dma-buf: Add an API for importing sync files (v10)

This patch is analogous to the previous sync file export patch in that
it allows you to import a sync_file into a dma-buf. Unlike the previous
patch, however, this does add genuinely new functionality to dma-buf.
Without this, the only way to attach a sync_file to a dma-buf is to
submit a batch to your driver of choice which waits on the sync_file and
claims to write to the dma-buf. Even if said batch is a no-op, a submit
is typically way more overhead than just attaching a fence. A submit
may also imply extra synchronization with other work because it happens
on a hardware queue.

In the Vulkan world, this is useful for dealing with the out-fence from
vkQueuePresent. Current Linux window-systems (X11, Wayland, etc.) all
rely on dma-buf implicit sync. Since Vulkan is an explicit sync API, we
get a set of fences (VkSemaphores) in vkQueuePresent and have to stash
those as an exclusive (write) fence on the dma-buf. We handle it in
Mesa today with the above mentioned dummy submit trick. This ioctl
would allow us to set it directly without the dummy submit.

This may also open up possibilities for GPU drivers to move away from
implicit sync for their kernel driver uAPI and instead provide sync
files and rely on dma-buf import/export for communicating with other
implicit sync clients.

We make the explicit choice here to only allow setting RW fences which
translates to an exclusive fence on the dma_resv. There's no use for
read-only fences for communicating with other implicit sync userspace
and any such attempts are likely to be racy at best. When we got to
insert the RW fence, the actual fence we set as the new exclusive fence
is a combination of the sync_file provided by the user and all the other
fences on the dma_resv. This ensures that the newly added exclusive
fence will never signal before the old one would have and ensures that
we don't break any dma_resv contracts. We require userspace to specify
RW in the flags for symmetry with the export ioctl and in case we ever
want to support read fences in the future.

There is one downside here that's worth documenting: If two clients
writing to the same dma-buf using this API race with each other, their
actions on the dma-buf may happen in parallel or in an undefined order.
Both with and without this API, the pattern is the same: Collect all
the fences on dma-buf, submit work which depends on said fences, and
then set a new exclusive (write) fence on the dma-buf which depends on
said work. The difference is that, when it's all handled by the GPU
driver's submit ioctl, the three operations happen atomically under the
dma_resv lock. If two userspace submits race, one will happen before
the other. You aren't guaranteed which but you are guaranteed that
they're strictly ordered. If userspace manages the fences itself, then
these three operations happen separately and the two render operations
may happen genuinely in parallel or get interleaved. However, this is a
case of userspace racing with itself. As long as we ensure userspace
can't back the kernel into a corner, it should be fine.

v2 (Jason Ekstrand):
- Use a wrapper dma_fence_array of all fences including the new one
when importing an exclusive fence.

v3 (Jason Ekstrand):
- Lock around setting shared fences as well as exclusive
- Mark SIGNAL_SYNC_FILE as a read-write ioctl.
- Initialize ret to 0 in dma_buf_wait_sync_file

v4 (Jason Ekstrand):
- Use the new dma_resv_get_singleton helper

v5 (Jason Ekstrand):
- Rename the IOCTLs to import/export rather than wait/signal
- Drop the WRITE flag and always get/set the exclusive fence

v6 (Jason Ekstrand):
- Split import and export into separate patches
- New commit message

v7 (Daniel Vetter):
- Fix the uapi header to use the right struct in the ioctl
- Use a separate dma_buf_import_sync_file struct
- Add kerneldoc for dma_buf_import_sync_file

v8 (Jason Ekstrand):
- Rebase on Christian König's fence rework

v9 (Daniel Vetter):
- Fix -EINVAL checks for the flags parameter
- Add documentation about read/write fences
- Add documentation about the expected usage of import/export and
specifically call out the possible userspace race.

v10 (Simon Ser):
- Fix a typo in the docs

Signed-off-by: Jason Ekstrand <jason@jlekstrand.net>
Signed-off-by: Jason Ekstrand <jason.ekstrand@intel.com>
Signed-off-by: Jason Ekstrand <jason.ekstrand@collabora.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: Simon Ser <contact@emersion.fr>
Link: https://patchwork.freedesktop.org/patch/msgid/20220608152142.14495-3-jason@jlekstrand.net

dma-buf: Add an API for exporting sync files (v14)

Modern userspace APIs like Vulkan are built on an explicit
synchronization model. This doesn't always play nicely with the
implicit synchronization used in the kernel and assumed by X11 and
Wayland. The client -> compositor half of the synchronization isn't too
bad, at least on intel, because we can control whether or not i915
synchronizes on the buffer and whether or not it's considered written.

The harder part is the compositor -> client synchronization when we get
the buffer back from the compositor. We're required to be able to
provide the client with a VkSemaphore and VkFence representing the point
in time where the window system (compositor and/or display) finished
using the buffer. With current APIs, it's very hard to do this in such
a way that we don't get confused by the Vulkan driver's access of the
buffer. In particular, once we tell the kernel that we're rendering to
the buffer again, any CPU waits on the buffer or GPU dependencies will
wait on some of the client rendering and not just the compositor.

This new IOCTL solves this problem by allowing us to get a snapshot of
the implicit synchronization state of a given dma-buf in the form of a
sync file. It's effectively the same as a poll() or I915_GEM_WAIT only,
instead of CPU waiting directly, it encapsulates the wait operation, at
the current moment in time, in a sync_file so we can check/wait on it
later. As long as the Vulkan driver does the sync_file export from the
dma-buf before we re-introduce it for rendering, it will only contain
fences from the compositor or display. This allows to accurately turn
it into a VkFence or VkSemaphore without any over-synchronization.

By making this an ioctl on the dma-buf itself, it allows this new
functionality to be used in an entirely driver-agnostic way without
having access to a DRM fd. This makes it ideal for use in driver-generic
code in Mesa or in a client such as a compositor where the DRM fd may be
hard to reach.

v2 (Jason Ekstrand):
- Use a wrapper dma_fence_array of all fences including the new one
when importing an exclusive fence.

v3 (Jason Ekstrand):
- Lock around setting shared fences as well as exclusive
- Mark SIGNAL_SYNC_FILE as a read-write ioctl.
- Initialize ret to 0 in dma_buf_wait_sync_file

v4 (Jason Ekstrand):
- Use the new dma_resv_get_singleton helper

v5 (Jason Ekstrand):
- Rename the IOCTLs to import/export rather than wait/signal
- Drop the WRITE flag and always get/set the exclusive fence

v6 (Jason Ekstrand):
- Drop the sync_file import as it was all-around sketchy and not nearly
as useful as import.
- Re-introduce READ/WRITE flag support for export
- Rework the commit message

v7 (Jason Ekstrand):
- Require at least one sync flag
- Fix a refcounting bug: dma_resv_get_excl() doesn't take a reference
- Use _rcu helpers since we're accessing the dma_resv read-only

v8 (Jason Ekstrand):
- Return -ENOMEM if the sync_file_create fails
- Predicate support on IS_ENABLED(CONFIG_SYNC_FILE)

v9 (Jason Ekstrand):
- Add documentation for the new ioctl

v10 (Jason Ekstrand):
- Go back to dma_buf_sync_file as the ioctl struct name

v11 (Daniel Vetter):
- Go back to dma_buf_export_sync_file as the ioctl struct name
- Better kerneldoc describing what the read/write flags do

v12 (Christian König):
- Document why we chose to make it an ioctl on dma-buf

v13 (Jason Ekstrand):
- Rebase on Christian König's fence rework

v14 (Daniel Vetter & Christian König):
- Use dma_rev_usage_rw to get the properly inverted usage to pass to
dma_resv_get_singleton()
- Clean up the sync_file and fd if copy_to_user() fails

Signed-off-by: Jason Ekstrand <jason@jlekstrand.net>
Signed-off-by: Jason Ekstrand <jason.ekstrand@intel.com>
Signed-off-by: Jason Ekstrand <jason.ekstrand@collabora.com>
Acked-by: Simon Ser <contact@emersion.fr>
Reviewed-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: Simon Ser <contact@emersion.fr>
Link: https://patchwork.freedesktop.org/patch/msgid/20220608152142.14495-2-jason@jlekstrand.net

dma-buf: fix use of DMA_BUF_SET_NAME_{A,B} in userspace

The typedefs u32 and u64 are not available in userspace. Thus user get
an error he try to use DMA_BUF_SET_NAME_A or DMA_BUF_SET_NAME_B:

$ gcc -Wall -c -MMD -c -o ioctls_list.o ioctls_list.c
In file included from /usr/include/x86_64-linux-gnu/asm/ioctl.h:1,
from /usr/include/linux/ioctl.h:5,
from /usr/include/asm-generic/ioctls.h:5,
from ioctls_list.c:11:
ioctls_list.c:463:29: error: ‘u32’ undeclared here (not in a function)
463 | { "DMA_BUF_SET_NAME_A", DMA_BUF_SET_NAME_A, -1, -1 }, // linux/dma-buf.h
| ^~~~~~~~~~~~~~~~~~
ioctls_list.c:464:29: error: ‘u64’ undeclared here (not in a function)
464 | { "DMA_BUF_SET_NAME_B", DMA_BUF_SET_NAME_B, -1, -1 }, // linux/dma-buf.h
| ^~~~~~~~~~~~~~~~~~

The issue was initially reported here[1].

[1]: https://github.com/jerome-pouiller/ioctl/pull/14

Signed-off-by: Jérôme Pouiller <jerome.pouiller@silabs.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Fixes: a5bff92eaac4 ("dma-buf: Fix SET_NAME ioctl uapi")
CC: stable@vger.kernel.org
Link: https://patchwork.freedesktop.org/patch/msgid/20220517072708.245265-1-Jerome.Pouiller@silabs.com
Signed-off-by: Christian König <christian.koenig@amd.com>

dma-buf: Document DMA_BUF_IOCTL_SYNC (v3)

This adds a new "DMA Buffer ioctls" section to the dma-buf docs and adds
documentation for DMA_BUF_IOCTL_SYNC.

v2 (Daniel Vetter):
- Fix a couple typos
- Add commentary about synchronization with other devices
- Use item list format for describing flags

v3 (Pekka Paalanen):
- Clarify stalling requirements.
- Be more clear that that DMA_BUF_IOCTL_SYNC with SINC_END has to be
called before more GPU work happens.

Signed-off-by: Jason Ekstrand <jason@jlekstrand.net>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Acked-by: Christian König <christian.koenig@amd.com>
Acked-by: Pekka Paalanen <pekka.paalanen@collabora.com>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20210617194258.579011-1-jason@jlekstrand.net

dma-buf: Fix SET_NAME ioctl uapi

The uapi is the same on 32 and 64 bit, but the number isn't. Everyone
who botched this please re-read:

https://www.kernel.org/doc/html/v5.4-preprc-cpu/ioctl/botching-up-ioctls.html

Also, the type argument for the ioctl macros is for the type the void
__user *arg pointer points at, which in this case would be the
variable-sized char[] of a 0 terminated string. So this was botched in
more than just the usual ways.

Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: Chenbo Feng <fengc@google.com>
Cc: Greg Hackmann <ghackmann@google.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: linux-media@vger.kernel.org
Cc: linaro-mm-sig@lists.linaro.org
Cc: minchan@kernel.org
Cc: surenb@google.com
Cc: jenhaochen@google.com
Cc: Martin Liu <liumartin@google.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Tested-by: Martin Liu <liumartin@google.com>
Reviewed-by: Martin Liu <liumartin@google.com>
Signed-off-by: Sumit Semwal <sumit.semwal@linaro.org>
[sumits: updated some checkpatch fixes, corrected author email]
Link: https://patchwork.freedesktop.org/patch/msgid/20200407133002.3486387-1-daniel.vetter@ffwll.ch

dma-buf: add DMA_BUF_SET_NAME ioctls

This patch adds complimentary DMA_BUF_SET_NAME ioctls, which lets
userspace processes attach a free-form name to each buffer.

This information can be extremely helpful for tracking and accounting
shared buffers. For example, on Android, we know what each buffer will
be used for at allocation time: GL, multimedia, camera, etc. The
userspace allocator can use DMA_BUF_SET_NAME to associate that
information with the buffer, so we can later give developers a
breakdown of how much memory they're allocating for graphics, camera,
etc.

Signed-off-by: Greg Hackmann <ghackmann@google.com>
Signed-off-by: Chenbo Feng <fengc@google.com>
Signed-off-by: Sumit Semwal <sumit.semwal@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20190613223408.139221-3-fengc@google.com

License cleanup: add SPDX license identifier to uapi header files with a license

Many user space API headers have licensing information, which is either
incomplete, badly formatted or just a shorthand for referring to the
license under which the file is supposed to be. This makes it hard for
compliance tools to determine the correct license.

Update these files with an SPDX license identifier. The identifier was
chosen based on the license information in the file.

GPL/LGPL licensed headers get the matching GPL/LGPL SPDX license
identifier with the added 'WITH Linux-syscall-note' exception, which is
the officially assigned exception identifier for the kernel syscall
exception:

NOTE! This copyright does *not* cover user programs that use kernel
services by normal system calls - this is merely considered normal use
of the kernel, and does *not* fall under the heading of "derived work".

This exception makes it possible to include GPL headers into non GPL
code, without confusing license compliance tools.

Headers which have either explicit dual licensing or are just licensed
under a non GPL license are updated with the corresponding SPDX
identifier and the GPLv2 with syscall exception identifier. The format
is:
((GPL-2.0 WITH Linux-syscall-note) OR SPDX-ID-OF-OTHER-LICENSE)

SPDX license identifiers are a legally binding shorthand, which can be
used instead of the full boiler plate text. The update does not remove
existing license information as this has to be done on a case by case
basis and the copyright holders might have to be consulted. This will
happen in a separate step.

This patch is based on work done by Thomas Gleixner and Kate Stewart and
Philippe Ombredanne. See the previous patch in this series for the
methodology of how this patch was researched.

Reviewed-by: Kate Stewart <kstewart@linuxfoundation.org>
Reviewed-by: Philippe Ombredanne <pombredanne@nexb.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

dma-buf: Add ioctls to allow userspace to flush

The userspace might need some sort of cache coherency management e.g. when CPU
and GPU domains are being accessed through dma-buf at the same time. To
circumvent this problem there are begin/end coherency markers, that forward
directly to existing dma-buf device drivers vfunc hooks. Userspace can make use
of those markers through the DMA_BUF_IOCTL_SYNC ioctl. The sequence would be
used like following:
- mmap dma-buf fd
- for each drawing/upload cycle in CPU 1. SYNC_START ioctl, 2. read/write
to mmap area 3. SYNC_END ioctl. This can be repeated as often as you
want (with the new data being consumed by the GPU or say scanout device)
- munmap once you don't need the buffer any more

v2 (Tiago): Fix header file type names (u64 -> __u64)
v3 (Tiago): Add documentation. Use enum dma_buf_sync_flags to the begin/end
dma-buf functions. Check for overflows in start/length.
v4 (Tiago): use 2d regions for sync.
v5 (Tiago): forget about 2d regions (v4); use _IOW in DMA_BUF_IOCTL_SYNC and
remove range information from struct dma_buf_sync.
v6 (Tiago): use __u64 structured padded flags instead enum. Adjust
documentation about the recommendation on using sync ioctls.
v7 (Tiago): Alex' nit on flags definition and being even more wording in the
doc about sync usage.
v9 (Tiago): remove useless is_dma_buf_file check. Fix sync.flags conditionals
and its mask order check. Add <linux/types.h> include in dma-buf.h.

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: David Herrmann <dh.herrmann@gmail.com>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Reviewed-by: Stéphane Marchesin <marcheu@chromium.org>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Signed-off-by: Tiago Vignatti <tiago.vignatti@intel.com>
Reviewed-by: David Herrmann <dh.herrmann@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1455228291-29640-1-git-send-email-tiago.vignatti@intel.com