drm/i915/gem: Drop relocation slowpath

Since the relocations are no longer performed under a global
struct_mutex, or any other lock, that is also held by pagefault handlers,
we can relax and allow our fast path to take a fault. As we no longer
need to abort the fast path for lock avoidance, we no longer need the
slow path handling at all.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200311160310.26711-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c

@@ -1440,9 +1440,7 @@ static int eb_relocate_vma(struct i915_execbuffer *eb, struct eb_vma *ev)
 		 * we would try to acquire the struct mutex again. Obviously
 		 * this is bad and so lockdep complains vehemently.
 		 */
-		pagefault_disable();
-		copied = __copy_from_user_inatomic(r, urelocs, count * sizeof(r[0]));
-		pagefault_enable();
+		copied = __copy_from_user(r, urelocs, count * sizeof(r[0]));
 		if (unlikely(copied)) {
 			remain = -EFAULT;
 			goto out;
@@ -1492,236 +1490,6 @@ static int eb_relocate_vma(struct i915_execbuffer *eb, struct eb_vma *ev)
 	return remain;
 }
 
-static int
-eb_relocate_vma_slow(struct i915_execbuffer *eb, struct eb_vma *ev)
-{
-	const struct drm_i915_gem_exec_object2 *entry = ev->exec;
-	struct drm_i915_gem_relocation_entry *relocs =
-		u64_to_ptr(typeof(*relocs), entry->relocs_ptr);
-	unsigned int i;
-	int err;
-
-	for (i = 0; i < entry->relocation_count; i++) {
-		u64 offset = eb_relocate_entry(eb, ev, &relocs[i]);
-
-		if ((s64)offset < 0) {
-			err = (int)offset;
-			goto err;
-		}
-	}
-	err = 0;
-err:
-	reloc_cache_reset(&eb->reloc_cache);
-	return err;
-}
-
-static int check_relocations(const struct drm_i915_gem_exec_object2 *entry)
-{
-	const char __user *addr, *end;
-	unsigned long size;
-	char __maybe_unused c;
-
-	size = entry->relocation_count;
-	if (size == 0)
-		return 0;
-
-	if (size > N_RELOC(ULONG_MAX))
-		return -EINVAL;
-
-	addr = u64_to_user_ptr(entry->relocs_ptr);
-	size *= sizeof(struct drm_i915_gem_relocation_entry);
-	if (!access_ok(addr, size))
-		return -EFAULT;
-
-	end = addr + size;
-	for (; addr < end; addr += PAGE_SIZE) {
-		int err = __get_user(c, addr);
-		if (err)
-			return err;
-	}
-	return __get_user(c, end - 1);
-}
-
-static int eb_copy_relocations(const struct i915_execbuffer *eb)
-{
-	struct drm_i915_gem_relocation_entry *relocs;
-	const unsigned int count = eb->buffer_count;
-	unsigned int i;
-	int err;
-
-	for (i = 0; i < count; i++) {
-		const unsigned int nreloc = eb->exec[i].relocation_count;
-		struct drm_i915_gem_relocation_entry __user *urelocs;
-		unsigned long size;
-		unsigned long copied;
-
-		if (nreloc == 0)
-			continue;
-
-		err = check_relocations(&eb->exec[i]);
-		if (err)
-			goto err;
-
-		urelocs = u64_to_user_ptr(eb->exec[i].relocs_ptr);
-		size = nreloc * sizeof(*relocs);
-
-		relocs = kvmalloc_array(size, 1, GFP_KERNEL);
-		if (!relocs) {
-			err = -ENOMEM;
-			goto err;
-		}
-
-		/* copy_from_user is limited to < 4GiB */
-		copied = 0;
-		do {
-			unsigned int len =
-				min_t(u64, BIT_ULL(31), size - copied);
-
-			if (__copy_from_user((char *)relocs + copied,
-					     (char __user *)urelocs + copied,
-					     len))
-				goto end;
-
-			copied += len;
-		} while (copied < size);
-
-		/*
-		 * As we do not update the known relocation offsets after
-		 * relocating (due to the complexities in lock handling),
-		 * we need to mark them as invalid now so that we force the
-		 * relocation processing next time. Just in case the target
-		 * object is evicted and then rebound into its old
-		 * presumed_offset before the next execbuffer - if that
-		 * happened we would make the mistake of assuming that the
-		 * relocations were valid.
-		 */
-		if (!user_access_begin(urelocs, size))
-			goto end;
-
-		for (copied = 0; copied < nreloc; copied++)
-			unsafe_put_user(-1,
-					&urelocs[copied].presumed_offset,
-					end_user);
-		user_access_end();
-
-		eb->exec[i].relocs_ptr = (uintptr_t)relocs;
-	}
-
-	return 0;
-
-end_user:
-	user_access_end();
-end:
-	kvfree(relocs);
-	err = -EFAULT;
-err:
-	while (i--) {
-		relocs = u64_to_ptr(typeof(*relocs), eb->exec[i].relocs_ptr);
-		if (eb->exec[i].relocation_count)
-			kvfree(relocs);
-	}
-	return err;
-}
-
-static int eb_prefault_relocations(const struct i915_execbuffer *eb)
-{
-	const unsigned int count = eb->buffer_count;
-	unsigned int i;
-
-	for (i = 0; i < count; i++) {
-		int err;
-
-		err = check_relocations(&eb->exec[i]);
-		if (err)
-			return err;
-	}
-
-	return 0;
-}
-
-static noinline int eb_relocate_slow(struct i915_execbuffer *eb)
-{
-	bool have_copy = false;
-	struct eb_vma *ev;
-	int err = 0;
-
-repeat:
-	if (signal_pending(current)) {
-		err = -ERESTARTSYS;
-		goto out;
-	}
-
-	/*
-	 * We take 3 passes through the slowpatch.
-	 *
-	 * 1 - we try to just prefault all the user relocation entries and
-	 * then attempt to reuse the atomic pagefault disabled fast path again.
-	 *
-	 * 2 - we copy the user entries to a local buffer here outside of the
-	 * local and allow ourselves to wait upon any rendering before
-	 * relocations
-	 *
-	 * 3 - we already have a local copy of the relocation entries, but
-	 * were interrupted (EAGAIN) whilst waiting for the objects, try again.
-	 */
-	if (!err) {
-		err = eb_prefault_relocations(eb);
-	} else if (!have_copy) {
-		err = eb_copy_relocations(eb);
-		have_copy = err == 0;
-	} else {
-		cond_resched();
-		err = 0;
-	}
-	if (err)
-		goto out;
-
-	list_for_each_entry(ev, &eb->relocs, reloc_link) {
-		if (!have_copy) {
-			pagefault_disable();
-			err = eb_relocate_vma(eb, ev);
-			pagefault_enable();
-			if (err)
-				goto repeat;
-		} else {
-			err = eb_relocate_vma_slow(eb, ev);
-			if (err)
-				goto err;
-		}
-	}
-
-	/*
-	 * Leave the user relocations as are, this is the painfully slow path,
-	 * and we want to avoid the complication of dropping the lock whilst
-	 * having buffers reserved in the aperture and so causing spurious
-	 * ENOSPC for random operations.
-	 */
-
-err:
-	if (err == -EAGAIN)
-		goto repeat;
-
-out:
-	if (have_copy) {
-		const unsigned int count = eb->buffer_count;
-		unsigned int i;
-
-		for (i = 0; i < count; i++) {
-			const struct drm_i915_gem_exec_object2 *entry =
-				&eb->exec[i];
-			struct drm_i915_gem_relocation_entry *relocs;
-
-			if (!entry->relocation_count)
-				continue;
-
-			relocs = u64_to_ptr(typeof(*relocs), entry->relocs_ptr);
-			kvfree(relocs);
-		}
-	}
-
-	return err;
-}
-
 static int eb_relocate(struct i915_execbuffer *eb)
 {
 	int err;
@@ -1743,8 +1511,9 @@ static int eb_relocate(struct i915_execbuffer *eb)
 		struct eb_vma *ev;
 
 		list_for_each_entry(ev, &eb->relocs, reloc_link) {
-			if (eb_relocate_vma(eb, ev))
-				return eb_relocate_slow(eb);
+			err = eb_relocate_vma(eb, ev);
+			if (err)
+				return err;
 		}
 	}