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![Christian König](/assets/img/avatar_default.png)
So far we had the approach of using a directed acyclic graph with the dma_resv obj. This turned out to have many downsides, especially it means that every single driver and user of this interface needs to be aware of this restriction when adding fences. If the rules for the DAG are not followed then we end up with potential hard to debug memory corruption, information leaks or even elephant big security holes because we allow userspace to access freed up memory. Since we already took a step back from that by always looking at all fences we now go a step further and stop dropping the shared fences when a new exclusive one is added. v2: Drop some now superflous documentation v3: Add some more documentation for the new handling. Signed-off-by: Christian König <christian.koenig@amd.com> Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch> Link: https://patchwork.freedesktop.org/patch/msgid/20220321135856.1331-11-christian.koenig@amd.com
446 lines
15 KiB
C
446 lines
15 KiB
C
/*
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* Header file for reservations for dma-buf and ttm
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*
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* Copyright(C) 2011 Linaro Limited. All rights reserved.
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* Copyright (C) 2012-2013 Canonical Ltd
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* Copyright (C) 2012 Texas Instruments
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*
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* Authors:
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* Rob Clark <robdclark@gmail.com>
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* Maarten Lankhorst <maarten.lankhorst@canonical.com>
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* Thomas Hellstrom <thellstrom-at-vmware-dot-com>
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*
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* Based on bo.c which bears the following copyright notice,
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* but is dual licensed:
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*
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* Copyright (c) 2006-2009 VMware, Inc., Palo Alto, CA., USA
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* All Rights Reserved.
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*
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* Permission is hereby granted, free of charge, to any person obtaining a
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* copy of this software and associated documentation files (the
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* "Software"), to deal in the Software without restriction, including
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* without limitation the rights to use, copy, modify, merge, publish,
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* distribute, sub license, and/or sell copies of the Software, and to
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* permit persons to whom the Software is furnished to do so, subject to
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* the following conditions:
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*
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* The above copyright notice and this permission notice (including the
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* next paragraph) shall be included in all copies or substantial portions
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* of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NON-INFRINGEMENT. IN NO EVENT SHALL
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* THE COPYRIGHT HOLDERS, AUTHORS AND/OR ITS SUPPLIERS BE LIABLE FOR ANY CLAIM,
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* DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
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* OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE
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* USE OR OTHER DEALINGS IN THE SOFTWARE.
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*/
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#ifndef _LINUX_RESERVATION_H
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#define _LINUX_RESERVATION_H
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#include <linux/ww_mutex.h>
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#include <linux/dma-fence.h>
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#include <linux/slab.h>
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#include <linux/seqlock.h>
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#include <linux/rcupdate.h>
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extern struct ww_class reservation_ww_class;
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struct dma_resv_list;
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/**
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* struct dma_resv - a reservation object manages fences for a buffer
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*
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* There are multiple uses for this, with sometimes slightly different rules in
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* how the fence slots are used.
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*
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* One use is to synchronize cross-driver access to a struct dma_buf, either for
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* dynamic buffer management or just to handle implicit synchronization between
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* different users of the buffer in userspace. See &dma_buf.resv for a more
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* in-depth discussion.
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*
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* The other major use is to manage access and locking within a driver in a
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* buffer based memory manager. struct ttm_buffer_object is the canonical
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* example here, since this is where reservation objects originated from. But
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* use in drivers is spreading and some drivers also manage struct
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* drm_gem_object with the same scheme.
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*/
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struct dma_resv {
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/**
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* @lock:
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*
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* Update side lock. Don't use directly, instead use the wrapper
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* functions like dma_resv_lock() and dma_resv_unlock().
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*
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* Drivers which use the reservation object to manage memory dynamically
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* also use this lock to protect buffer object state like placement,
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* allocation policies or throughout command submission.
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*/
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struct ww_mutex lock;
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/**
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* @seq:
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*
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* Sequence count for managing RCU read-side synchronization, allows
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* read-only access to @fence_excl and @fence while ensuring we take a
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* consistent snapshot.
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*/
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seqcount_ww_mutex_t seq;
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/**
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* @fence_excl:
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*
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* The exclusive fence, if there is one currently.
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*
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* To guarantee that no fences are lost, this new fence must signal
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* only after the previous exclusive fence has signalled. If
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* semantically only a new access is added without actually treating the
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* previous one as a dependency the exclusive fences can be strung
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* together using struct dma_fence_chain.
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*
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* Note that actual semantics of what an exclusive or shared fence mean
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* is defined by the user, for reservation objects shared across drivers
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* see &dma_buf.resv.
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*/
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struct dma_fence __rcu *fence_excl;
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/**
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* @fence:
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*
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* List of current shared fences.
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*
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* There are no ordering constraints of shared fences against the
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* exclusive fence slot. If a waiter needs to wait for all access, it
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* has to wait for both sets of fences to signal.
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*
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* A new fence is added by calling dma_resv_add_shared_fence(). Since
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* this often needs to be done past the point of no return in command
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* submission it cannot fail, and therefore sufficient slots need to be
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* reserved by calling dma_resv_reserve_shared().
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*
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* Note that actual semantics of what an exclusive or shared fence mean
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* is defined by the user, for reservation objects shared across drivers
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* see &dma_buf.resv.
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*/
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struct dma_resv_list __rcu *fence;
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};
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/**
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* struct dma_resv_iter - current position into the dma_resv fences
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*
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* Don't touch this directly in the driver, use the accessor function instead.
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*
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* IMPORTANT
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*
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* When using the lockless iterators like dma_resv_iter_next_unlocked() or
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* dma_resv_for_each_fence_unlocked() beware that the iterator can be restarted.
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* Code which accumulates statistics or similar needs to check for this with
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* dma_resv_iter_is_restarted().
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*/
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struct dma_resv_iter {
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/** @obj: The dma_resv object we iterate over */
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struct dma_resv *obj;
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/** @all_fences: If all fences should be returned */
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bool all_fences;
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/** @fence: the currently handled fence */
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struct dma_fence *fence;
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/** @seq: sequence number to check for modifications */
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unsigned int seq;
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/** @index: index into the shared fences */
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unsigned int index;
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/** @fences: the shared fences; private, *MUST* not dereference */
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struct dma_resv_list *fences;
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/** @shared_count: number of shared fences */
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unsigned int shared_count;
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/** @is_restarted: true if this is the first returned fence */
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bool is_restarted;
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};
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struct dma_fence *dma_resv_iter_first_unlocked(struct dma_resv_iter *cursor);
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struct dma_fence *dma_resv_iter_next_unlocked(struct dma_resv_iter *cursor);
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struct dma_fence *dma_resv_iter_first(struct dma_resv_iter *cursor);
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struct dma_fence *dma_resv_iter_next(struct dma_resv_iter *cursor);
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/**
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* dma_resv_iter_begin - initialize a dma_resv_iter object
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* @cursor: The dma_resv_iter object to initialize
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* @obj: The dma_resv object which we want to iterate over
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* @all_fences: If all fences should be returned or just the exclusive one
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*/
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static inline void dma_resv_iter_begin(struct dma_resv_iter *cursor,
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struct dma_resv *obj,
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bool all_fences)
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{
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cursor->obj = obj;
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cursor->all_fences = all_fences;
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cursor->fence = NULL;
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}
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/**
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* dma_resv_iter_end - cleanup a dma_resv_iter object
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* @cursor: the dma_resv_iter object which should be cleaned up
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*
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* Make sure that the reference to the fence in the cursor is properly
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* dropped.
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*/
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static inline void dma_resv_iter_end(struct dma_resv_iter *cursor)
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{
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dma_fence_put(cursor->fence);
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}
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/**
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* dma_resv_iter_is_exclusive - test if the current fence is the exclusive one
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* @cursor: the cursor of the current position
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*
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* Returns true if the currently returned fence is the exclusive one.
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*/
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static inline bool dma_resv_iter_is_exclusive(struct dma_resv_iter *cursor)
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{
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return cursor->index == 0;
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}
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/**
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* dma_resv_iter_is_restarted - test if this is the first fence after a restart
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* @cursor: the cursor with the current position
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*
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* Return true if this is the first fence in an iteration after a restart.
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*/
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static inline bool dma_resv_iter_is_restarted(struct dma_resv_iter *cursor)
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{
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return cursor->is_restarted;
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}
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/**
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* dma_resv_for_each_fence_unlocked - unlocked fence iterator
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* @cursor: a struct dma_resv_iter pointer
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* @fence: the current fence
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*
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* Iterate over the fences in a struct dma_resv object without holding the
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* &dma_resv.lock and using RCU instead. The cursor needs to be initialized
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* with dma_resv_iter_begin() and cleaned up with dma_resv_iter_end(). Inside
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* the iterator a reference to the dma_fence is held and the RCU lock dropped.
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*
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* Beware that the iterator can be restarted when the struct dma_resv for
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* @cursor is modified. Code which accumulates statistics or similar needs to
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* check for this with dma_resv_iter_is_restarted(). For this reason prefer the
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* lock iterator dma_resv_for_each_fence() whenever possible.
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*/
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#define dma_resv_for_each_fence_unlocked(cursor, fence) \
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for (fence = dma_resv_iter_first_unlocked(cursor); \
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fence; fence = dma_resv_iter_next_unlocked(cursor))
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/**
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* dma_resv_for_each_fence - fence iterator
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* @cursor: a struct dma_resv_iter pointer
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* @obj: a dma_resv object pointer
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* @all_fences: true if all fences should be returned
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* @fence: the current fence
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*
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* Iterate over the fences in a struct dma_resv object while holding the
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* &dma_resv.lock. @all_fences controls if the shared fences are returned as
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* well. The cursor initialisation is part of the iterator and the fence stays
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* valid as long as the lock is held and so no extra reference to the fence is
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* taken.
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*/
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#define dma_resv_for_each_fence(cursor, obj, all_fences, fence) \
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for (dma_resv_iter_begin(cursor, obj, all_fences), \
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fence = dma_resv_iter_first(cursor); fence; \
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fence = dma_resv_iter_next(cursor))
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#define dma_resv_held(obj) lockdep_is_held(&(obj)->lock.base)
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#define dma_resv_assert_held(obj) lockdep_assert_held(&(obj)->lock.base)
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#ifdef CONFIG_DEBUG_MUTEXES
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void dma_resv_reset_shared_max(struct dma_resv *obj);
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#else
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static inline void dma_resv_reset_shared_max(struct dma_resv *obj) {}
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#endif
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/**
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* dma_resv_lock - lock the reservation object
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* @obj: the reservation object
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* @ctx: the locking context
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*
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* Locks the reservation object for exclusive access and modification. Note,
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* that the lock is only against other writers, readers will run concurrently
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* with a writer under RCU. The seqlock is used to notify readers if they
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* overlap with a writer.
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*
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* As the reservation object may be locked by multiple parties in an
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* undefined order, a #ww_acquire_ctx is passed to unwind if a cycle
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* is detected. See ww_mutex_lock() and ww_acquire_init(). A reservation
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* object may be locked by itself by passing NULL as @ctx.
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*
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* When a die situation is indicated by returning -EDEADLK all locks held by
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* @ctx must be unlocked and then dma_resv_lock_slow() called on @obj.
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*
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* Unlocked by calling dma_resv_unlock().
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*
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* See also dma_resv_lock_interruptible() for the interruptible variant.
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*/
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static inline int dma_resv_lock(struct dma_resv *obj,
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struct ww_acquire_ctx *ctx)
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{
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return ww_mutex_lock(&obj->lock, ctx);
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}
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/**
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* dma_resv_lock_interruptible - lock the reservation object
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* @obj: the reservation object
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* @ctx: the locking context
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*
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* Locks the reservation object interruptible for exclusive access and
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* modification. Note, that the lock is only against other writers, readers
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* will run concurrently with a writer under RCU. The seqlock is used to
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* notify readers if they overlap with a writer.
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*
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* As the reservation object may be locked by multiple parties in an
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* undefined order, a #ww_acquire_ctx is passed to unwind if a cycle
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* is detected. See ww_mutex_lock() and ww_acquire_init(). A reservation
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* object may be locked by itself by passing NULL as @ctx.
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*
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* When a die situation is indicated by returning -EDEADLK all locks held by
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* @ctx must be unlocked and then dma_resv_lock_slow_interruptible() called on
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* @obj.
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*
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* Unlocked by calling dma_resv_unlock().
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*/
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static inline int dma_resv_lock_interruptible(struct dma_resv *obj,
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struct ww_acquire_ctx *ctx)
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{
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return ww_mutex_lock_interruptible(&obj->lock, ctx);
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}
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/**
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* dma_resv_lock_slow - slowpath lock the reservation object
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* @obj: the reservation object
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* @ctx: the locking context
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*
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* Acquires the reservation object after a die case. This function
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* will sleep until the lock becomes available. See dma_resv_lock() as
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* well.
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*
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* See also dma_resv_lock_slow_interruptible() for the interruptible variant.
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*/
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static inline void dma_resv_lock_slow(struct dma_resv *obj,
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struct ww_acquire_ctx *ctx)
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{
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ww_mutex_lock_slow(&obj->lock, ctx);
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}
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/**
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* dma_resv_lock_slow_interruptible - slowpath lock the reservation
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* object, interruptible
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* @obj: the reservation object
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* @ctx: the locking context
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*
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* Acquires the reservation object interruptible after a die case. This function
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* will sleep until the lock becomes available. See
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* dma_resv_lock_interruptible() as well.
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*/
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static inline int dma_resv_lock_slow_interruptible(struct dma_resv *obj,
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struct ww_acquire_ctx *ctx)
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{
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return ww_mutex_lock_slow_interruptible(&obj->lock, ctx);
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}
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/**
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* dma_resv_trylock - trylock the reservation object
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* @obj: the reservation object
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*
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* Tries to lock the reservation object for exclusive access and modification.
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* Note, that the lock is only against other writers, readers will run
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* concurrently with a writer under RCU. The seqlock is used to notify readers
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* if they overlap with a writer.
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*
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* Also note that since no context is provided, no deadlock protection is
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* possible, which is also not needed for a trylock.
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*
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* Returns true if the lock was acquired, false otherwise.
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*/
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static inline bool __must_check dma_resv_trylock(struct dma_resv *obj)
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{
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return ww_mutex_trylock(&obj->lock, NULL);
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}
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/**
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* dma_resv_is_locked - is the reservation object locked
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* @obj: the reservation object
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*
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* Returns true if the mutex is locked, false if unlocked.
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*/
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static inline bool dma_resv_is_locked(struct dma_resv *obj)
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{
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return ww_mutex_is_locked(&obj->lock);
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}
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/**
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* dma_resv_locking_ctx - returns the context used to lock the object
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* @obj: the reservation object
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*
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* Returns the context used to lock a reservation object or NULL if no context
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* was used or the object is not locked at all.
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*
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* WARNING: This interface is pretty horrible, but TTM needs it because it
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* doesn't pass the struct ww_acquire_ctx around in some very long callchains.
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* Everyone else just uses it to check whether they're holding a reservation or
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* not.
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*/
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static inline struct ww_acquire_ctx *dma_resv_locking_ctx(struct dma_resv *obj)
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{
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return READ_ONCE(obj->lock.ctx);
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}
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/**
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* dma_resv_unlock - unlock the reservation object
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* @obj: the reservation object
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*
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* Unlocks the reservation object following exclusive access.
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*/
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static inline void dma_resv_unlock(struct dma_resv *obj)
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{
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dma_resv_reset_shared_max(obj);
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ww_mutex_unlock(&obj->lock);
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}
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/**
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* dma_resv_excl_fence - return the object's exclusive fence
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* @obj: the reservation object
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*
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* Returns the exclusive fence (if any). Caller must either hold the objects
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* through dma_resv_lock() or the RCU read side lock through rcu_read_lock(),
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* or one of the variants of each
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*
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* RETURNS
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* The exclusive fence or NULL
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*/
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static inline struct dma_fence *
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dma_resv_excl_fence(struct dma_resv *obj)
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{
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return rcu_dereference_check(obj->fence_excl, dma_resv_held(obj));
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}
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void dma_resv_init(struct dma_resv *obj);
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void dma_resv_fini(struct dma_resv *obj);
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int dma_resv_reserve_shared(struct dma_resv *obj, unsigned int num_fences);
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void dma_resv_add_shared_fence(struct dma_resv *obj, struct dma_fence *fence);
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void dma_resv_replace_fences(struct dma_resv *obj, uint64_t context,
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struct dma_fence *fence);
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void dma_resv_add_excl_fence(struct dma_resv *obj, struct dma_fence *fence);
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int dma_resv_get_fences(struct dma_resv *obj, bool write,
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unsigned int *num_fences, struct dma_fence ***fences);
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int dma_resv_copy_fences(struct dma_resv *dst, struct dma_resv *src);
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long dma_resv_wait_timeout(struct dma_resv *obj, bool wait_all, bool intr,
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unsigned long timeout);
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bool dma_resv_test_signaled(struct dma_resv *obj, bool test_all);
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void dma_resv_describe(struct dma_resv *obj, struct seq_file *seq);
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#endif /* _LINUX_RESERVATION_H */
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