[PATCH v3 2/7] vfio: introduce vfio_dma_rw to read/write a range of IOVAs

Yan Zhao
2020-02-24T08:56:43Z

vfio_dma_rw will read/write a range of user space memory pointed to by
IOVA into/from a kernel buffer without enforcing pinning the user space
memory.

TODO: mark the IOVAs to user space memory dirty if they are written in
vfio_dma_rw().

Cc: Kevin Tian <kevin.tian@intel.com>
Signed-off-by: Yan Zhao <yan.y.zhao@intel.com>
---
drivers/vfio/vfio.c | 49 +++++++++++++++++++++
drivers/vfio/vfio_iommu_type1.c | 77 +++++++++++++++++++++++++++++++++
include/linux/vfio.h | 5 +++
3 files changed, 131 insertions(+)

diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c
index 914bdf4b9d73..902867627cbf 100644
--- a/drivers/vfio/vfio.c
+++ b/drivers/vfio/vfio.c
@@ -1998,6 +1998,55 @@ int vfio_unpin_pages(struct device *dev, unsigned long *user_pfn, int npage)
}
EXPORT_SYMBOL(vfio_unpin_pages);

+
+/*
+ * This interface allows the CPUs to perform some sort of virtual DMA on
+ * behalf of the device.
+ *
+ * CPUs read/write a range of IOVAs pointing to user space memory into/from
+ * a kernel buffer.
+ *
+ * As the read/write of user space memory is conducted via the CPUs and is
+ * not a real device DMA, it is not necessary to pin the user space memory.
+ *
+ * The caller needs to call vfio_group_get_external_user() or
+ * vfio_group_get_external_user_from_dev() prior to calling this interface,
+ * so as to prevent the VFIO group from disposal in the middle of the call.
+ * But it can keep the reference to the VFIO group for several calls into
+ * this interface.
+ * After finishing using of the VFIO group, the caller needs to release the
+ * VFIO group by calling vfio_group_put_external_user().
+ *
+ * @group [in]: vfio group of a device
+ * @iova [in] : base IOVA of a user space buffer
+ * @data [in] : pointer to kernel buffer
+ * @len [in] : kernel buffer length
+ * @write : indicate read or write
+ * Return error code on failure or 0 on success.
+ */
+int vfio_dma_rw(struct vfio_group *group, dma_addr_t iova,
+ void *data, size_t len, bool write)
+{
+ struct vfio_container *container;
+ struct vfio_iommu_driver *driver;
+ int ret = 0;
+
+ if (!group || !data || len <= 0)
+ return -EINVAL;
+
+ container = group->container;
+ driver = container->iommu_driver;
+
+ if (likely(driver && driver->ops->dma_rw))
+ ret = driver->ops->dma_rw(container->iommu_data,
+ iova, data, len, write);
+ else
+ ret = -ENOTTY;
+
+ return ret;
+}
+EXPORT_SYMBOL(vfio_dma_rw);
+
static int vfio_register_iommu_notifier(struct vfio_group *group,
unsigned long *events,
struct notifier_block *nb)
diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
index 2ada8e6cdb88..74e1c425943c 100644
--- a/drivers/vfio/vfio_iommu_type1.c
+++ b/drivers/vfio/vfio_iommu_type1.c
@@ -27,6 +27,7 @@
#include <linux/iommu.h>
#include <linux/module.h>
#include <linux/mm.h>
+#include <linux/mmu_context.h>
#include <linux/rbtree.h>
#include <linux/sched/signal.h>
#include <linux/sched/mm.h>
@@ -2326,6 +2327,81 @@ static int vfio_iommu_type1_unregister_notifier(void *iommu_data,
return blocking_notifier_chain_unregister(&iommu->notifier, nb);
}

+static size_t vfio_iommu_type1_dma_rw_chunk(struct vfio_iommu *iommu,
+ dma_addr_t iova, void *data,
+ size_t count, bool write)
+{
+ struct mm_struct *mm;
+ unsigned long vaddr;
+ struct vfio_dma *dma;
+ bool kthread = current->mm == NULL;
+ size_t done = 0;
+ size_t offset;
+
+ dma = vfio_find_dma(iommu, iova, 1);
+ if (!dma)
+ return 0;
+
+ if ((write && !(dma->prot & IOMMU_WRITE)) ||
+ !(dma->prot & IOMMU_READ))
+ return 0;
+
+ mm = get_task_mm(dma->task);
+
+ if (!mm)
+ return 0;
+
+ if (kthread)
+ use_mm(mm);
+ else if (current->mm != mm)
+ goto out;
+
+ offset = iova - dma->iova;
+
+ if (count > dma->size - offset)
+ count = dma->size - offset;
+
+ vaddr = dma->vaddr + offset;
+
+ if (write)
+ done = __copy_to_user((void __user *)vaddr,
+ data, count) ? 0 : count;
+ else
+ done = __copy_from_user(data, (void __user *)vaddr,
+ count) ? 0 : count;
+
+ if (kthread)
+ unuse_mm(mm);
+out:
+ mmput(mm);
+ return done;
+}
+
+static int vfio_iommu_type1_dma_rw(void *iommu_data, dma_addr_t iova,
+ void *data, size_t count, bool write)
+{
+ struct vfio_iommu *iommu = iommu_data;
+ int ret = 0;
+ size_t done = 0;
+
+ mutex_lock(&iommu->lock);
+ while (count > 0) {
+ done = vfio_iommu_type1_dma_rw_chunk(iommu, iova, data,
+ count, write);
+ if (!done) {
+ ret = -EFAULT;
+ break;
+ }
+
+ count -= done;
+ data += done;
+ iova += done;
+ }
+
+ mutex_unlock(&iommu->lock);
+ return ret;
+}
+
static const struct vfio_iommu_driver_ops vfio_iommu_driver_ops_type1 = {
.name = "vfio-iommu-type1",
.owner = THIS_MODULE,
@@ -2338,6 +2414,7 @@ static const struct vfio_iommu_driver_ops vfio_iommu_driver_ops_type1 = {
.unpin_pages = vfio_iommu_type1_unpin_pages,
.register_notifier = vfio_iommu_type1_register_notifier,
.unregister_notifier = vfio_iommu_type1_unregister_notifier,
+ .dma_rw = vfio_iommu_type1_dma_rw,
};

static int __init vfio_iommu_type1_init(void)
diff --git a/include/linux/vfio.h b/include/linux/vfio.h
index 2e1fa0c7396f..fea0cb1e61d2 100644
--- a/include/linux/vfio.h
+++ b/include/linux/vfio.h
@@ -82,6 +82,8 @@ struct vfio_iommu_driver_ops {
struct notifier_block *nb);
int (*unregister_notifier)(void *iommu_data,
struct notifier_block *nb);
+ int (*dma_rw)(void *iommu_data, dma_addr_t iova,
+ void *data, size_t count, bool write);
};

extern int vfio_register_iommu_driver(const struct vfio_iommu_driver_ops *ops);
@@ -109,6 +111,9 @@ extern int vfio_pin_pages(struct device *dev, unsigned long *user_pfn,
extern int vfio_unpin_pages(struct device *dev, unsigned long *user_pfn,
int npage);

+extern int vfio_dma_rw(struct vfio_group *group, dma_addr_t iova, void *data,
+ size_t len, bool write);
+
/* each type has independent events */
enum vfio_notify_type {
VFIO_IOMMU_NOTIFY = 0,
--
2.17.1