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/* SPDX-License-Identifier: MIT */
/*
* Copyright © 2022 Intel Corporation
*/
#ifndef _XE_MIGRATE_DOC_H_
#define _XE_MIGRATE_DOC_H_
/**
* DOC: Migrate Layer
*
* The XE migrate layer is used generate jobs which can copy memory (eviction),
* clear memory, or program tables (binds). This layer exists in every GT, has
* a migrate engine, and uses a special VM for all generated jobs.
*
* Special VM details
* ==================
*
* The special VM is configured with a page structure where we can dynamically
* map BOs which need to be copied and cleared, dynamically map other VM's page
* table BOs for updates, and identity map the entire device's VRAM with 1 GB
* pages.
*
* Currently the page structure consists of 32 physical pages with 16 being
* reserved for BO mapping during copies and clear, 1 reserved for kernel binds,
* several pages are needed to setup the identity mappings (exact number based
* on how many bits of address space the device has), and the rest are reserved
* user bind operations.
*
* TODO: Diagram of layout
*
* Bind jobs
* =========
*
* A bind job consist of two batches and runs either on the migrate engine
* (kernel binds) or the bind engine passed in (user binds). In both cases the
* VM of the engine is the migrate VM.
*
* The first batch is used to update the migration VM page structure to point to
* the bind VM page table BOs which need to be updated. A physical page is
* required for this. If it is a user bind, the page is allocated from pool of
* pages reserved user bind operations with drm_suballoc managing this pool. If
* it is a kernel bind, the page reserved for kernel binds is used.
*
* The first batch is only required for devices without VRAM as when the device
* has VRAM the bind VM page table BOs are in VRAM and the identity mapping can
* be used.
*
* The second batch is used to program page table updated in the bind VM. Why
* not just one batch? Well the TLBs need to be invalidated between these two
* batches and that only can be done from the ring.
*
* When the bind job complete, the page allocated is returned the pool of pages
* reserved for user bind operations if a user bind. No need do this for kernel
* binds as the reserved kernel page is serially used by each job.
*
* Copy / clear jobs
* =================
*
* A copy or clear job consist of two batches and runs on the migrate engine.
*
* Like binds, the first batch is used update the migration VM page structure.
* In copy jobs, we need to map the source and destination of the BO into page
* the structure. In clear jobs, we just need to add 1 mapping of BO into the
* page structure. We use the 16 reserved pages in migration VM for mappings,
* this gives us a maximum copy size of 16 MB and maximum clear size of 32 MB.
*
* The second batch is used do either do the copy or clear. Again similar to
* binds, two batches are required as the TLBs need to be invalidated from the
* ring between the batches.
*
* More than one job will be generated if the BO is larger than maximum copy /
* clear size.
*
* Future work
* ===========
*
* Update copy and clear code to use identity mapped VRAM.
*
* Can we rework the use of the pages async binds to use all the entries in each
* page?
*
* Using large pages for sysmem mappings.
*
* Is it possible to identity map the sysmem? We should explore this.
*/
#endif
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