@@ -46,6 +46,7 @@ i915-y := i915_drv.o \
i915_sw_fence.o \
i915_syncmap.o \
i915_sysfs.o \
+ i915_user_extensions.o \
intel_csr.o \
intel_device_info.o \
intel_pm.o \
new file mode 100644
@@ -0,0 +1,61 @@
+/*
+ * SPDX-License-Identifier: MIT
+ *
+ * Copyright © 2018 Intel Corporation
+ */
+
+#include <linux/nospec.h>
+#include <linux/sched/signal.h>
+#include <linux/uaccess.h>
+
+#include <uapi/drm/i915_drm.h>
+
+#include "i915_user_extensions.h"
+#include "i915_utils.h"
+
+int i915_user_extensions(struct i915_user_extension __user *ext,
+ const i915_user_extension_fn *tbl,
+ unsigned int count,
+ void *data)
+{
+ unsigned int stackdepth = 512;
+
+ while (ext) {
+ int i, err;
+ u32 name;
+ u64 next;
+
+ if (!stackdepth--) /* recursion vs useful flexibility */
+ return -E2BIG;
+
+ err = check_user_mbz(&ext->flags);
+ if (err)
+ return err;
+
+ for (i = 0; i < ARRAY_SIZE(ext->rsvd); i++) {
+ err = check_user_mbz(&ext->rsvd[i]);
+ if (err)
+ return err;
+ }
+
+ if (get_user(name, &ext->name))
+ return -EFAULT;
+
+ err = -EINVAL;
+ if (name < count) {
+ name = array_index_nospec(name, count);
+ if (tbl[name])
+ err = tbl[name](ext, data);
+ }
+ if (err)
+ return err;
+
+ if (get_user(next, &ext->next_extension) ||
+ overflows_type(next, ext))
+ return -EFAULT;
+
+ ext = u64_to_user_ptr(next);
+ }
+
+ return 0;
+}
new file mode 100644
@@ -0,0 +1,20 @@
+/*
+ * SPDX-License-Identifier: MIT
+ *
+ * Copyright © 2018 Intel Corporation
+ */
+
+#ifndef I915_USER_EXTENSIONS_H
+#define I915_USER_EXTENSIONS_H
+
+struct i915_user_extension;
+
+typedef int (*i915_user_extension_fn)(struct i915_user_extension __user *ext,
+ void *data);
+
+int i915_user_extensions(struct i915_user_extension __user *ext,
+ const i915_user_extension_fn *tbl,
+ unsigned int count,
+ void *data);
+
+#endif /* I915_USER_EXTENSIONS_H */
@@ -105,6 +105,37 @@
__T; \
})
+/*
+ * container_of_user: Extract the superclass from a pointer to a member.
+ *
+ * Exactly like container_of() with the exception that it plays nicely
+ * with sparse for __user @ptr.
+ */
+#define container_of_user(ptr, type, member) ({ \
+ void __user *__mptr = (void __user *)(ptr); \
+ BUILD_BUG_ON_MSG(!__same_type(*(ptr), ((type *)0)->member) && \
+ !__same_type(*(ptr), void), \
+ "pointer type mismatch in container_of()"); \
+ ((type __user *)(__mptr - offsetof(type, member))); })
+
+/*
+ * check_user_mbz: Check that a user value exists and is zero
+ *
+ * Frequently in our uABI we reserve space for future extensions, and
+ * two ensure that userspace is prepared we enforce that space must
+ * be zero. (Then any future extension can safely assume a default value
+ * of 0.)
+ *
+ * check_user_mbz() combines checking that the user pointer is accessible
+ * and that the contained value is zero.
+ *
+ * Returns: -EFAULT if not accessible, -EINVAL if !zero, or 0 on success.
+ */
+#define check_user_mbz(U) ({ \
+ typeof(*(U)) mbz__; \
+ get_user(mbz__, (U)) ? -EFAULT : mbz__ ? -EINVAL : 0; \
+})
+
static inline u64 ptr_to_u64(const void *ptr)
{
return (uintptr_t)ptr;
@@ -62,6 +62,28 @@ extern "C" {
#define I915_ERROR_UEVENT "ERROR"
#define I915_RESET_UEVENT "RESET"
+/*
+ * i915_user_extension: Base class for defining a chain of extensions
+ *
+ * Many interfaces need to grow over time. In most cases we can simply
+ * extend the struct and have userspace pass in more data. Another option,
+ * as demonstrated by Vulkan's approach to providing extensions for forward
+ * and backward compatibility, is to use a list of optional structs to
+ * provide those extra details.
+ *
+ * The key advantage to using an extension chain is that it allows us to
+ * redefine the interface more easily than an ever growing struct of
+ * increasing complexity, and for large parts of that interface to be
+ * entirely optional. The downside is more pointer chasing; chasing across
+ * the __user boundary with pointers encapsulated inside u64.
+ */
+struct i915_user_extension {
+ __u64 next_extension;
+ __u32 name;
+ __u32 flags; /* All undefined bits must be zero. */
+ __u32 rsvd[4]; /* Reserved for future use; must be zero. */
+};
+
/*
* MOCS indexes used for GPU surfaces, defining the cacheability of the
* surface data and the coherency for this data wrt. CPU vs. GPU accesses.
An idea for extending uABI inspired by Vulkan's extension chains. Instead of expanding the data struct for each ioctl every time we need to add a new feature, define an extension chain instead. As we add optional interfaces to control the ioctl, we define a new extension struct that can be linked into the ioctl data only when required by the user. The key advantage being able to ignore large control structs for optional interfaces/extensions, while being able to process them in a consistent manner. In comparison to other extensible ioctls, the key difference is the use of a linked chain of extension structs vs an array of tagged pointers. For example, struct drm_amdgpu_cs_chunk { __u32 chunk_id; __u32 length_dw; __u64 chunk_data; }; struct drm_amdgpu_cs_in { __u32 ctx_id; __u32 bo_list_handle; __u32 num_chunks; __u32 _pad; __u64 chunks; }; allows userspace to pass in array of pointers to extension structs, but must therefore keep constructing that array along side the command stream. In dynamic situations like that, a linked list is preferred and does not similar from extra cache line misses as the extension structs themselves must still be loaded separate to the chunks array. v2: Apply the tail call optimisation directly to nip the worry of stack overflow in the bud. v3: Defend against recursion. v4: Fixup local types to match new uabi Opens: - do we include the result as an out-field in each chain? struct i915_user_extension { __u64 next_extension; __u64 name; __s32 result; __u32 mbz; /* reserved for future use */ }; * Undecided, so provision some room for future expansion. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> --- drivers/gpu/drm/i915/Makefile | 1 + drivers/gpu/drm/i915/i915_user_extensions.c | 61 +++++++++++++++++++++ drivers/gpu/drm/i915/i915_user_extensions.h | 20 +++++++ drivers/gpu/drm/i915/i915_utils.h | 31 +++++++++++ include/uapi/drm/i915_drm.h | 22 ++++++++ 5 files changed, 135 insertions(+) create mode 100644 drivers/gpu/drm/i915/i915_user_extensions.c create mode 100644 drivers/gpu/drm/i915/i915_user_extensions.h