[PATCH v2 11/11] mm/hmm: add an helper function that fault pages and map them to a device v2

[jglisse]

From: JÃrÃme Glisse <jglisse@xxxxxxxxxx>

This is a all in one helper that fault pages in a range and map them to
a device so that every single device driver do not have to re-implement
this common pattern.

This is taken from ODP RDMA in preparation of ODP RDMA convertion. It
will be use by nouveau and other drivers.

Changes since v1:
    - improved commit message

Signed-off-by: JÃrÃme Glisse <jglisse@xxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Ralph Campbell <rcampbell@xxxxxxxxxx>
Cc: John Hubbard <jhubbard@xxxxxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
---
 include/linux/hmm.h |   9 +++
 mm/hmm.c            | 152 ++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 161 insertions(+)

diff --git a/include/linux/hmm.h b/include/linux/hmm.h
index 5f9deaeb9d77..7aadf18b29cb 100644
--- a/include/linux/hmm.h
+++ b/include/linux/hmm.h
@@ -568,6 +568,15 @@ int hmm_range_register(struct hmm_range *range,
 void hmm_range_unregister(struct hmm_range *range);
 long hmm_range_snapshot(struct hmm_range *range);
 long hmm_range_fault(struct hmm_range *range, bool block);
+long hmm_range_dma_map(struct hmm_range *range,
+		       struct device *device,
+		       dma_addr_t *daddrs,
+		       bool block);
+long hmm_range_dma_unmap(struct hmm_range *range,
+			 struct vm_area_struct *vma,
+			 struct device *device,
+			 dma_addr_t *daddrs,
+			 bool dirty);
 
 /*
  * HMM_RANGE_DEFAULT_TIMEOUT - default timeout (ms) when waiting for a range
diff --git a/mm/hmm.c b/mm/hmm.c
index ce33151c6832..fd143251b157 100644
--- a/mm/hmm.c
+++ b/mm/hmm.c
@@ -30,6 +30,7 @@
 #include <linux/hugetlb.h>
 #include <linux/memremap.h>
 #include <linux/jump_label.h>
+#include <linux/dma-mapping.h>
 #include <linux/mmu_notifier.h>
 #include <linux/memory_hotplug.h>
 
@@ -1163,6 +1164,157 @@ long hmm_range_fault(struct hmm_range *range, bool block)
 	return (hmm_vma_walk.last - range->start) >> PAGE_SHIFT;
 }
 EXPORT_SYMBOL(hmm_range_fault);
+
+/*
+ * hmm_range_dma_map() - hmm_range_fault() and dma map page all in one.
+ * @range: range being faulted
+ * @device: device against to dma map page to
+ * @daddrs: dma address of mapped pages
+ * @block: allow blocking on fault (if true it sleeps and do not drop mmap_sem)
+ * Returns: number of pages mapped on success, -EAGAIN if mmap_sem have been
+ *          drop and you need to try again, some other error value otherwise
+ *
+ * Note same usage pattern as hmm_range_fault().
+ */
+long hmm_range_dma_map(struct hmm_range *range,
+		       struct device *device,
+		       dma_addr_t *daddrs,
+		       bool block)
+{
+	unsigned long i, npages, mapped;
+	long ret;
+
+	ret = hmm_range_fault(range, block);
+	if (ret <= 0)
+		return ret ? ret : -EBUSY;
+
+	npages = (range->end - range->start) >> PAGE_SHIFT;
+	for (i = 0, mapped = 0; i < npages; ++i) {
+		enum dma_data_direction dir = DMA_FROM_DEVICE;
+		struct page *page;
+
+		/*
+		 * FIXME need to update DMA API to provide invalid DMA address
+		 * value instead of a function to test dma address value. This
+		 * would remove lot of dumb code duplicated accross many arch.
+		 *
+		 * For now setting it to 0 here is good enough as the pfns[]
+		 * value is what is use to check what is valid and what isn't.
+		 */
+		daddrs[i] = 0;
+
+		page = hmm_pfn_to_page(range, range->pfns[i]);
+		if (page == NULL)
+			continue;
+
+		/* Check if range is being invalidated */
+		if (!range->valid) {
+			ret = -EBUSY;
+			goto unmap;
+		}
+
+		/* If it is read and write than map bi-directional. */
+		if (range->pfns[i] & range->values[HMM_PFN_WRITE])
+			dir = DMA_BIDIRECTIONAL;
+
+		daddrs[i] = dma_map_page(device, page, 0, PAGE_SIZE, dir);
+		if (dma_mapping_error(device, daddrs[i])) {
+			ret = -EFAULT;
+			goto unmap;
+		}
+
+		mapped++;
+	}
+
+	return mapped;
+
+unmap:
+	for (npages = i, i = 0; (i < npages) && mapped; ++i) {
+		enum dma_data_direction dir = DMA_FROM_DEVICE;
+		struct page *page;
+
+		page = hmm_pfn_to_page(range, range->pfns[i]);
+		if (page == NULL)
+			continue;
+
+		if (dma_mapping_error(device, daddrs[i]))
+			continue;
+
+		/* If it is read and write than map bi-directional. */
+		if (range->pfns[i] & range->values[HMM_PFN_WRITE])
+			dir = DMA_BIDIRECTIONAL;
+
+		dma_unmap_page(device, daddrs[i], PAGE_SIZE, dir);
+		mapped--;
+	}
+
+	return ret;
+}
+EXPORT_SYMBOL(hmm_range_dma_map);
+
+/*
+ * hmm_range_dma_unmap() - unmap range of that was map with hmm_range_dma_map()
+ * @range: range being unmapped
+ * @vma: the vma against which the range (optional)
+ * @device: device against which dma map was done
+ * @daddrs: dma address of mapped pages
+ * @dirty: dirty page if it had the write flag set
+ * Returns: number of page unmapped on success, -EINVAL otherwise
+ *
+ * Note that caller MUST abide by mmu notifier or use HMM mirror and abide
+ * to the sync_cpu_device_pagetables() callback so that it is safe here to
+ * call set_page_dirty(). Caller must also take appropriate locks to avoid
+ * concurrent mmu notifier or sync_cpu_device_pagetables() to make progress.
+ */
+long hmm_range_dma_unmap(struct hmm_range *range,
+			 struct vm_area_struct *vma,
+			 struct device *device,
+			 dma_addr_t *daddrs,
+			 bool dirty)
+{
+	unsigned long i, npages;
+	long cpages = 0;
+
+	/* Sanity check. */
+	if (range->end <= range->start)
+		return -EINVAL;
+	if (!daddrs)
+		return -EINVAL;
+	if (!range->pfns)
+		return -EINVAL;
+
+	npages = (range->end - range->start) >> PAGE_SHIFT;
+	for (i = 0; i < npages; ++i) {
+		enum dma_data_direction dir = DMA_FROM_DEVICE;
+		struct page *page;
+
+		page = hmm_pfn_to_page(range, range->pfns[i]);
+		if (page == NULL)
+			continue;
+
+		/* If it is read and write than map bi-directional. */
+		if (range->pfns[i] & range->values[HMM_PFN_WRITE]) {
+			dir = DMA_BIDIRECTIONAL;
+
+			/*
+			 * See comments in function description on why it is
+			 * safe here to call set_page_dirty()
+			 */
+			if (dirty)
+				set_page_dirty(page);
+		}
+
+		/* Unmap and clear pfns/dma address */
+		dma_unmap_page(device, daddrs[i], PAGE_SIZE, dir);
+		range->pfns[i] = range->values[HMM_PFN_NONE];
+		/* FIXME see comments in hmm_vma_dma_map() */
+		daddrs[i] = 0;
+		cpages++;
+	}
+
+	return cpages;
+}
+EXPORT_SYMBOL(hmm_range_dma_unmap);
 #endif /* IS_ENABLED(CONFIG_HMM_MIRROR) */
 
 
-- 
2.17.2