915(kdev);
+	ssize_t len = 0;
+	int i;
+
+	for (i = 0; i < NUM_OF_CLOS; i++) {
+		if (i == atomic_read(&dev_priv->clos.active_clos))
+			len += snprintf(buf + len, PAGE_SIZE, "%s0x%x%s ",
+					"[", dev_priv->clos.way_mask[i], "]");
+		else
+			len += snprintf(buf + len, PAGE_SIZE, "0x%x ",
+					dev_priv->clos.way_mask[i]);
+	}
+	len += snprintf(buf + len, PAGE_SIZE, "\n");
+
+	return len;
+}
+
+static ssize_t closctrl_store(struct device *kdev,
+			      struct device_attribute *attr,
+			      const char *buf, size_t count)
+{
+	struct drm_i915_private *dev_priv = kdev_minor_to_i915(kdev);
+	u8 active_clos, clos_index;
+	bool valid_mask = false;
+	ssize_t ret;
+	u16 way_mask;
+
+	ret = kstrtou16(buf, 0, &way_mask);
+	if (ret)
+		return ret;
+
+	active_clos = atomic_read(&dev_priv->clos.active_clos);
+
+	if (dev_priv->clos.way_mask[active_clos] == way_mask)
+		return count;
+
+	for (clos_index = 0; clos_index < NUM_OF_CLOS; clos_index++) {
+		if (dev_priv->clos.way_mask[clos_index] == way_mask) {
+			atomic_set(&dev_priv->clos.active_clos, clos_index);
+			valid_mask = true;
+			break;
+		}
+	}
+
+	if (!valid_mask)
+		return -EINVAL;
+
+	intel_mocs_init_global(&dev_priv->gt);
+
+	return count;
+}
+static DEVICE_ATTR_RW(closctrl);
+
 static ssize_t gt_act_freq_mhz_show(struct device *kdev,
 				    struct device_attribute *attr, char *buf)
 {
@@ -576,6 +633,13 @@ void i915_setup_sysfs(struct drm_i915_private *dev_priv)
 	struct device *kdev = dev_priv->drm.primary->kdev;
 	int ret;
 
+	if (dev_priv->clos.support_way_mask_read) {
+		ret = sysfs_create_file(&kdev->kobj,
+					&dev_attr_closctrl.attr);
+		if (ret)
+			DRM_ERROR("LLC COS sysfs setup failed\n");
+	}
+
 #ifdef CONFIG_PM
 	if (HAS_RC6(dev_priv)) {
 		ret = sysfs_merge_group(&kdev->kobj,
@@ -626,6 +690,9 @@ void i915_teardown_sysfs(struct drm_i915_private *dev_priv)
 
 	i915_teardown_error_capture(kdev);
 
+	if (dev_priv->clos.support_way_mask_read)
+		sysfs_remove_file(&kdev->kobj, &dev_attr_closctrl.attr);
+
 	if (IS_VALLEYVIEW(dev_priv) || IS_CHERRYVIEW(dev_priv))
 		sysfs_remove_files(&kdev->kobj, vlv_attrs);
 	else
-- 
2.20.1

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