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drm/i915: Allow the sysadmin to override security mitigations
The clear-residuals mitigation 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.
To disable just the clear-residuals mitigation (on Ivybridge, Baytrail,
or Haswell) use the module parameter: i915.mitigations=auto,!residuals
Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/1858
Fixes: 47f8253d2b
("drm/i915/gen7: Clear all EU/L3 residual contexts")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Jon Bloomfield <jon.bloomfield@intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: stable@vger.kernel.org # v5.7
Reviewed-by: Jon Bloomfield <jon.bloomfield@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210111225220.3483-3-chris@chris-wilson.co.uk
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@ -38,6 +38,7 @@ i915-y += i915_drv.o \
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i915_config.o \
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i915_irq.o \
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i915_getparam.o \
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i915_mitigations.o \
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i915_params.o \
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i915_pci.o \
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i915_scatterlist.o \
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@ -32,6 +32,7 @@
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#include "gen6_ppgtt.h"
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#include "gen7_renderclear.h"
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#include "i915_drv.h"
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#include "i915_mitigations.h"
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#include "intel_breadcrumbs.h"
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#include "intel_context.h"
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#include "intel_gt.h"
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@ -918,7 +919,8 @@ static int switch_context(struct i915_request *rq)
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GEM_BUG_ON(HAS_EXECLISTS(engine->i915));
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if (engine->wa_ctx.vma && ce != engine->kernel_context) {
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if (engine->wa_ctx.vma->private != ce) {
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if (engine->wa_ctx.vma->private != ce &&
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i915_mitigate_clear_residuals()) {
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ret = clear_residuals(rq);
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if (ret)
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return ret;
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146
drivers/gpu/drm/i915/i915_mitigations.c
Normal file
146
drivers/gpu/drm/i915/i915_mitigations.c
Normal file
@ -0,0 +1,146 @@
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// SPDX-License-Identifier: MIT
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/*
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* Copyright © 2021 Intel Corporation
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*/
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#include <linux/kernel.h>
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#include <linux/moduleparam.h>
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#include <linux/slab.h>
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#include <linux/string.h>
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#include "i915_drv.h"
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#include "i915_mitigations.h"
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static unsigned long mitigations __read_mostly = ~0UL;
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enum {
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CLEAR_RESIDUALS = 0,
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};
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static const char * const names[] = {
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[CLEAR_RESIDUALS] = "residuals",
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};
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bool i915_mitigate_clear_residuals(void)
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{
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return READ_ONCE(mitigations) & BIT(CLEAR_RESIDUALS);
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}
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static int mitigations_set(const char *val, const struct kernel_param *kp)
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{
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unsigned long new = ~0UL;
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char *str, *sep, *tok;
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bool first = true;
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int err = 0;
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BUILD_BUG_ON(ARRAY_SIZE(names) >= BITS_PER_TYPE(mitigations));
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str = kstrdup(val, GFP_KERNEL);
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if (!str)
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return -ENOMEM;
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for (sep = str; (tok = strsep(&sep, ","));) {
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bool enable = true;
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int i;
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/* Be tolerant of leading/trailing whitespace */
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tok = strim(tok);
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if (first) {
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first = false;
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if (!strcmp(tok, "auto"))
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continue;
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new = 0;
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if (!strcmp(tok, "off"))
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continue;
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}
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if (*tok == '!') {
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enable = !enable;
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tok++;
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}
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if (!strncmp(tok, "no", 2)) {
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enable = !enable;
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tok += 2;
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}
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if (*tok == '\0')
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continue;
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for (i = 0; i < ARRAY_SIZE(names); i++) {
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if (!strcmp(tok, names[i])) {
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if (enable)
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new |= BIT(i);
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else
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new &= ~BIT(i);
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break;
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}
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}
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if (i == ARRAY_SIZE(names)) {
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pr_err("Bad \"%s.mitigations=%s\", '%s' is unknown\n",
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DRIVER_NAME, val, tok);
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err = -EINVAL;
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break;
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}
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}
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kfree(str);
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if (err)
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return err;
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WRITE_ONCE(mitigations, new);
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return 0;
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}
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static int mitigations_get(char *buffer, const struct kernel_param *kp)
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{
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unsigned long local = READ_ONCE(mitigations);
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int count, i;
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bool enable;
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if (!local)
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return scnprintf(buffer, PAGE_SIZE, "%s\n", "off");
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if (local & BIT(BITS_PER_LONG - 1)) {
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count = scnprintf(buffer, PAGE_SIZE, "%s,", "auto");
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enable = false;
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} else {
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enable = true;
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count = 0;
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}
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for (i = 0; i < ARRAY_SIZE(names); i++) {
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if ((local & BIT(i)) != enable)
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continue;
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count += scnprintf(buffer + count, PAGE_SIZE - count,
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"%s%s,", enable ? "" : "!", names[i]);
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}
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buffer[count - 1] = '\n';
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return count;
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}
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static const struct kernel_param_ops ops = {
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.set = mitigations_set,
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.get = mitigations_get,
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};
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module_param_cb_unsafe(mitigations, &ops, NULL, 0600);
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MODULE_PARM_DESC(mitigations,
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"Selectively enable security mitigations for all Intel® GPUs in the system.\n"
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"\n"
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" auto -- enables all mitigations required for the platform [default]\n"
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" off -- disables all mitigations\n"
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"\n"
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"Individual mitigations can be enabled by passing a comma-separated string,\n"
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"e.g. mitigations=residuals to enable only clearing residuals or\n"
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"mitigations=auto,noresiduals to disable only the clear residual mitigation.\n"
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"Either '!' or 'no' may be used to switch from enabling the mitigation to\n"
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"disabling it.\n"
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"\n"
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"Active mitigations for Ivybridge, Baytrail, Haswell:\n"
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" residuals -- clear all thread-local registers between contexts"
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);
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13
drivers/gpu/drm/i915/i915_mitigations.h
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13
drivers/gpu/drm/i915/i915_mitigations.h
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@ -0,0 +1,13 @@
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/* SPDX-License-Identifier: MIT */
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/*
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* Copyright © 2021 Intel Corporation
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*/
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#ifndef __I915_MITIGATIONS_H__
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#define __I915_MITIGATIONS_H__
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#include <linux/types.h>
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bool i915_mitigate_clear_residuals(void);
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#endif /* __I915_MITIGATIONS_H__ */
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