drm/i915: Remove redundant user_access_end() from __copy_from_user() error path

Objtool reports:

  drivers/gpu/drm/i915/gem/i915_gem_execbuffer.o: warning: objtool: .altinstr_replacement+0x36: redundant UACCESS disable

__copy_from_user() already does both STAC and CLAC, so the
user_access_end() in its error path adds an extra unnecessary CLAC.

Fixes: 0b2c8f8b ("i915: fix missing user_access_end() in page fault exception case")
Reported-by: Thomas Gleixner <tglx@linutronix.de>
Reported-by: Sedat Dilek <sedat.dilek@gmail.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Nick Desaulniers <ndesaulniers@google.com>
Tested-by: Sedat Dilek <sedat.dilek@gmail.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://github.com/ClangBuiltLinux/linux/issues/617
Link: https://lkml.kernel.org/r/51a4155c5bc2ca847a9cbe85c1c11918bb193141.1564086017.git.jpoimboe@redhat.com

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

@@ -1628,6 +1628,7 @@ static int check_relocations(const struct drm_i915_gem_exec_object2 *entry)
 
 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;
@@ -1635,7 +1636,6 @@ static int eb_copy_relocations(const struct i915_execbuffer *eb)
 	for (i = 0; i < count; i++) {
 		const unsigned int nreloc = eb->exec[i].relocation_count;
 		struct drm_i915_gem_relocation_entry __user *urelocs;
-		struct drm_i915_gem_relocation_entry *relocs;
 		unsigned long size;
 		unsigned long copied;
 
@@ -1663,14 +1663,8 @@ static int eb_copy_relocations(const struct i915_execbuffer *eb)
 
 			if (__copy_from_user((char *)relocs + copied,
 					     (char __user *)urelocs + copied,
-					     len)) {
-end_user:
-				user_access_end();
-end:
-				kvfree(relocs);
-				err = -EFAULT;
-				goto err;
-			}
+					     len))
+				goto end;
 
 			copied += len;
 		} while (copied < size);
@@ -1699,10 +1693,14 @@ static int eb_copy_relocations(const struct i915_execbuffer *eb)
 
 	return 0;
 
+end_user:
+	user_access_end();
+end:
+	kvfree(relocs);
+	err = -EFAULT;
 err:
 	while (i--) {
-		struct drm_i915_gem_relocation_entry *relocs =
-			u64_to_ptr(typeof(*relocs), eb->exec[i].relocs_ptr);
+		relocs = u64_to_ptr(typeof(*relocs), eb->exec[i].relocs_ptr);
 		if (eb->exec[i].relocation_count)
 			kvfree(relocs);
 	}