[PATCH 3/3] drm/i915: Allow the sysadmin to override security mitigations
Chris Wilson
chris at chris-wilson.co.uk
Sat Jan 9 21:54:12 UTC 2021
The clear-residuals mitigate is a relatively heavy hammer and under some
circumstances the user may wish to forgo the context isolation in order
to meet some performance requirement. Introduce a generic module
parameter to allow selectively enabling/disabling different mitigations.
Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/1858
Fixes: 47f8253d2b89 ("drm/i915/gen7: Clear all EU/L3 residual contexts")
Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
Cc: Jon Bloomfield <jon.bloomfield at intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi at intel.com>
Cc: stable at vger.kernel.org # v5.7
---
drivers/gpu/drm/i915/Makefile | 1 +
.../gpu/drm/i915/gt/intel_ring_submission.c | 4 +-
drivers/gpu/drm/i915/i915_mitigations.c | 149 ++++++++++++++++++
drivers/gpu/drm/i915/i915_mitigations.h | 13 ++
4 files changed, 166 insertions(+), 1 deletion(-)
create mode 100644 drivers/gpu/drm/i915/i915_mitigations.c
create mode 100644 drivers/gpu/drm/i915/i915_mitigations.h
diff --git a/drivers/gpu/drm/i915/Makefile b/drivers/gpu/drm/i915/Makefile
index 4074d8cb0d6e..48f82c354611 100644
--- a/drivers/gpu/drm/i915/Makefile
+++ b/drivers/gpu/drm/i915/Makefile
@@ -38,6 +38,7 @@ i915-y += i915_drv.o \
i915_config.o \
i915_irq.o \
i915_getparam.o \
+ i915_mitigations.o \
i915_params.o \
i915_pci.o \
i915_scatterlist.o \
diff --git a/drivers/gpu/drm/i915/gt/intel_ring_submission.c b/drivers/gpu/drm/i915/gt/intel_ring_submission.c
index 724d56c9583d..657afd8ebc14 100644
--- a/drivers/gpu/drm/i915/gt/intel_ring_submission.c
+++ b/drivers/gpu/drm/i915/gt/intel_ring_submission.c
@@ -32,6 +32,7 @@
#include "gen6_ppgtt.h"
#include "gen7_renderclear.h"
#include "i915_drv.h"
+#include "i915_mitigations.h"
#include "intel_breadcrumbs.h"
#include "intel_context.h"
#include "intel_gt.h"
@@ -918,7 +919,8 @@ static int switch_context(struct i915_request *rq)
GEM_BUG_ON(HAS_EXECLISTS(engine->i915));
if (engine->wa_ctx.vma && ce != engine->kernel_context) {
- if (engine->wa_ctx.vma->private != ce) {
+ if (engine->wa_ctx.vma->private != ce &&
+ i915_mitigate_clear_residuals()) {
ret = clear_residuals(rq);
if (ret)
return ret;
diff --git a/drivers/gpu/drm/i915/i915_mitigations.c b/drivers/gpu/drm/i915/i915_mitigations.c
new file mode 100644
index 000000000000..0c2d83cb5bfa
--- /dev/null
+++ b/drivers/gpu/drm/i915/i915_mitigations.c
@@ -0,0 +1,149 @@
+// SPDX-License-Identifier: MIT
+/*
+ * Copyright © 2021 Intel Corporation
+ */
+
+#include <linux/kernel.h>
+#include <linux/moduleparam.h>
+#include <linux/slab.h>
+#include <linux/string.h>
+
+#include "i915_mitigations.h"
+
+static unsigned long mitigations = ~0UL;
+
+enum {
+ CLEAR_RESIDUALS = 0,
+};
+
+static const char *names[] = {
+ [CLEAR_RESIDUALS] = "residuals",
+};
+
+bool i915_mitigate_clear_residuals(void)
+{
+ return READ_ONCE(mitigations) & BIT(CLEAR_RESIDUALS);
+}
+
+static int mitigations_set(const char *val, const struct kernel_param *kp)
+{
+ unsigned long new = ~0UL;
+ char *str, *sep, *tok;
+ bool first = true;
+ int err = 0;
+
+ str = kstrdup(val, GFP_KERNEL);
+ if (!str)
+ return -ENOMEM;
+
+ for (sep = str; (tok = strsep(&sep, ","));) {
+ bool enable = true;
+ int i;
+
+ /* Be tolerant of leading/trailing whitespace */
+ tok = strim(tok);
+
+ if (first) {
+ first = false;
+
+ if (!strcmp(tok, "auto")) {
+ new = ~0UL;
+ continue;
+ }
+
+ new = 0;
+ if (!strcmp(tok, "off"))
+ continue;
+ }
+
+ if (*tok == '!') {
+ enable = !enable;
+ tok++;
+ }
+
+ if (!strncmp(tok, "no", 2)) {
+ enable = !enable;
+ tok += 2;
+ }
+
+ if (*tok == '\0')
+ continue;
+
+ for (i = 0; i < ARRAY_SIZE(names); i++) {
+ if (!strcmp(tok, names[i])) {
+ if (enable)
+ new |= BIT(i);
+ else
+ new &= ~BIT(i);
+ break;
+ }
+ }
+ if (i == ARRAY_SIZE(names)) {
+ pr_err("Unrecognised i915.mitigation name '%s'\n", tok);
+ err = -EINVAL;
+ break;
+ }
+ }
+ kfree(str);
+ if (err)
+ return err;
+
+ WRITE_ONCE(mitigations, new);
+ return 0;
+}
+
+static int mitigations_get(char *buffer, const struct kernel_param *kp)
+{
+ unsigned long local = READ_ONCE(mitigations);
+ int count, i;
+
+ if (!local)
+ return scnprintf(buffer, PAGE_SIZE, "%s\n", "off");
+
+ if (local & BIT(BITS_PER_LONG - 1)) {
+ count = scnprintf(buffer, PAGE_SIZE, "%s,", "auto");
+
+ for (i = 0; i < ARRAY_SIZE(names); i++) {
+ if (local & BIT(i))
+ continue;
+
+ count += scnprintf(buffer + count, PAGE_SIZE - count,
+ "!%s,", names[i]);
+ }
+ } else {
+ count = 0;
+
+ for (i = 0; i < ARRAY_SIZE(names); i++) {
+ if (!(local & BIT(i)))
+ continue;
+
+ count += scnprintf(buffer + count, PAGE_SIZE - count,
+ "%s,", names[i]);
+ }
+ }
+
+ buffer[count - 1] = '\n';
+ return count;
+}
+
+static const struct kernel_param_ops ops = {
+ .set = mitigations_set,
+ .get = mitigations_get,
+};
+
+module_param_cb_unsafe(mitigations, &ops, NULL, 0600);
+MODULE_PARM_DESC(mitigations,
+"Selectively enable security mitigations for all Intel® GPUs in the system.\n"
+"\n"
+" auto -- enables all mitigations required for the platform [default]\n"
+" off -- disables all mitigations\n"
+"\n"
+"Individual mitigations can be enabled by passing a comma-separated string,\n"
+"e.g. mitigations=residuals to enable only clearing residuals or\n"
+"mitigations=auto,noresiduals to disable only the clear residual mitigation.\n"
+"Either '!' or 'no' may be used to switch from enabling the mitigation to\n"
+"disabling it.\n"
+"\n"
+"Active mitigations for Ivybridge, Baytrail, Haswell:\n"
+" residuals -- clear all thread-local registers between contexts"
+);
diff --git a/drivers/gpu/drm/i915/i915_mitigations.h b/drivers/gpu/drm/i915/i915_mitigations.h
new file mode 100644
index 000000000000..1359d8135287
--- /dev/null
+++ b/drivers/gpu/drm/i915/i915_mitigations.h
@@ -0,0 +1,13 @@
+/* SPDX-License-Identifier: MIT */
+/*
+ * Copyright © 2021 Intel Corporation
+ */
+
+#ifndef __I915_MITIGATIONS_H__
+#define __I915_MITIGATIONS_H__
+
+#include <linux/types.h>
+
+bool i915_mitigate_clear_residuals(void);
+
+#endif /* __I915_MITIGATIONS_H__ */
--
2.20.1
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