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SVM allows for seamless > > > sharing of memory between the CPU and GPU, enhancing performance and > > > flexibility in GPU computing tasks. > > > > > > The patch adds the necessary infrastructure for SVM, including data > > > structures and functions for managing SVM ranges and notifiers. It also > > > provides mechanisms for allocating, deallocating, and migrating memory > > > regions between system RAM and GPU VRAM. > > > > > > This is largely inspired by GPUVM. > > > > > > v2: > > >   - Take order into account in check pages > > >   - Clear range->pages in get pages error > > >   - Drop setting dirty or accessed bit in get pages (Vetter) > > >   - Remove mmap assert for cpu faults > > >   - Drop mmap write lock abuse (Vetter, Christian) > > >   - Decouple zdd from range (Vetter, Oak) > > >   - Add drm_gpusvm_range_evict, make it work with coherent pages > > >   - Export drm_gpusvm_evict_to_sram, only use in BO evict path (Vetter) > > >   - mmget/put in drm_gpusvm_evict_to_sram > > >   - Drop range->vram_alloation variable > > >   - Don't return in drm_gpusvm_evict_to_sram until all pages detached > > >   - Don't warn on mixing sram and device pages > > >   - Update kernel doc > > >   - Add coherent page support to get pages > > >   - Use DMA_FROM_DEVICE rather than DMA_BIDIRECTIONAL > > >   - Add struct drm_gpusvm_vram and ops (Thomas) > > >   - Update the range's seqno if the range is valid (Thomas) > > >   - Remove the is_unmapped check before hmm_range_fault (Thomas) > > >   - Use drm_pagemap (Thomas) > > >   - Drop kfree_mapping (Thomas) > > >   - dma mapp pages under notifier lock (Thomas) > > >   - Remove ctx.prefault > > >   - Remove ctx.mmap_locked > > >   - Add ctx.check_pages > > >   - s/vram/devmem (Thomas) > > > v3: > > >   - Fix memory leak drm_gpusvm_range_get_pages > > >   - Only migrate pages with same zdd on CPU fault > > >   - Loop over al VMAs in drm_gpusvm_range_evict > > >   - Make GPUSVM a drm level module > > >   - GPL or MIT license > > >   - Update main kernel doc (Thomas) > > >   - Prefer foo() vs foo for functions in kernel doc (Thomas) > > >   - Prefer functions over macros (Thomas) > > >   - Use unsigned long vs u64 for addresses (Thomas) > > >   - Use standard interval_tree (Thomas) > > >   - s/drm_gpusvm_migration_put_page/ > > > drm_gpusvm_migration_unlock_put_page (Thomas) > > >   - Drop err_out label in drm_gpusvm_range_find_or_insert (Thomas) > > >   - Fix kernel doc in drm_gpusvm_range_free_pages (Thomas) > > >   - Newlines between functions defs in header file (Thomas) > > >   - Drop shall language in driver vfunc kernel doc (Thomas) > > >   - Move some static inlines from head to C file (Thomas) > > >   - Don't allocate pages under page lock in > > > drm_gpusvm_migrate_populate_ram_pfn (Thomas) > > >   - Change check_pages to a threshold > > > v4: > > >   - Fix NULL ptr deref in drm_gpusvm_migrate_populate_ram_pfn > > > (Thomas, Himal) > > >   - Fix check pages threshold > > >   - Check for range being unmapped under notifier lock in get pages > > > (Testing) > > >   - Fix characters per line > > >   - Drop WRITE_ONCE for zdd->devmem_allocation assignment (Thomas) > > >   - Use completion for devmem_allocation->detached (Thomas) > > >   - Make GPU SVM depend on ZONE_DEVICE (CI) > > >   - Use hmm_range_fault for eviction (Thomas) > > >   - Drop zdd worker (Thomas) > > > > > > Cc: Simona Vetter > > > Cc: Dave Airlie > > > Cc: Christian König > > > Cc: > > > Signed-off-by: Matthew Brost > > > Signed-off-by: Thomas Hellström > > > --- > > > > > > > > > +/** > > > + * __drm_gpusvm_migrate_to_ram() - Migrate GPU SVM range to RAM > > > (internal) > > > + * @vas: Pointer to the VM area structure > > > + * @device_private_page_owner: Device private pages owner > > > + * @page: Pointer to the page for fault handling (can be NULL) > > > + * @fault_addr: Fault address > > > + * @size: Size of migration > > > + * > > > + * This internal function performs the migration of the specified > > > GPU SVM range > > > + * to RAM. It sets up the migration, populates + dma maps RAM PFNs, and > > > + * invokes the driver-specific operations for migration to RAM. > > > + * > > > + * Returns: > > > + * 0 on success, negative error code on failure. > > > + */ > > > +static int __drm_gpusvm_migrate_to_ram(struct vm_area_struct *vas, > > > +                       void *device_private_page_owner, > > > +                       struct page *page, > > > +                       unsigned long fault_addr, > > > +                       unsigned long size) > > > +{ > > > +    struct migrate_vma migrate = { > > > +        .vma        = vas, > > > +        .pgmap_owner    = device_private_page_owner, > > > +        .flags        = MIGRATE_VMA_SELECT_DEVICE_PRIVATE | > > > +            MIGRATE_VMA_SELECT_DEVICE_COHERENT, > > > +        .fault_page    = page, > > > +    }; > > > +    struct drm_gpusvm_zdd *zdd; > > > +    const struct drm_gpusvm_devmem_ops *ops; > > > +    struct device *dev; > > > +    unsigned long npages, mpages = 0; > > > +    struct page **pages; > > > +    dma_addr_t *dma_addr; > > > +    unsigned long start, end; > > > +    void *buf; > > > +    int i, err = 0; > > > + > > > +    start = ALIGN_DOWN(fault_addr, size); > > > +    end = ALIGN(fault_addr + 1, size); > > > + > > > +    /* Corner where VMA area struct has been partially unmapped */ > > > +    if (start < vas->vm_start) > > > +        start = vas->vm_start; > > > +    if (end > vas->vm_end) > > > +        end = vas->vm_end; > > > + > > > +    migrate.start = start; > > > +    migrate.end = end; > > > +    npages = npages_in_range(start, end); > > > + > > > +    buf = kvcalloc(npages, 2 * sizeof(*migrate.src) + > > > sizeof(*dma_addr) + > > > +               sizeof(*pages), GFP_KERNEL); > > > +    if (!buf) { > > > +        err = -ENOMEM; > > > +        goto err_out; > > > +    } > > > +    dma_addr = buf + (2 * sizeof(*migrate.src) * npages); > > > +    pages = buf + (2 * sizeof(*migrate.src) + sizeof(*dma_addr)) * > > > npages; > > > + > > > +    migrate.vma = vas; > > > +    migrate.src = buf; > > > +    migrate.dst = migrate.src + npages; > > > + > > > +    err = migrate_vma_setup(&migrate); > > > +    if (err) > > > +        goto err_free; > > > + > > > +    /* Raced with another CPU fault, nothing to do */ > > > +    if (!migrate.cpages) > > > +        goto err_free; > > > + > > > +    if (!page) { > > > +        for (i = 0; i < npages; ++i) { > > > +            if (!(migrate.src[i] & MIGRATE_PFN_MIGRATE)) > > > +                continue; > > > + > > > +            page = migrate_pfn_to_page(migrate.src[i]); > > > +            break; > > > +        } > > > + > > > +        if (!page) > > > +            goto err_finalize; > > > +    } > > > +    zdd = page->zone_device_data; > > > +    ops = zdd->devmem_allocation->ops; > > > +    dev = zdd->devmem_allocation->dev; > > > + > > > +    err = drm_gpusvm_migrate_populate_ram_pfn(vas, page, npages, > > > &mpages, > > > +                          migrate.src, migrate.dst, > > > +                          start); > > > +    if (err) > > > +        goto err_finalize; > > > + > > > +    err = drm_gpusvm_migrate_map_pages(dev, dma_addr, migrate.dst, > > > npages, > > > +                       DMA_FROM_DEVICE); > > > +    if (err) > > > +        goto err_finalize; > > > + > > > +    for (i = 0; i < npages; ++i) > > > +        pages[i] = migrate_pfn_to_page(migrate.src[i]); > > > + > > > +    err = ops->copy_to_ram(pages, dma_addr, npages); > > > +    if (err) > > > +        goto err_finalize; > > > + > > > +err_finalize: > > > +    if (err) > > > +        drm_gpusvm_migration_unlock_put_pages(npages, migrate.dst); > > > +    migrate_vma_pages(&migrate); > > > +    migrate_vma_finalize(&migrate); > > > +    drm_gpusvm_migrate_unmap_pages(dev, dma_addr, npages, > > > +                       DMA_FROM_DEVICE); > > > > clang for me is throwing: > > > > drivers/gpu/drm/drm_gpusvm.c:2017:7: error: variable 'dev' is used > > uninitialized whenever 'if' condition is true [-Werror,-Wsometimes- > > uninitialized] > >  2017 |                 if (!page) > >       |                     ^~~~~ > > drivers/gpu/drm/drm_gpusvm.c:2047:33: note: uninitialized use occurs here > >  2047 |         drm_gpusvm_migrate_unmap_pages(dev, dma_addr, npages, > >       |                                        ^~~ > > drivers/gpu/drm/drm_gpusvm.c:2017:3: note: remove the 'if' if its > > condition is always false > >  2017 |                 if (!page) > >       |                 ^~~~~~~~~~ > >  2018 |                         goto err_finalize; > >       |                         ~~~~~~~~~~~~~~~~~ > > drivers/gpu/drm/drm_gpusvm.c:1966:20: note: initialize the variable > > 'dev' to silence this warning > >  1966 |         struct device *dev; > >       |                           ^ > >       |                            = NULL > > 1 error generated. > > I also reported this issue in the v3 patch, but it doesn't seem to have been > fixed in v4 yet. > > https://lore.kernel.org/dri-devel/0416fa97-1734-4565-a352-f045a6c0a15a@intel.com/ > Yea. The uninitialization is in fact harmless as drm_gpusvm_migrate_unmap_pages is a NOP in this path which I stated. I was unware a tool was complaining about this. I think get this fixed then. Thanks, Matt > Br, > > G.G. >