NVIDIA: SAUCE: vfio/nvgrace-egm: register EGM PFNMAP range with memory_failure

EGM carveout memory is mapped directly into userspace (QEMU) and is not
added to the kernel. It is not managed by the kernel page allocator and
has no struct pages. The module can thus utilize the Linux memory manager's
memory_failure mechanism for regions with no struct pages. The Linux MM
code exposes register/unregister APIs allowing modules to register such
memory regions for memory_failure handling.

Register the EGM PFN range with the MM memory_failure infrastructure on
open, and unregister it on the last close. Provide a PFN-to-VMA offset
callback that validates the PFN is within the EGM region and the VMA,
then converts it to a file offset and records the poisoned offset in the
existing hashtable for reporting to userspace.

Signed-off-by: Ankit Agrawal <ankita@nvidia.com>

Author: ankita-nv

drivers/vfio/pci/nvgrace-gpu/egm.c

@@ -8,6 +8,7 @@
 #include <linux/egm.h>
 #include <linux/nvgrace-egm.h>
 #include <linux/vmalloc.h>
+#include <linux/memory-failure.h>
 
 #define MAX_EGM_NODES 256
 
@@ -26,6 +27,7 @@ struct egm_region {
 	struct cdev cdev;
 	struct list_head gpus;
 	DECLARE_HASHTABLE(htbl, 0x10);
+	struct pfn_address_space pfn_address_space;
 };
 
 struct h_node {
@@ -37,11 +39,97 @@ static dev_t dev;
 static struct class *class;
 static struct list_head egm_list;
 
+static int pfn_memregion_offset(struct egm_region *region,
+				unsigned long pfn,
+				pgoff_t *pfn_offset_in_region)
+{
+	unsigned long start_pfn, num_pages;
+
+	start_pfn = PHYS_PFN(region->egmphys);
+	num_pages = region->egmlength >> PAGE_SHIFT;
+
+	if (pfn < start_pfn || pfn >= start_pfn + num_pages)
+		return -EFAULT;
+
+	*pfn_offset_in_region = pfn - start_pfn;
+
+	return 0;
+}
+
+static int track_ecc_offset(struct egm_region *region,
+			    unsigned long mem_offset)
+{
+	struct h_node *cur_page, *ecc_page;
+	unsigned long bkt;
+
+	hash_for_each(region->htbl, bkt, cur_page, node) {
+		if (cur_page->mem_offset == mem_offset)
+			return 0;
+	}
+
+	ecc_page = (struct h_node *)(vzalloc(sizeof(struct h_node)));
+	if (!ecc_page)
+		return -ENOMEM;
+
+	ecc_page->mem_offset = mem_offset;
+
+	hash_add(region->htbl, &ecc_page->node, ecc_page->mem_offset);
+
+	return 0;
+}
+
+static int nvgrace_egm_pfn_to_vma_pgoff(struct vm_area_struct *vma,
+					unsigned long pfn,
+					pgoff_t *pgoff)
+{
+	struct egm_region *region = vma->vm_file->private_data;
+	pgoff_t vma_offset_in_region = vma->vm_pgoff &
+		((1U << (VFIO_PCI_OFFSET_SHIFT - PAGE_SHIFT)) - 1);
+	pgoff_t pfn_offset_in_region;
+	int ret;
+
+	ret = pfn_memregion_offset(region, pfn, &pfn_offset_in_region);
+	if (ret)
+		return ret;
+
+	/* Ensure PFN is not before VMA's start within the region */
+	if (pfn_offset_in_region < vma_offset_in_region)
+		return -EFAULT;
+
+	/* Calculate offset from VMA start */
+	*pgoff = vma->vm_pgoff +
+		 (pfn_offset_in_region - vma_offset_in_region);
+
+	/* Track and save the poisoned offset */
+	return track_ecc_offset(region, *pgoff << PAGE_SHIFT);
+}
+
+static int
+nvgrace_egm_vfio_pci_register_pfn_range(struct inode *inode,
+					struct egm_region *region)
+{
+	int ret;
+	unsigned long pfn, nr_pages;
+
+	pfn = PHYS_PFN(region->egmphys);
+	nr_pages = region->egmlength >> PAGE_SHIFT;
+
+	region->pfn_address_space.node.start = pfn;
+	region->pfn_address_space.node.last = pfn + nr_pages - 1;
+	region->pfn_address_space.mapping = inode->i_mapping;
+	region->pfn_address_space.pfn_to_vma_pgoff = nvgrace_egm_pfn_to_vma_pgoff;
+
+	ret = register_pfn_address_space(&region->pfn_address_space);
+
+	return ret;
+}
+
 static int nvgrace_egm_open(struct inode *inode, struct file *file)
 {
 	void *memaddr;
 	struct egm_region *region = container_of(inode->i_cdev,
 						 struct egm_region, cdev);
+	int ret;
 
 	if (atomic_inc_return(&region->open_count) > 1)
 		return 0;
@@ -56,6 +144,12 @@ static int nvgrace_egm_open(struct inode *inode, struct file *file)
 	memunmap(memaddr);
 	file->private_data = region;
 
+	ret = nvgrace_egm_vfio_pci_register_pfn_range(inode, region);
+	if (ret && ret != -EOPNOTSUPP) {
+		file->private_data = NULL;
+		return ret;
+	}
+
 	return 0;
 }
 
@@ -64,8 +158,11 @@ static int nvgrace_egm_release(struct inode *inode, struct file *file)
 	struct egm_region *region = container_of(inode->i_cdev,
 						 struct egm_region, cdev);
 
-	if (atomic_dec_and_test(&region->open_count))
+	if (atomic_dec_and_test(&region->open_count)) {
+		unregister_pfn_address_space(&region->pfn_address_space);
+
 		file->private_data = NULL;
+	}
 
 	return 0;
 }