Re: [RFC v3 18/21] vfio-pci: Add a new VFIO_REGION_TYPE_NESTED region type

Alex Williamson
2019-01-11T23:58:45Z

On Tue, 8 Jan 2019 11:26:30 +0100
Eric Auger <eric.auger@redhat.com> wrote:

> This patch adds a new 64kB region aiming to report nested mode
> translation faults.
>
> The region contains a header with the size of the queue,
> the producer and consumer indices and then the actual
> fault queue data. The producer is updated by the kernel while
> the consumer is updated by the userspace.
>
> Signed-off-by: Eric Auger <eric.auger@redhat.com>
>
> ---
> ---
> drivers/vfio/pci/vfio_pci.c | 102 +++++++++++++++++++++++++++-
> drivers/vfio/pci/vfio_pci_private.h | 2 +
> include/uapi/linux/vfio.h | 15 ++++
> 3 files changed, 118 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c
> index ff60bd1ea587..2ba181ab2edd 100644
> --- a/drivers/vfio/pci/vfio_pci.c
> +++ b/drivers/vfio/pci/vfio_pci.c
> @@ -56,6 +56,11 @@ module_param(disable_idle_d3, bool, S_IRUGO | S_IWUSR);
> MODULE_PARM_DESC(disable_idle_d3,
> "Disable using the PCI D3 low power state for idle, unused devices");
>
> +#define VFIO_FAULT_REGION_SIZE 0x10000

Why 64K?

> +#define VFIO_FAULT_QUEUE_SIZE \
> + ((VFIO_FAULT_REGION_SIZE - sizeof(struct vfio_fault_region_header)) / \
> + sizeof(struct iommu_fault))
> +
> static inline bool vfio_vga_disabled(void)
> {
> #ifdef CONFIG_VFIO_PCI_VGA
> @@ -1226,6 +1231,100 @@ static const struct vfio_device_ops vfio_pci_ops = {
> static int vfio_pci_reflck_attach(struct vfio_pci_device *vdev);
> static void vfio_pci_reflck_put(struct vfio_pci_reflck *reflck);
>
> +static size_t
> +vfio_pci_dma_fault_rw(struct vfio_pci_device *vdev, char __user *buf,
> + size_t count, loff_t *ppos, bool iswrite)
> +{
> + unsigned int i = VFIO_PCI_OFFSET_TO_INDEX(*ppos) - VFIO_PCI_NUM_REGIONS;
> + void *base = vdev->region[i].data;
> + loff_t pos = *ppos & VFIO_PCI_OFFSET_MASK;
> +
> + if (pos >= vdev->region[i].size)
> + return -EINVAL;
> +
> + count = min(count, (size_t)(vdev->region[i].size - pos));
> +
> + if (copy_to_user(buf, base + pos, count))
> + return -EFAULT;
> +
> + *ppos += count;
> +
> + return count;
> +}
> +
> +static int vfio_pci_dma_fault_mmap(struct vfio_pci_device *vdev,
> + struct vfio_pci_region *region,
> + struct vm_area_struct *vma)
> +{
> + u64 phys_len, req_len, pgoff, req_start;
> + unsigned long long addr;
> + unsigned int index;
> +
> + index = vma->vm_pgoff >> (VFIO_PCI_OFFSET_SHIFT - PAGE_SHIFT);
> +
> + if (vma->vm_end < vma->vm_start)
> + return -EINVAL;
> + if ((vma->vm_flags & VM_SHARED) == 0)
> + return -EINVAL;
> +
> + phys_len = VFIO_FAULT_REGION_SIZE;
> +
> + req_len = vma->vm_end - vma->vm_start;
> + pgoff = vma->vm_pgoff &
> + ((1U << (VFIO_PCI_OFFSET_SHIFT - PAGE_SHIFT)) - 1);
> + req_start = pgoff << PAGE_SHIFT;
> +
> + if (req_start + req_len > phys_len)
> + return -EINVAL;
> +
> + addr = virt_to_phys(vdev->fault_region);
> + vma->vm_private_data = vdev;
> + vma->vm_pgoff = (addr >> PAGE_SHIFT) + pgoff;
> +
> + return remap_pfn_range(vma, vma->vm_start, vma->vm_pgoff,
> + req_len, vma->vm_page_prot);
> +}
> +
> +void vfio_pci_dma_fault_release(struct vfio_pci_device *vdev,
> + struct vfio_pci_region *region)
> +{
> +}
> +
> +static const struct vfio_pci_regops vfio_pci_dma_fault_regops = {
> + .rw = vfio_pci_dma_fault_rw,
> + .mmap = vfio_pci_dma_fault_mmap,
> + .release = vfio_pci_dma_fault_release,
> +};
> +
> +static int vfio_pci_init_dma_fault_region(struct vfio_pci_device *vdev)
> +{
> + u32 flags = VFIO_REGION_INFO_FLAG_READ | VFIO_REGION_INFO_FLAG_WRITE |
> + VFIO_REGION_INFO_FLAG_MMAP;
> + int ret;
> +
> + spin_lock_init(&vdev->fault_queue_lock);
> +
> + vdev->fault_region = kmalloc(VFIO_FAULT_REGION_SIZE, GFP_KERNEL);
> + if (!vdev->fault_region)
> + return -ENOMEM;
> +
> + ret = vfio_pci_register_dev_region(vdev,
> + VFIO_REGION_TYPE_NESTED,
> + VFIO_REGION_SUBTYPE_NESTED_FAULT_REGION,
> + &vfio_pci_dma_fault_regops, VFIO_FAULT_REGION_SIZE,
> + flags, vdev->fault_region);
> + if (ret) {
> + kfree(vdev->fault_region);
> + return ret;
> + }
> +
> + vdev->fault_region->header.prod = 0;
> + vdev->fault_region->header.cons = 0;
> + vdev->fault_region->header.reserved = 0;

Use kzalloc above or else we're leaking kernel memory to userspace
anyway.

> + vdev->fault_region->header.size = VFIO_FAULT_QUEUE_SIZE;
> + return 0;
> +}
> +
> static int vfio_pci_probe(struct pci_dev *pdev, const struct pci_device_id *id)
> {
> struct vfio_pci_device *vdev;
> @@ -1300,7 +1399,7 @@ static int vfio_pci_probe(struct pci_dev *pdev, const struct pci_device_id *id)
> pci_set_power_state(pdev, PCI_D3hot);
> }
>
> - return ret;
> + return vfio_pci_init_dma_fault_region(vdev);

Missing lots of cleanup should this fail. Why is this done on probe
anyway? This looks like something we'd do from vfio_pci_enable() and
therefore our release callback would free fault_region rather than what
we have below.

> }
>
> static void vfio_pci_remove(struct pci_dev *pdev)
> @@ -1315,6 +1414,7 @@ static void vfio_pci_remove(struct pci_dev *pdev)
>
> vfio_iommu_group_put(pdev->dev.iommu_group, &pdev->dev);
> kfree(vdev->region);
> + kfree(vdev->fault_region);
> mutex_destroy(&vdev->ioeventfds_lock);
> kfree(vdev);
>
> diff --git a/drivers/vfio/pci/vfio_pci_private.h b/drivers/vfio/pci/vfio_pci_private.h
> index 8c0009f00818..38b5d1764a26 100644
> --- a/drivers/vfio/pci/vfio_pci_private.h
> +++ b/drivers/vfio/pci/vfio_pci_private.h
> @@ -120,6 +120,8 @@ struct vfio_pci_device {
> int ioeventfds_nr;
> struct eventfd_ctx *err_trigger;
> struct eventfd_ctx *req_trigger;
> + spinlock_t fault_queue_lock;
> + struct vfio_fault_region *fault_region;
> struct list_head dummy_resources_list;
> struct mutex ioeventfds_lock;
> struct list_head ioeventfds_list;
> diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
> index 352e795a93c8..b78c2c62af6d 100644
> --- a/include/uapi/linux/vfio.h
> +++ b/include/uapi/linux/vfio.h
> @@ -307,6 +307,9 @@ struct vfio_region_info_cap_type {
> #define VFIO_REGION_TYPE_GFX (1)
> #define VFIO_REGION_SUBTYPE_GFX_EDID (1)
>
> +#define VFIO_REGION_TYPE_NESTED (2)
> +#define VFIO_REGION_SUBTYPE_NESTED_FAULT_REGION (1)
> +
> /**
> * struct vfio_region_gfx_edid - EDID region layout.
> *
> @@ -697,6 +700,18 @@ struct vfio_device_ioeventfd {
>
> #define VFIO_DEVICE_IOEVENTFD _IO(VFIO_TYPE, VFIO_BASE + 16)
>
> +struct vfio_fault_region_header {
> + __u32 size; /* Read-Only */
> + __u32 prod; /* Read-Only */

We can't really enforce read-only if it's mmap'd. I worry about
synchronization here too, perhaps there should be a ring offset such
that the ring can be in a separate page from the header and then sparse
mmap support can ensure that the user access is restricted. I also
wonder if there are other transports that make sense here, this almost
feels like a vhost sort of thing. Thanks,

Alex

> + __u32 cons;
> + __u32 reserved; /* must be 0 */
> +};
> +
> +struct vfio_fault_region {
> + struct vfio_fault_region_header header;
> + struct iommu_fault queue[0];
> +};
> +
> /* -------- API for Type1 VFIO IOMMU -------- */
>
> /**