vfio: introduce vfio_dma_rw to read/write a range of IOVAs

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>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>

diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c
index 97b972b..6997f71 100644 (file)
--- a/drivers/vfio/vfio.c
+++ b/drivers/vfio/vfio.c
@@ -1999,6 +1999,55 @@ err_unpin_pages:
 }
 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 from/into 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
+ * @user_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 user_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,
+                                         user_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 a177bf2..9fdfae1 100644 (file)
--- 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>
@@ -2305,6 +2306,80 @@ static int vfio_iommu_type1_unregister_notifier(void *iommu_data,
        return blocking_notifier_chain_unregister(&iommu->notifier, nb);
 }
 
+static int vfio_iommu_type1_dma_rw_chunk(struct vfio_iommu *iommu,
+                                        dma_addr_t user_iova, void *data,
+                                        size_t count, bool write,
+                                        size_t *copied)
+{
+       struct mm_struct *mm;
+       unsigned long vaddr;
+       struct vfio_dma *dma;
+       bool kthread = current->mm == NULL;
+       size_t offset;
+
+       *copied = 0;
+
+       dma = vfio_find_dma(iommu, user_iova, 1);
+       if (!dma)
+               return -EINVAL;
+
+       if ((write && !(dma->prot & IOMMU_WRITE)) ||
+                       !(dma->prot & IOMMU_READ))
+               return -EPERM;
+
+       mm = get_task_mm(dma->task);
+
+       if (!mm)
+               return -EPERM;
+
+       if (kthread)
+               use_mm(mm);
+       else if (current->mm != mm)
+               goto out;
+
+       offset = user_iova - dma->iova;
+
+       if (count > dma->size - offset)
+               count = dma->size - offset;
+
+       vaddr = dma->vaddr + offset;
+
+       if (write)
+               *copied = __copy_to_user((void __user *)vaddr, data,
+                                        count) ? 0 : count;
+       else
+               *copied = __copy_from_user(data, (void __user *)vaddr,
+                                          count) ? 0 : count;
+       if (kthread)
+               unuse_mm(mm);
+out:
+       mmput(mm);
+       return *copied ? 0 : -EFAULT;
+}
+
+static int vfio_iommu_type1_dma_rw(void *iommu_data, dma_addr_t user_iova,
+                                  void *data, size_t count, bool write)
+{
+       struct vfio_iommu *iommu = iommu_data;
+       int ret = 0;
+       size_t done;
+
+       mutex_lock(&iommu->lock);
+       while (count > 0) {
+               ret = vfio_iommu_type1_dma_rw_chunk(iommu, user_iova, data,
+                                                   count, write, &done);
+               if (ret)
+                       break;
+
+               count -= done;
+               data += done;
+               user_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,
@@ -2317,6 +2392,7 @@ 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 fb71e0a..34b2fdf 100644 (file)
--- 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 user_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 user_iova,
+                      void *data, size_t len, bool write);
+
 /* each type has independent events */
 enum vfio_notify_type {
        VFIO_IOMMU_NOTIFY = 0,