drm/i915/userptr: Never allow userptr into the mappable GGTT

Daniel Vetter uncovered a nasty cycle in using the mmu-notifiers to
invalidate userptr objects which also happen to be pulled into GGTT
mmaps. That is when we unbind the userptr object (on mmu invalidation),
we revoke all CPU mmaps, which may then recurse into mmu invalidation.

We looked for ways of breaking the cycle, but the revocation on
invalidation is required and cannot be avoided. The only solution we
could see was to not allow such GGTT bindings of userptr objects in the
first place. In practice, no one really wants to use a GGTT mmapping of
a CPU pointer...

Just before Daniel's explosive lockdep patches land in v5.4-rc1, we got
a genuine blip from CI:

<4>[  246.793958] ======================================================
<4>[  246.793972] WARNING: possible circular locking dependency detected
<4>[  246.793989] 5.3.0-gbd6c56f50d15-drmtip_372+ #1 Tainted: G     U
<4>[  246.794003] ------------------------------------------------------
<4>[  246.794017] kswapd0/145 is trying to acquire lock:
<4>[  246.794030] 000000003f565be6 (&dev->struct_mutex/1){+.+.}, at: userptr_mn_invalidate_range_start+0x18f/0x220 [i915]
<4>[  246.794250]
                  but task is already holding lock:
<4>[  246.794263] 000000001799cef9 (&anon_vma->rwsem){++++}, at: page_lock_anon_vma_read+0xe6/0x2a0
<4>[  246.794291]
                  which lock already depends on the new lock.

<4>[  246.794307]
                  the existing dependency chain (in reverse order) is:
<4>[  246.794322]
                  -> #3 (&anon_vma->rwsem){++++}:
<4>[  246.794344]        down_write+0x33/0x70
<4>[  246.794357]        __vma_adjust+0x3d9/0x7b0
<4>[  246.794370]        __split_vma+0x16a/0x180
<4>[  246.794385]        mprotect_fixup+0x2a5/0x320
<4>[  246.794399]        do_mprotect_pkey+0x208/0x2e0
<4>[  246.794413]        __x64_sys_mprotect+0x16/0x20
<4>[  246.794429]        do_syscall_64+0x55/0x1c0
<4>[  246.794443]        entry_SYSCALL_64_after_hwframe+0x49/0xbe
<4>[  246.794456]
                  -> #2 (&mapping->i_mmap_rwsem){++++}:
<4>[  246.794478]        down_write+0x33/0x70
<4>[  246.794493]        unmap_mapping_pages+0x48/0x130
<4>[  246.794519]        i915_vma_revoke_mmap+0x81/0x1b0 [i915]
<4>[  246.794519]        i915_vma_unbind+0x11d/0x4a0 [i915]
<4>[  246.794519]        i915_vma_destroy+0x31/0x300 [i915]
<4>[  246.794519]        __i915_gem_free_objects+0xb8/0x4b0 [i915]
<4>[  246.794519]        drm_file_free.part.0+0x1e6/0x290
<4>[  246.794519]        drm_release+0xa6/0xe0
<4>[  246.794519]        __fput+0xc2/0x250
<4>[  246.794519]        task_work_run+0x82/0xb0
<4>[  246.794519]        do_exit+0x35b/0xdb0
<4>[  246.794519]        do_group_exit+0x34/0xb0
<4>[  246.794519]        __x64_sys_exit_group+0xf/0x10
<4>[  246.794519]        do_syscall_64+0x55/0x1c0
<4>[  246.794519]        entry_SYSCALL_64_after_hwframe+0x49/0xbe
<4>[  246.794519]
                  -> #1 (&vm->mutex){+.+.}:
<4>[  246.794519]        i915_gem_shrinker_taints_mutex+0x6d/0xe0 [i915]
<4>[  246.794519]        i915_address_space_init+0x9f/0x160 [i915]
<4>[  246.794519]        i915_ggtt_init_hw+0x55/0x170 [i915]
<4>[  246.794519]        i915_driver_probe+0xc9f/0x1620 [i915]
<4>[  246.794519]        i915_pci_probe+0x43/0x1b0 [i915]
<4>[  246.794519]        pci_device_probe+0x9e/0x120
<4>[  246.794519]        really_probe+0xea/0x3d0
<4>[  246.794519]        driver_probe_device+0x10b/0x120
<4>[  246.794519]        device_driver_attach+0x4a/0x50
<4>[  246.794519]        __driver_attach+0x97/0x130
<4>[  246.794519]        bus_for_each_dev+0x74/0xc0
<4>[  246.794519]        bus_add_driver+0x13f/0x210
<4>[  246.794519]        driver_register+0x56/0xe0
<4>[  246.794519]        do_one_initcall+0x58/0x300
<4>[  246.794519]        do_init_module+0x56/0x1f6
<4>[  246.794519]        load_module+0x25bd/0x2a40
<4>[  246.794519]        __se_sys_finit_module+0xd3/0xf0
<4>[  246.794519]        do_syscall_64+0x55/0x1c0
<4>[  246.794519]        entry_SYSCALL_64_after_hwframe+0x49/0xbe
<4>[  246.794519]
                  -> #0 (&dev->struct_mutex/1){+.+.}:
<4>[  246.794519]        __lock_acquire+0x15d8/0x1e90
<4>[  246.794519]        lock_acquire+0xa6/0x1c0
<4>[  246.794519]        __mutex_lock+0x9d/0x9b0
<4>[  246.794519]        userptr_mn_invalidate_range_start+0x18f/0x220 [i915]
<4>[  246.794519]        __mmu_notifier_invalidate_range_start+0x85/0x110
<4>[  246.794519]        try_to_unmap_one+0x76b/0x860
<4>[  246.794519]        rmap_walk_anon+0x104/0x280
<4>[  246.794519]        try_to_unmap+0xc0/0xf0
<4>[  246.794519]        shrink_page_list+0x561/0xc10
<4>[  246.794519]        shrink_inactive_list+0x220/0x440
<4>[  246.794519]        shrink_node_memcg+0x36e/0x740
<4>[  246.794519]        shrink_node+0xcb/0x490
<4>[  246.794519]        balance_pgdat+0x241/0x580
<4>[  246.794519]        kswapd+0x16c/0x530
<4>[  246.794519]        kthread+0x119/0x130
<4>[  246.794519]        ret_from_fork+0x24/0x50
<4>[  246.794519]
                  other info that might help us debug this:

<4>[  246.794519] Chain exists of:
                    &dev->struct_mutex/1 --> &mapping->i_mmap_rwsem --> &anon_vma->rwsem

<4>[  246.794519]  Possible unsafe locking scenario:

<4>[  246.794519]        CPU0                    CPU1
<4>[  246.794519]        ----                    ----
<4>[  246.794519]   lock(&anon_vma->rwsem);
<4>[  246.794519]                                lock(&mapping->i_mmap_rwsem);
<4>[  246.794519]                                lock(&anon_vma->rwsem);
<4>[  246.794519]   lock(&dev->struct_mutex/1);
<4>[  246.794519]
                   *** DEADLOCK ***

v2: Say no to mmap_ioctl

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=111744
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=111870Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: stable@vger.kernel.org
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190928082546.3473-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/gem/i915_gem_mman.c

@@ -343,6 +343,7 @@ vm_fault_t i915_gem_fault(struct vm_fault *vmf)
 		/* fallthrough */
 	case -EIO: /* shmemfs failure from swap device */
 	case -EFAULT: /* purged object */
+	case -ENODEV: /* bad object, how did you get here! */
 		return VM_FAULT_SIGBUS;
 
 	case -ENOSPC: /* shmemfs allocation failure */
@@ -466,10 +467,16 @@ i915_gem_mmap_gtt(struct drm_file *file,
 	if (!obj)
 		return -ENOENT;
 
+	if (i915_gem_object_never_bind_ggtt(obj)) {
+		ret = -ENODEV;
+		goto out;
+	}
+
 	ret = create_mmap_offset(obj);
 	if (ret == 0)
 		*offset = drm_vma_node_offset_addr(&obj->base.vma_node);
 
+out:
 	i915_gem_object_put(obj);
 	return ret;
 }

drivers/gpu/drm/i915/gem/i915_gem_object.h

@@ -152,6 +152,12 @@ i915_gem_object_is_proxy(const struct drm_i915_gem_object *obj)
 	return obj->ops->flags & I915_GEM_OBJECT_IS_PROXY;
 }
 
+static inline bool
+i915_gem_object_never_bind_ggtt(const struct drm_i915_gem_object *obj)
+{
+	return obj->ops->flags & I915_GEM_OBJECT_NO_GGTT;
+}
+
 static inline bool
 i915_gem_object_needs_async_cancel(const struct drm_i915_gem_object *obj)
 {

drivers/gpu/drm/i915/gem/i915_gem_object_types.h

@@ -32,7 +32,8 @@ struct drm_i915_gem_object_ops {
 #define I915_GEM_OBJECT_HAS_STRUCT_PAGE	BIT(0)
 #define I915_GEM_OBJECT_IS_SHRINKABLE	BIT(1)
 #define I915_GEM_OBJECT_IS_PROXY	BIT(2)
-#define I915_GEM_OBJECT_ASYNC_CANCEL	BIT(3)
+#define I915_GEM_OBJECT_NO_GGTT		BIT(3)
+#define I915_GEM_OBJECT_ASYNC_CANCEL	BIT(4)
 
 	/* Interface between the GEM object and its backing storage.
 	 * get_pages() is called once prior to the use of the associated set

drivers/gpu/drm/i915/gem/i915_gem_userptr.c

@@ -710,6 +710,7 @@ i915_gem_userptr_dmabuf_export(struct drm_i915_gem_object *obj)
 static const struct drm_i915_gem_object_ops i915_gem_userptr_ops = {
 	.flags = I915_GEM_OBJECT_HAS_STRUCT_PAGE |
 		 I915_GEM_OBJECT_IS_SHRINKABLE |
+		 I915_GEM_OBJECT_NO_GGTT |
 		 I915_GEM_OBJECT_ASYNC_CANCEL,
 	.get_pages = i915_gem_userptr_get_pages,
 	.put_pages = i915_gem_userptr_put_pages,

drivers/gpu/drm/i915/i915_gem.c

@@ -970,6 +970,9 @@ i915_gem_object_ggtt_pin(struct drm_i915_gem_object *obj,
 
 	lockdep_assert_held(&obj->base.dev->struct_mutex);
 
+	if (i915_gem_object_never_bind_ggtt(obj))
+		return ERR_PTR(-ENODEV);
+
 	if (flags & PIN_MAPPABLE &&
 	    (!view || view->type == I915_GGTT_VIEW_NORMAL)) {
 		/* If the required space is larger than the available