[RFC PATCH 15/15] nvme-pci: Allow mmaping the CMB in userspace

[Logan Gunthorpe <logang@deltatee.com>]

Allow userspace to obtain CMB memory by mmaping the controller's
char device. The mmap call allocates and returns a hunk of CMB memory,
(the offset is ignored) so userspace does not have control over the
address within the CMB.

A VMA allocated in this way will only be usable by drivers that set
FOLL_PCI_P2PDMA when calling GUP. And inter-device support will be
checked the first time the pages are mapped for DMA.

Currently this is only supported by O_DIRECT to an PCI NVMe device
or through the NVMe passthrough IOCTL.

Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
---
 drivers/nvme/host/core.c | 11 +++++++++++
 drivers/nvme/host/nvme.h |  1 +
 drivers/nvme/host/pci.c  |  9 +++++++++
 3 files changed, 21 insertions(+)

diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index f14316c9b34a..fc642aba671d 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -3240,12 +3240,23 @@ static long nvme_dev_ioctl(struct file *file, unsigned int cmd,
 	}
 }
 
+static int nvme_dev_mmap(struct file *file, struct vm_area_struct *vma)
+{
+	struct nvme_ctrl *ctrl = file->private_data;
+
+	if (!ctrl->ops->mmap_cmb)
+		return -ENODEV;
+
+	return ctrl->ops->mmap_cmb(ctrl, vma);
+}
+
 static const struct file_operations nvme_dev_fops = {
 	.owner		= THIS_MODULE,
 	.open		= nvme_dev_open,
 	.release	= nvme_dev_release,
 	.unlocked_ioctl	= nvme_dev_ioctl,
 	.compat_ioctl	= compat_ptr_ioctl,
+	.mmap		= nvme_dev_mmap,
 };
 
 static ssize_t nvme_sysfs_reset(struct device *dev,
diff --git a/drivers/nvme/host/nvme.h b/drivers/nvme/host/nvme.h
index a0bfe8709cfc..3d790d849701 100644
--- a/drivers/nvme/host/nvme.h
+++ b/drivers/nvme/host/nvme.h
@@ -473,6 +473,7 @@ struct nvme_ctrl_ops {
 	void (*delete_ctrl)(struct nvme_ctrl *ctrl);
 	int (*get_address)(struct nvme_ctrl *ctrl, char *buf, int size);
 	bool (*supports_pci_p2pdma)(struct nvme_ctrl *ctrl);
+	int (*mmap_cmb)(struct nvme_ctrl *ctrl, struct vm_area_struct *vma);
 };
 
 #ifdef CONFIG_FAULT_INJECTION_DEBUG_FS
diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
index 26976bdf4af0..9c61573111ea 100644
--- a/drivers/nvme/host/pci.c
+++ b/drivers/nvme/host/pci.c
@@ -2687,6 +2687,14 @@ static bool nvme_pci_supports_pci_p2pdma(struct nvme_ctrl *ctrl)
 	return dma_pci_p2pdma_supported(dev->dev);
 }
 
+static int nvme_pci_mmap_cmb(struct nvme_ctrl *ctrl,
+			     struct vm_area_struct *vma)
+{
+	struct pci_dev *pdev = to_pci_dev(to_nvme_dev(ctrl)->dev);
+
+	return pci_mmap_p2pmem(pdev, vma);
+}
+
 static const struct nvme_ctrl_ops nvme_pci_ctrl_ops = {
 	.name			= "pcie",
 	.module			= THIS_MODULE,
@@ -2698,6 +2706,7 @@ static const struct nvme_ctrl_ops nvme_pci_ctrl_ops = {
 	.submit_async_event	= nvme_pci_submit_async_event,
 	.get_address		= nvme_pci_get_address,
 	.supports_pci_p2pdma	= nvme_pci_supports_pci_p2pdma,
+	.mmap_cmb		= nvme_pci_mmap_cmb,
 };
 
 static int nvme_dev_map(struct nvme_dev *dev)
-- 
2.20.1