[PATCH v2 4/4] vfio/nvgpu: register device memory for poison handling

[ankita]

From: Ankit Agrawal <ankita@xxxxxxxxxx>

The nvgrace-gpu-vfio-pci module [1] maps the device memory to the user VA
(Qemu) using remap_pfn_range() without adding the memory to the kernel.
The device memory pages are not backed by struct page. Patches 1-3
implements the mechanism to handle ECC/poison on memory page without
struct page and expose a registration function. This new mechanism is
leveraged here.

The module registers its memory region with the kernel MM for ECC handling
using the register_pfn_address_space() registration API exposed by the
kernel. It also defines a failure callback function pfn_memory_failure()
to get the poisoned PFN from the MM.

The module track poisoned PFN using a hastable. The PFN is communicated
by the kernel MM to the module through the failure function, which push
the appropriate memory offset to the hashtable.

The module also defines a VMA fault ops for the module. It returns
VM_FAULT_HWPOISON in case the memory offset is found in the hashtable.

[1] https://lore.kernel.org/all/20231114081611.30550-1-ankita@xxxxxxxxxx/

Signed-off-by: Ankit Agrawal <ankita@xxxxxxxxxx>
---
 drivers/vfio/pci/nvgrace-gpu/main.c | 123 +++++++++++++++++++++++++++-
 drivers/vfio/vfio_main.c            |   3 +-
 2 files changed, 124 insertions(+), 2 deletions(-)

diff --git a/drivers/vfio/pci/nvgrace-gpu/main.c b/drivers/vfio/pci/nvgrace-gpu/main.c
index b8634974e5cc..5a567375bd14 100644
--- a/drivers/vfio/pci/nvgrace-gpu/main.c
+++ b/drivers/vfio/pci/nvgrace-gpu/main.c
@@ -6,6 +6,16 @@
 #include <linux/pci.h>
 #include <linux/vfio_pci_core.h>
 #include <linux/vfio.h>
+#ifdef CONFIG_MEMORY_FAILURE
+#include <linux/bitmap.h>
+#include <linux/memory-failure.h>
+#include <linux/hashtable.h>
+#endif
+
+struct h_node {
+	unsigned long mem_offset;
+	struct hlist_node node;
+};
 
 struct nvgrace_gpu_vfio_pci_core_device {
 	struct vfio_pci_core_device core_device;
@@ -13,8 +23,96 @@ struct nvgrace_gpu_vfio_pci_core_device {
 	size_t memlength;
 	void *memmap;
 	struct mutex memmap_lock;
+#ifdef CONFIG_MEMORY_FAILURE
+	struct pfn_address_space pfn_address_space;
+	DECLARE_HASHTABLE(htbl, 8);
+#endif
+};
+
+#ifdef CONFIG_MEMORY_FAILURE
+static void
+nvgrace_gpu_vfio_pci_pfn_memory_failure(struct pfn_address_space *pfn_space,
+		unsigned long pfn)
+{
+	struct nvgrace_gpu_vfio_pci_core_device *nvdev = container_of(
+		pfn_space, struct nvgrace_gpu_vfio_pci_core_device, pfn_address_space);
+	unsigned long mem_offset = pfn - pfn_space->node.start;
+	struct h_node *ecc;
+
+	if (mem_offset >= (nvdev->memlength >> PAGE_SHIFT))
+		return;
+
+	/*
+	 * MM has called to notify a poisoned page. Track that in the hastable.
+	 */
+	ecc = (struct h_node *)(vzalloc(sizeof(struct h_node)));
+	ecc->mem_offset = mem_offset;
+	hash_add(nvdev->htbl, &(ecc->node), ecc->mem_offset);
+}
+
+struct pfn_address_space_ops nvgrace_gpu_vfio_pci_pas_ops = {
+	.failure = nvgrace_gpu_vfio_pci_pfn_memory_failure,
 };
 
+static int
+nvgrace_gpu_vfio_pci_register_pfn_range(struct nvgrace_gpu_vfio_pci_core_device *nvdev,
+					struct vm_area_struct *vma)
+{
+	unsigned long nr_pages;
+	int ret = 0;
+
+	nr_pages = nvdev->memlength >> PAGE_SHIFT;
+
+	nvdev->pfn_address_space.node.start = vma->vm_pgoff;
+	nvdev->pfn_address_space.node.last = vma->vm_pgoff + nr_pages - 1;
+	nvdev->pfn_address_space.ops = &nvgrace_gpu_vfio_pci_pas_ops;
+	nvdev->pfn_address_space.mapping = vma->vm_file->f_mapping;
+
+	ret = register_pfn_address_space(&(nvdev->pfn_address_space));
+
+	return ret;
+}
+
+extern struct vfio_device *vfio_device_from_file(struct file *file);
+
+static vm_fault_t nvgrace_gpu_vfio_pci_fault(struct vm_fault *vmf)
+{
+	unsigned long mem_offset = vmf->pgoff - vmf->vma->vm_pgoff;
+	struct vfio_device *core_vdev;
+	struct nvgrace_gpu_vfio_pci_core_device *nvdev;
+	bool found = false;
+	struct h_node *cur;
+
+	if (!(vmf->vma->vm_file))
+		goto error_exit;
+
+	core_vdev = vfio_device_from_file(vmf->vma->vm_file);
+
+	if (!core_vdev)
+		goto error_exit;
+
+	nvdev = container_of(core_vdev,
+			struct nvgrace_gpu_vfio_pci_core_device, core_device.vdev);
+
+	if (mem_offset < (nvdev->memlength >> PAGE_SHIFT)) {
+		/*
+		 * Check if the page is poisoned.
+		 */
+		hash_for_each_possible(nvdev->htbl, cur, node, mem_offset) {
+			if (cur->mem_offset == mem_offset)
+				return VM_FAULT_HWPOISON;
+		}
+	}
+
+error_exit:
+	return VM_FAULT_ERROR;
+}
+
+static const struct vm_operations_struct nvgrace_gpu_vfio_pci_mmap_ops = {
+	.fault = nvgrace_gpu_vfio_pci_fault,
+};
+#endif
+
 static int nvgrace_gpu_vfio_pci_open_device(struct vfio_device *core_vdev)
 {
 	struct vfio_pci_core_device *vdev =
@@ -46,6 +144,9 @@ static void nvgrace_gpu_vfio_pci_close_device(struct vfio_device *core_vdev)
 
 	mutex_destroy(&nvdev->memmap_lock);
 
+#ifdef CONFIG_MEMORY_FAILURE
+	unregister_pfn_address_space(&(nvdev->pfn_address_space));
+#endif
 	vfio_pci_core_close_device(core_vdev);
 }
 
@@ -103,8 +204,12 @@ static int nvgrace_gpu_vfio_pci_mmap(struct vfio_device *core_vdev,
 		return ret;
 
 	vma->vm_pgoff = start_pfn;
+#ifdef CONFIG_MEMORY_FAILURE
+	vma->vm_ops = &nvgrace_gpu_vfio_pci_mmap_ops;
 
-	return 0;
+	ret = nvgrace_gpu_vfio_pci_register_pfn_range(nvdev, vma);
+#endif
+	return ret;
 }
 
 static long
@@ -413,6 +518,12 @@ nvgrace_gpu_vfio_pci_fetch_memory_property(struct pci_dev *pdev,
 
 	nvdev->memlength = memlength;
 
+#ifdef CONFIG_MEMORY_FAILURE
+	/*
+	 * Initialize the hashtable tracking the poisoned pages.
+	 */
+	hash_init(nvdev->htbl);
+#endif
 	return ret;
 }
 
@@ -448,6 +559,16 @@ static void nvgrace_gpu_vfio_pci_remove(struct pci_dev *pdev)
 {
 	struct nvgrace_gpu_vfio_pci_core_device *nvdev = nvgrace_gpu_drvdata(pdev);
 	struct vfio_pci_core_device *vdev = &nvdev->core_device;
+#ifdef CONFIG_MEMORY_FAILURE
+	struct h_node *cur;
+	unsigned long bkt;
+	struct hlist_node *tmp_node;
+
+	hash_for_each_safe(nvdev->htbl, bkt, tmp_node, cur, node) {
+		hash_del(&cur->node);
+		vfree(cur);
+	}
+#endif
 
 	vfio_pci_core_unregister_device(vdev);
 	vfio_put_device(&vdev->vdev);
diff --git a/drivers/vfio/vfio_main.c b/drivers/vfio/vfio_main.c
index 8d4995ada74a..290431ac2e00 100644
--- a/drivers/vfio/vfio_main.c
+++ b/drivers/vfio/vfio_main.c
@@ -1319,7 +1319,7 @@ const struct file_operations vfio_device_fops = {
 	.mmap		= vfio_device_fops_mmap,
 };
 
-static struct vfio_device *vfio_device_from_file(struct file *file)
+struct vfio_device *vfio_device_from_file(struct file *file)
 {
 	struct vfio_device_file *df = file->private_data;
 
@@ -1327,6 +1327,7 @@ static struct vfio_device *vfio_device_from_file(struct file *file)
 		return NULL;
 	return df->device;
 }
+EXPORT_SYMBOL_GPL(vfio_device_from_file);
 
 /**
  * vfio_file_is_valid - True if the file is valid vfio file
-- 
2.17.1