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9d1305ef80
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>
Link: https://patchwork.freedesktop.org/patch/msgid/20190322092325.5883-1-chris@chris-wilson.co.uk
62 lines
1.1 KiB
C
62 lines
1.1 KiB
C
/*
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* SPDX-License-Identifier: MIT
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*
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* Copyright © 2018 Intel Corporation
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*/
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#include <linux/nospec.h>
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#include <linux/sched/signal.h>
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#include <linux/uaccess.h>
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#include <uapi/drm/i915_drm.h>
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#include "i915_user_extensions.h"
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#include "i915_utils.h"
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int i915_user_extensions(struct i915_user_extension __user *ext,
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const i915_user_extension_fn *tbl,
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unsigned int count,
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void *data)
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{
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unsigned int stackdepth = 512;
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while (ext) {
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int i, err;
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u32 name;
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u64 next;
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if (!stackdepth--) /* recursion vs useful flexibility */
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return -E2BIG;
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err = check_user_mbz(&ext->flags);
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if (err)
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return err;
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for (i = 0; i < ARRAY_SIZE(ext->rsvd); i++) {
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err = check_user_mbz(&ext->rsvd[i]);
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if (err)
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return err;
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}
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if (get_user(name, &ext->name))
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return -EFAULT;
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err = -EINVAL;
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if (name < count) {
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name = array_index_nospec(name, count);
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if (tbl[name])
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err = tbl[name](ext, data);
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}
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if (err)
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return err;
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if (get_user(next, &ext->next_extension) ||
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overflows_type(next, ext))
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return -EFAULT;
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ext = u64_to_user_ptr(next);
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}
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return 0;
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}
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