Linaro-mm-sig October 2018

linaro-mm-sig@lists.linaro.org

1 participants
3 discussions

[PATCH v4 0/4] locking, drm: Fix ww mutex naming / algorithm inconsistency

by Thomas Hellstrom

This is a small fallout from a work to allow batching WW mutex locks and unlocks. Our Wound-Wait mutexes actually don't use the Wound-Wait algorithm but the Wait-Die algorithm. One could perhaps rename those mutexes tree-wide to "Wait-Die mutexes" or "Deadlock Avoidance mutexes". Another approach suggested here is to implement also the "Wound-Wait" algorithm as a per-WW-class choice, as it has advantages in some cases. See for example http://www.mathcs.emory.edu/~cheung/Courses/554/Syllabus/8-recv+serial/dead… Now Wound-Wait is a preemptive algorithm, and the preemption is implemented using a lazy scheme: If a wounded transaction is about to go to sleep on a contended WW mutex, we return -EDEADLK. That is sufficient for deadlock prevention. Since with WW mutexes we also require the aborted transaction to sleep waiting to lock the WW mutex it was aborted on, this choice also provides a suitable WW mutex to sleep on. If we were to return -EDEADLK on the first WW mutex lock after the transaction was wounded whether the WW mutex was contended or not, the transaction might frequently be restarted without a wait, which is far from optimal. Note also that with the lazy preemption scheme, contrary to Wait-Die there will be no rollbacks on lock contention of locks held by a transaction that has completed its locking sequence. The modeset locks are then changed from Wait-Die to Wound-Wait since the typical locking pattern of those locks very well matches the criterion for a substantial reduction in the number of rollbacks. For reservation objects, the benefit is more unclear at this point and they remain using Wait-Die. Cc: Ingo Molnar <mingo(a)redhat.com> Cc: Jonathan Corbet <corbet(a)lwn.net> Cc: Gustavo Padovan <gustavo(a)padovan.org> Cc: Maarten Lankhorst <maarten.lankhorst(a)linux.intel.com> Cc: Sean Paul <seanpaul(a)chromium.org> Cc: David Airlie <airlied(a)linux.ie> Cc: Davidlohr Bueso <dave(a)stgolabs.net> Cc: "Paul E. McKenney" <paulmck(a)linux.vnet.ibm.com> Cc: Josh Triplett <josh(a)joshtriplett.org> Cc: Thomas Gleixner <tglx(a)linutronix.de> Cc: Kate Stewart <kstewart(a)linuxfoundation.org> Cc: Philippe Ombredanne <pombredanne(a)nexb.com> Cc: Greg Kroah-Hartman <gregkh(a)linuxfoundation.org> Cc: linux-doc(a)vger.kernel.org Cc: linux-media(a)vger.kernel.org Cc: linaro-mm-sig(a)lists.linaro.org v2: Updated DEFINE_WW_CLASS() API, minor code- and comment fixes as detailed in each patch. v3: Included cleanup patch from Peter Zijlstra. Documentation fixes and a small correctness fix. v4: Reworked the correctness fix.

5 years, 11 months

[RFC] android: ion: How to properly clean caches for uncached allocations

by Liam Mark

The issue: Currently in ION if you allocate uncached memory it is possible that there are still dirty lines in the cache. And often these dirty lines in the cache are the zeros which were meant to clear out any sensitive kernel data. What this means is that if you allocate uncached memory from ION, and then subsequently write to that buffer (using the uncached mapping you are provided by ION) then the data you have written could be corrupted at some point in the future if a dirty line is evicted from the cache. Also this means there is a potential security issue. If an un-privileged userspace user allocated uncached memory (for example from the system heap) and then if they were to read from that buffer (through the un-cached mapping they are provided by ION), and if some of the zeros which were written to that memory are still in the cache then this un-privileged userspace user could read potentially sensitive kernel data. An unacceptable fix: I have included some sample code which should resolve this issue for the system heap and the cma heap on some architectures, however this code would not be acceptable for upstreaming since it uses hacks to clean the cache. Similar changes would need to be made to carveout heap and chunk heap. I would appreciate some feedback on the proper way for ION to clean the caches for memory it has allocated that is intended for uncached access. I realize that it may be tempting, as a solution to this problem, to simply strip uncached support from ION. I hope that we can try to find a solution which preserves uncached memory support as ION uncached memory is often used (though perhaps not in upstreamed code) in cases such as multimedia use cases where there is no CPU access required, in secure heap allocations, and in some cases where there is minimal CPU access and therefore uncached memory performs better. Signed-off-by: Liam Mark <lmark(a)codeaurora.org> --- drivers/staging/android/ion/ion.c | 16 ++++++++++++++++ drivers/staging/android/ion/ion.h | 5 ++++- drivers/staging/android/ion/ion_cma_heap.c | 3 +++ drivers/staging/android/ion/ion_page_pool.c | 8 ++++++-- drivers/staging/android/ion/ion_system_heap.c | 7 ++++++- 5 files changed, 35 insertions(+), 4 deletions(-) diff --git a/drivers/staging/android/ion/ion.c b/drivers/staging/android/ion/ion.c index 57e0d8035b2e..10e967b0a0f4 100644 --- a/drivers/staging/android/ion/ion.c +++ b/drivers/staging/android/ion/ion.c @@ -38,6 +38,22 @@ bool ion_buffer_cached(struct ion_buffer *buffer) return !!(buffer->flags & ION_FLAG_CACHED); } +void ion_pages_sync_for_device(struct page *page, size_t size, + enum dma_data_direction dir) +{ + struct scatterlist sg; + struct device dev = {0}; + + /* hack, use dummy device */ + arch_setup_dma_ops(&dev, 0, 0, NULL, false); + + sg_init_table(&sg, 1); + sg_set_page(&sg, page, size, 0); + /* hack, use phys address for dma address */ + sg_dma_address(&sg) = page_to_phys(page); + dma_sync_sg_for_device(&dev, &sg, 1, dir); +} + /* this function should only be called while dev->lock is held */ static void ion_buffer_add(struct ion_device *dev, struct ion_buffer *buffer) diff --git a/drivers/staging/android/ion/ion.h b/drivers/staging/android/ion/ion.h index a238f23c9116..227b9928d185 100644 --- a/drivers/staging/android/ion/ion.h +++ b/drivers/staging/android/ion/ion.h @@ -192,6 +192,9 @@ struct ion_heap { */ bool ion_buffer_cached(struct ion_buffer *buffer); +void ion_pages_sync_for_device(struct page *page, size_t size, + enum dma_data_direction dir); + /** * ion_buffer_fault_user_mappings - fault in user mappings of this buffer * @buffer: buffer @@ -333,7 +336,7 @@ struct ion_page_pool { struct ion_page_pool *ion_page_pool_create(gfp_t gfp_mask, unsigned int order, bool cached); void ion_page_pool_destroy(struct ion_page_pool *pool); -struct page *ion_page_pool_alloc(struct ion_page_pool *pool); +struct page *ion_page_pool_alloc(struct ion_page_pool *pool, bool *from_pool); void ion_page_pool_free(struct ion_page_pool *pool, struct page *page); /** ion_page_pool_shrink - shrinks the size of the memory cached in the pool diff --git a/drivers/staging/android/ion/ion_cma_heap.c b/drivers/staging/android/ion/ion_cma_heap.c index 49718c96bf9e..82e80621d114 100644 --- a/drivers/staging/android/ion/ion_cma_heap.c +++ b/drivers/staging/android/ion/ion_cma_heap.c @@ -59,6 +59,9 @@ static int ion_cma_allocate(struct ion_heap *heap, struct ion_buffer *buffer, memset(page_address(pages), 0, size); } + if (!ion_buffer_cached(buffer)) + ion_pages_sync_for_device(pages, size, DMA_BIDIRECTIONAL); + table = kmalloc(sizeof(*table), GFP_KERNEL); if (!table) goto err; diff --git a/drivers/staging/android/ion/ion_page_pool.c b/drivers/staging/android/ion/ion_page_pool.c index b3017f12835f..169a321778ed 100644 --- a/drivers/staging/android/ion/ion_page_pool.c +++ b/drivers/staging/android/ion/ion_page_pool.c @@ -63,7 +63,7 @@ static struct page *ion_page_pool_remove(struct ion_page_pool *pool, bool high) return page; } -struct page *ion_page_pool_alloc(struct ion_page_pool *pool) +struct page *ion_page_pool_alloc(struct ion_page_pool *pool, bool *from_pool) { struct page *page = NULL; @@ -76,8 +76,12 @@ struct page *ion_page_pool_alloc(struct ion_page_pool *pool) page = ion_page_pool_remove(pool, false); mutex_unlock(&pool->mutex); - if (!page) + if (!page) { page = ion_page_pool_alloc_pages(pool); + *from_pool = false; + } else { + *from_pool = true; + } return page; } diff --git a/drivers/staging/android/ion/ion_system_heap.c b/drivers/staging/android/ion/ion_system_heap.c index bc19cdd30637..3bb4604e032b 100644 --- a/drivers/staging/android/ion/ion_system_heap.c +++ b/drivers/staging/android/ion/ion_system_heap.c @@ -57,13 +57,18 @@ static struct page *alloc_buffer_page(struct ion_system_heap *heap, bool cached = ion_buffer_cached(buffer); struct ion_page_pool *pool; struct page *page; + bool from_pool; if (!cached) pool = heap->uncached_pools[order_to_index(order)]; else pool = heap->cached_pools[order_to_index(order)]; - page = ion_page_pool_alloc(pool); + page = ion_page_pool_alloc(pool, &from_pool); + + if (!from_pool && !ion_buffer_cached(buffer)) + ion_pages_sync_for_device(page, PAGE_SIZE << order, + DMA_BIDIRECTIONAL); return page; } -- 1.8.5.2 Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project

6 years

Re: [Linaro-mm-sig] [PATCH 1/8] dma-buf: remove shared fence staging in reservation object

by Christian König

Ping! Adding a few people directly and more mailing lists. Can I get an acked-by/rb for this? It's only a cleanup and not much functional change. Regards, Christian. Am 04.10.2018 um 15:12 schrieb Christian König: > No need for that any more. Just replace the list when there isn't enough > room any more for the additional fence. > > Signed-off-by: Christian König <christian.koenig(a)amd.com> > --- > drivers/dma-buf/reservation.c | 178 ++++++++++++++---------------------------- > include/linux/reservation.h | 4 - > 2 files changed, 58 insertions(+), 124 deletions(-) > > diff --git a/drivers/dma-buf/reservation.c b/drivers/dma-buf/reservation.c > index 6c95f61a32e7..5825fc336a13 100644 > --- a/drivers/dma-buf/reservation.c > +++ b/drivers/dma-buf/reservation.c > @@ -68,105 +68,23 @@ EXPORT_SYMBOL(reservation_seqcount_string); > */ > int reservation_object_reserve_shared(struct reservation_object *obj) > { > - struct reservation_object_list *fobj, *old; > - u32 max; > + struct reservation_object_list *old, *new; > + unsigned int i, j, k, max; > > old = reservation_object_get_list(obj); > > if (old && old->shared_max) { > - if (old->shared_count < old->shared_max) { > - /* perform an in-place update */ > - kfree(obj->staged); > - obj->staged = NULL; > + if (old->shared_count < old->shared_max) > return 0; > - } else > + else > max = old->shared_max * 2; > - } else > - max = 4; > - > - /* > - * resize obj->staged or allocate if it doesn't exist, > - * noop if already correct size > - */ > - fobj = krealloc(obj->staged, offsetof(typeof(*fobj), shared[max]), > - GFP_KERNEL); > - if (!fobj) > - return -ENOMEM; > - > - obj->staged = fobj; > - fobj->shared_max = max; > - return 0; > -} > -EXPORT_SYMBOL(reservation_object_reserve_shared); > - > -static void > -reservation_object_add_shared_inplace(struct reservation_object *obj, > - struct reservation_object_list *fobj, > - struct dma_fence *fence) > -{ > - struct dma_fence *signaled = NULL; > - u32 i, signaled_idx; > - > - dma_fence_get(fence); > - > - preempt_disable(); > - write_seqcount_begin(&obj->seq); > - > - for (i = 0; i < fobj->shared_count; ++i) { > - struct dma_fence *old_fence; > - > - old_fence = rcu_dereference_protected(fobj->shared[i], > - reservation_object_held(obj)); > - > - if (old_fence->context == fence->context) { > - /* memory barrier is added by write_seqcount_begin */ > - RCU_INIT_POINTER(fobj->shared[i], fence); > - write_seqcount_end(&obj->seq); > - preempt_enable(); > - > - dma_fence_put(old_fence); > - return; > - } > - > - if (!signaled && dma_fence_is_signaled(old_fence)) { > - signaled = old_fence; > - signaled_idx = i; > - } > - } > - > - /* > - * memory barrier is added by write_seqcount_begin, > - * fobj->shared_count is protected by this lock too > - */ > - if (signaled) { > - RCU_INIT_POINTER(fobj->shared[signaled_idx], fence); > } else { > - BUG_ON(fobj->shared_count >= fobj->shared_max); > - RCU_INIT_POINTER(fobj->shared[fobj->shared_count], fence); > - fobj->shared_count++; > + max = 4; > } > > - write_seqcount_end(&obj->seq); > - preempt_enable(); > - > - dma_fence_put(signaled); > -} > - > -static void > -reservation_object_add_shared_replace(struct reservation_object *obj, > - struct reservation_object_list *old, > - struct reservation_object_list *fobj, > - struct dma_fence *fence) > -{ > - unsigned i, j, k; > - > - dma_fence_get(fence); > - > - if (!old) { > - RCU_INIT_POINTER(fobj->shared[0], fence); > - fobj->shared_count = 1; > - goto done; > - } > + new = kmalloc(offsetof(typeof(*new), shared[max]), GFP_KERNEL); > + if (!new) > + return -ENOMEM; > > /* > * no need to bump fence refcounts, rcu_read access > @@ -174,46 +92,45 @@ reservation_object_add_shared_replace(struct reservation_object *obj, > * references from the old struct are carried over to > * the new. > */ > - for (i = 0, j = 0, k = fobj->shared_max; i < old->shared_count; ++i) { > - struct dma_fence *check; > + for (i = 0, j = 0, k = max; i < (old ? old->shared_count : 0); ++i) { > + struct dma_fence *fence; > > - check = rcu_dereference_protected(old->shared[i], > - reservation_object_held(obj)); > - > - if (check->context == fence->context || > - dma_fence_is_signaled(check)) > - RCU_INIT_POINTER(fobj->shared[--k], check); > + fence = rcu_dereference_protected(old->shared[i], > + reservation_object_held(obj)); > + if (dma_fence_is_signaled(fence)) > + RCU_INIT_POINTER(new->shared[--k], fence); > else > - RCU_INIT_POINTER(fobj->shared[j++], check); > + RCU_INIT_POINTER(new->shared[j++], fence); > } > - fobj->shared_count = j; > - RCU_INIT_POINTER(fobj->shared[fobj->shared_count], fence); > - fobj->shared_count++; > + new->shared_count = j; > + new->shared_max = max; > > -done: > preempt_disable(); > write_seqcount_begin(&obj->seq); > /* > * RCU_INIT_POINTER can be used here, > * seqcount provides the necessary barriers > */ > - RCU_INIT_POINTER(obj->fence, fobj); > + RCU_INIT_POINTER(obj->fence, new); > write_seqcount_end(&obj->seq); > preempt_enable(); > > if (!old) > - return; > + return 0; > > /* Drop the references to the signaled fences */ > - for (i = k; i < fobj->shared_max; ++i) { > - struct dma_fence *f; > + for (i = k; i < new->shared_max; ++i) { > + struct dma_fence *fence; > > - f = rcu_dereference_protected(fobj->shared[i], > - reservation_object_held(obj)); > - dma_fence_put(f); > + fence = rcu_dereference_protected(new->shared[i], > + reservation_object_held(obj)); > + dma_fence_put(fence); > } > kfree_rcu(old, rcu); > + > + return 0; > } > +EXPORT_SYMBOL(reservation_object_reserve_shared); > > /** > * reservation_object_add_shared_fence - Add a fence to a shared slot > @@ -226,15 +143,39 @@ reservation_object_add_shared_replace(struct reservation_object *obj, > void reservation_object_add_shared_fence(struct reservation_object *obj, > struct dma_fence *fence) > { > - struct reservation_object_list *old, *fobj = obj->staged; > + struct reservation_object_list *fobj; > + unsigned int i; > > - old = reservation_object_get_list(obj); > - obj->staged = NULL; > + dma_fence_get(fence); > + > + fobj = reservation_object_get_list(obj); > > - if (!fobj) > - reservation_object_add_shared_inplace(obj, old, fence); > - else > - reservation_object_add_shared_replace(obj, old, fobj, fence); > + preempt_disable(); > + write_seqcount_begin(&obj->seq); > + > + for (i = 0; i < fobj->shared_count; ++i) { > + struct dma_fence *old_fence; > + > + old_fence = rcu_dereference_protected(fobj->shared[i], > + reservation_object_held(obj)); > + if (old_fence->context == fence->context || > + dma_fence_is_signaled(old_fence)) { > + dma_fence_put(old_fence); > + goto replace; > + } > + } > + > + BUG_ON(fobj->shared_count >= fobj->shared_max); > + fobj->shared_count++; > + > +replace: > + /* > + * memory barrier is added by write_seqcount_begin, > + * fobj->shared_count is protected by this lock too > + */ > + RCU_INIT_POINTER(fobj->shared[i], fence); > + write_seqcount_end(&obj->seq); > + preempt_enable(); > } > EXPORT_SYMBOL(reservation_object_add_shared_fence); > > @@ -343,9 +284,6 @@ int reservation_object_copy_fences(struct reservation_object *dst, > new = dma_fence_get_rcu_safe(&src->fence_excl); > rcu_read_unlock(); > > - kfree(dst->staged); > - dst->staged = NULL; > - > src_list = reservation_object_get_list(dst); > old = reservation_object_get_excl(dst); > > diff --git a/include/linux/reservation.h b/include/linux/reservation.h > index 02166e815afb..54cf6773a14c 100644 > --- a/include/linux/reservation.h > +++ b/include/linux/reservation.h > @@ -68,7 +68,6 @@ struct reservation_object_list { > * @seq: sequence count for managing RCU read-side synchronization > * @fence_excl: the exclusive fence, if there is one currently > * @fence: list of current shared fences > - * @staged: staged copy of shared fences for RCU updates > */ > struct reservation_object { > struct ww_mutex lock; > @@ -76,7 +75,6 @@ struct reservation_object { > > struct dma_fence __rcu *fence_excl; > struct reservation_object_list __rcu *fence; > - struct reservation_object_list *staged; > }; > > #define reservation_object_held(obj) lockdep_is_held(&(obj)->lock.base) > @@ -95,7 +93,6 @@ reservation_object_init(struct reservation_object *obj) > __seqcount_init(&obj->seq, reservation_seqcount_string, &reservation_seqcount_class); > RCU_INIT_POINTER(obj->fence, NULL); > RCU_INIT_POINTER(obj->fence_excl, NULL); > - obj->staged = NULL; > } > > /** > @@ -124,7 +121,6 @@ reservation_object_fini(struct reservation_object *obj) > > kfree(fobj); > } > - kfree(obj->staged); > > ww_mutex_destroy(&obj->lock); > }

6 years, 2 months

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Linaro-mm-sig October 2018