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The VMA offset manager uses a device-global address-space. Hence, any
user can currently map any offset-node they want. They only need to guess
the right offset. If we wanted per open-file offset spaces, we'd either
need VM_NONLINEAR mappings or multiple "struct address_space" trees. As
both doesn't really scale, we implement access management in the VMA
manager itself.
We use an rb-tree to store open-files for each VMA node. On each mmap
call, GEM, TTM or the drivers must check whether the current user is
allowed to map this file.
We add a separate lock for each node as there is no generic lock available
for the caller to protect the node easily.
As we currently don't know whether an object may be used for mmap(), we
have to do access management for all objects. If it turns out to slow down
handle creation/deletion significantly, we can optimize it in several
ways:
- Most times only a single filp is added per bo so we could use a static
"struct file *main_filp" which is checked/added/removed first before we
fall back to the rbtree+drm_vma_offset_file.
This could be even done lockless with rcu.
- Let user-space pass a hint whether mmap() should be supported on the
bo and avoid access-management if not.
- .. there are probably more ideas once we have benchmarks ..
v2: add drm_vma_node_verify_access() helper
Signed-off-by: David Herrmann <dh.herrmann@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
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Add a "best_match" flag similar to the drm_mm_search_*() helpers so we
can convert TTM to use them in follow up patches. We can also inline the
non-generic helpers and move them into the header to allow compile-time
optimizations.
To make calls to drm_mm_{search,insert}_node() more readable, this
converts the boolean argument to a flagset. There are pending patches that
add additional flags for top-down allocators and more.
v2:
- use flag parameter instead of boolean "best_match"
- convert *_search_free() helpers to also use flags argument
Signed-off-by: David Herrmann <dh.herrmann@gmail.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Dave Airlie <airlied@redhat.com>
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If we want to map GPU memory into user-space, we need to linearize the
addresses to not confuse mm-core. Currently, GEM and TTM both implement
their own offset-managers to assign a pgoff to each object for user-space
CPU access. GEM uses a hash-table, TTM uses an rbtree.
This patch provides a unified implementation that can be used to replace
both. TTM allows partial mmaps with a given offset, so we cannot use
hashtables as the start address may not be known at mmap time. Hence, we
use the rbtree-implementation of TTM.
We could easily update drm_mm to use an rbtree instead of a linked list
for it's object list and thus drop the rbtree from the vma-manager.
However, this would slow down drm_mm object allocation for all other
use-cases (rbtree insertion) and add another 4-8 bytes to each mm node.
Hence, use the separate tree but allow for later migration.
This is a rewrite of the 2012-proposal by David Airlie <airlied@linux.ie>
v2:
- fix Docbook integration
- drop drm_mm_node_linked() and use drm_mm_node_allocated()
- remove unjustified likely/unlikely usage (but keep for rbtree paths)
- remove BUG_ON() as drm_mm already does that
- clarify page-based vs. byte-based addresses
- use drm_vma_node_reset() for initialization, too
v4:
- allow external locking via drm_vma_offset_un/lock_lookup()
- add locked lookup helper drm_vma_offset_lookup_locked()
v5:
- fix drm_vma_offset_lookup() to correctly validate range-mismatches
(fix (offset > start + pages))
- fix drm_vma_offset_exact_lookup() to actually do what it says
- remove redundant vm_pages member (add drm_vma_node_size() helper)
- remove unneeded goto
- fix documentation
Signed-off-by: David Herrmann <dh.herrmann@gmail.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Dave Airlie <airlied@gmail.com>
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