From 9d1305ef80b95dde0337106ed8b826604e2155ad Mon Sep 17 00:00:00 2001 From: Chris Wilson Date: Fri, 22 Mar 2019 09:23:22 +0000 Subject: drm/i915: Introduce the i915_user_extension_method 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 Cc: Tvrtko Ursulin Cc: Joonas Lahtinen Reviewed-by: Tvrtko Ursulin Link: https://patchwork.freedesktop.org/patch/msgid/20190322092325.5883-1-chris@chris-wilson.co.uk --- drivers/gpu/drm/i915/i915_user_extensions.c | 61 +++++++++++++++++++++++++++++ 1 file changed, 61 insertions(+) create mode 100644 drivers/gpu/drm/i915/i915_user_extensions.c (limited to 'drivers/gpu/drm/i915/i915_user_extensions.c') diff --git a/drivers/gpu/drm/i915/i915_user_extensions.c b/drivers/gpu/drm/i915/i915_user_extensions.c new file mode 100644 index 000000000000..c822d0aafd2d --- /dev/null +++ b/drivers/gpu/drm/i915/i915_user_extensions.c @@ -0,0 +1,61 @@ +/* + * SPDX-License-Identifier: MIT + * + * Copyright © 2018 Intel Corporation + */ + +#include +#include +#include + +#include + +#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; +} -- cgit v1.2.3