Re: [PATCH v4 24/33] drm/xe: Add GPUSVM device memory copy vfunc functions

["Thomas Hellström" <thomas.hellstrom@linux.intel.com>]

On Wed, 2025-01-29 at 11:52 -0800, Matthew Brost wrote:
> Add GPUSVM device memory copy vfunc functions and connect to
> migration
> layer. Used for device memory migration.
> 
> v2:
>  - Allow NULL device pages in xe_svm_copy
>  - Use new drm_gpusvm_devmem_ops
> v3:
>  - Prefix defines with XE_ (Thomas)
>  - Change copy chunk size to 8M
>  - Add a bunch of comments to xe_svm_copy to clarify behavior
> (Thomas)
>  - Better commit message (Thomas)
> 
> Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>

> ---
>  drivers/gpu/drm/xe/xe_svm.c | 179
> ++++++++++++++++++++++++++++++++++++
>  1 file changed, 179 insertions(+)
> 
> diff --git a/drivers/gpu/drm/xe/xe_svm.c
> b/drivers/gpu/drm/xe/xe_svm.c
> index 869a155fc9f7..222d252521f8 100644
> --- a/drivers/gpu/drm/xe/xe_svm.c
> +++ b/drivers/gpu/drm/xe/xe_svm.c
> @@ -4,6 +4,7 @@
>   */
>  
>  #include "xe_gt_tlb_invalidation.h"
> +#include "xe_migrate.h"
>  #include "xe_pt.h"
>  #include "xe_svm.h"
>  #include "xe_vm.h"
> @@ -282,6 +283,184 @@ static void
> xe_svm_garbage_collector_work_func(struct work_struct *w)
>  	up_write(&vm->lock);
>  }
>  
> +static struct xe_mem_region *page_to_mr(struct page *page)
> +{
> +	return container_of(page->pgmap, struct xe_mem_region,
> pagemap);
> +}
> +
> +static struct xe_tile *mr_to_tile(struct xe_mem_region *mr)
> +{
> +	return container_of(mr, struct xe_tile, mem.vram);
> +}
> +
> +static u64 xe_mem_region_page_to_dpa(struct xe_mem_region *mr,
> +				     struct page *page)
> +{
> +	u64 dpa;
> +	struct xe_tile *tile = mr_to_tile(mr);
> +	u64 pfn = page_to_pfn(page);
> +	u64 offset;
> +
> +	xe_tile_assert(tile, is_device_private_page(page));
> +	xe_tile_assert(tile, (pfn << PAGE_SHIFT) >= mr->hpa_base);
> +
> +	offset = (pfn << PAGE_SHIFT) - mr->hpa_base;
> +	dpa = mr->dpa_base + offset;
> +
> +	return dpa;
> +}
> +
> +enum xe_svm_copy_dir {
> +	XE_SVM_COPY_TO_VRAM,
> +	XE_SVM_COPY_TO_SRAM,
> +};
> +
> +static int xe_svm_copy(struct page **pages, dma_addr_t *dma_addr,
> +		       unsigned long npages, const enum
> xe_svm_copy_dir dir)
> +{
> +	struct xe_mem_region *mr = NULL;
> +	struct xe_tile *tile;
> +	struct dma_fence *fence = NULL;
> +	unsigned long i;
> +#define XE_VRAM_ADDR_INVALID	~0x0ull
> +	u64 vram_addr = XE_VRAM_ADDR_INVALID;
> +	int err = 0, pos = 0;
> +	bool sram = dir == XE_SVM_COPY_TO_SRAM;
> +
> +	/*
> +	 * This flow is complex: it locates physically contiguous
> device pages,
> +	 * derives the starting physical address, and performs a
> single GPU copy
> +	 * to for every 8M chunk in a DMA address array. Both device
> pages and
> +	 * DMA addresses may be sparsely populated. If either is
> NULL, a copy is
> +	 * triggered based on the current search state. The last GPU
> copy is
> +	 * waited on to ensure all copies are complete.
> +	 */
> +
> +	for (i = 0; i < npages; ++i) {
> +		struct page *spage = pages[i];
> +		struct dma_fence *__fence;
> +		u64 __vram_addr;
> +		bool match = false, chunk, last;
> +
> +#define XE_MIGRATE_CHUNK_SIZE	SZ_8M
> +		chunk = (i - pos) == (XE_MIGRATE_CHUNK_SIZE /
> PAGE_SIZE);
> +		last = (i + 1) == npages;
> +
> +		/* No CPU page and no device pages queue'd to copy
> */
> +		if (!dma_addr[i] && vram_addr ==
> XE_VRAM_ADDR_INVALID)
> +			continue;
> +
> +		if (!mr && spage) {
> +			mr = page_to_mr(spage);
> +			tile = mr_to_tile(mr);
> +		}
> +		XE_WARN_ON(spage && page_to_mr(spage) != mr);
> +
> +		/*
> +		 * CPU page and device page valid, capture physical
> address on
> +		 * first device page, check if physical contiguous
> on subsequent
> +		 * device pages.
> +		 */
> +		if (dma_addr[i] && spage) {
> +			__vram_addr = xe_mem_region_page_to_dpa(mr,
> spage);
> +			if (vram_addr == XE_VRAM_ADDR_INVALID) {
> +				vram_addr = __vram_addr;
> +				pos = i;
> +			}
> +
> +			match = vram_addr + PAGE_SIZE * (i - pos) ==
> __vram_addr;
> +		}
> +
> +		/*
> +		 * Mismatched physical address, 8M copy chunk, or
> last page -
> +		 * trigger a copy.
> +		 */
> +		if (!match || chunk || last) {
> +			/*
> +			 * Extra page for first copy if last page
> and matching
> +			 * physical address.
> +			 */
> +			int incr = (match && last) ? 1 : 0;
> +
> +			if (vram_addr != XE_VRAM_ADDR_INVALID) {
> +				if (sram)
> +					__fence =
> xe_migrate_from_vram(tile->migrate,
> +								    
>    i - pos + incr,
> +								    
>    vram_addr,
> +								    
>    dma_addr + pos);
> +				else
> +					__fence =
> xe_migrate_to_vram(tile->migrate,
> +								    
> i - pos + incr,
> +								    
> dma_addr + pos,
> +								    
> vram_addr);
> +				if (IS_ERR(__fence)) {
> +					err = PTR_ERR(__fence);
> +					goto err_out;
> +				}
> +
> +				dma_fence_put(fence);
> +				fence = __fence;
> +			}
> +
> +			/* Setup physical address of next device
> page */
> +			if (dma_addr[i] && spage) {
> +				vram_addr = __vram_addr;
> +				pos = i;
> +			} else {
> +				vram_addr = XE_VRAM_ADDR_INVALID;
> +			}
> +
> +			/* Extra mismatched device page, copy it */
> +			if (!match && last && vram_addr !=
> XE_VRAM_ADDR_INVALID) {
> +				if (sram)
> +					__fence =
> xe_migrate_from_vram(tile->migrate, 1,
> +								    
>    vram_addr,
> +								    
>    dma_addr + pos);
> +				else
> +					__fence =
> xe_migrate_to_vram(tile->migrate, 1,
> +								    
> dma_addr + pos,
> +								    
> vram_addr);
> +				if (IS_ERR(__fence)) {
> +					err = PTR_ERR(__fence);
> +					goto err_out;
> +				}
> +
> +				dma_fence_put(fence);
> +				fence = __fence;
> +			}
> +		}
> +	}
> +
> +err_out:
> +	/* Wait for all copies to complete */
> +	if (fence) {
> +		dma_fence_wait(fence, false);
> +		dma_fence_put(fence);
> +	}
> +
> +	return err;
> +#undef XE_MIGRATE_CHUNK_SIZE
> +#undef XE_VRAM_ADDR_INVALID
> +}
> +
> +static int xe_svm_copy_to_devmem(struct page **pages, dma_addr_t
> *dma_addr,
> +				 unsigned long npages)
> +{
> +	return xe_svm_copy(pages, dma_addr, npages,
> XE_SVM_COPY_TO_VRAM);
> +}
> +
> +static int xe_svm_copy_to_ram(struct page **pages, dma_addr_t
> *dma_addr,
> +			      unsigned long npages)
> +{
> +	return xe_svm_copy(pages, dma_addr, npages,
> XE_SVM_COPY_TO_SRAM);
> +}
> +
> +__maybe_unused
> +static const struct drm_gpusvm_devmem_ops gpusvm_devmem_ops = {
> +	.copy_to_devmem = xe_svm_copy_to_devmem,
> +	.copy_to_ram = xe_svm_copy_to_ram,
> +};
> +
>  static const struct drm_gpusvm_ops gpusvm_ops = {
>  	.range_alloc = xe_svm_range_alloc,
>  	.range_free = xe_svm_range_free,