Re: [RFC PATCH v4 06/10] VFIO_PLATFORM: Read and write support for the device fd

Alex Williamson
2014-02-10T22:45:51Z

On Sat, 2014-02-08 at 18:29 +0100, Antonios Motakis wrote:
> VFIO returns a file descriptor which we can use to manipulate the memory
> regions of the device. Since some memory regions we cannot mmap due to
> security concerns, we also allow to read and write to this file descriptor
> directly.
>
> Signed-off-by: Antonios Motakis <a.motakis@virtualopensystems.com>
> Tested-by: Alvise Rigo <a.rigo@virtualopensystems.com>
> ---
> drivers/vfio/platform/vfio_platform.c | 128 +++++++++++++++++++++++++++++++++-
> 1 file changed, 125 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/vfio/platform/vfio_platform.c b/drivers/vfio/platform/vfio_platform.c
> index f7db5c0..ee96078 100644
> --- a/drivers/vfio/platform/vfio_platform.c
> +++ b/drivers/vfio/platform/vfio_platform.c
> @@ -55,7 +55,8 @@ static int vfio_platform_regions_init(struct vfio_platform_device *vdev)
>
> region.addr = res->start;
> region.size = resource_size(res);
> - region.flags = 0;
> + region.flags = VFIO_REGION_INFO_FLAG_READ
> + | VFIO_REGION_INFO_FLAG_WRITE;
>
> vdev->region[i] = region;
> }
> @@ -150,13 +151,134 @@ static long vfio_platform_ioctl(void *device_data,
> static ssize_t vfio_platform_read(void *device_data, char __user *buf,
> size_t count, loff_t *ppos)
> {
> - return 0;
> + struct vfio_platform_device *vdev = device_data;
> + unsigned int *io;
> + int i;
> +
> + for (i = 0; i < vdev->num_regions; i++) {
> + struct vfio_platform_region region = vdev->region[i];
> + unsigned int done = 0;
> + loff_t off;
> +
> + if ((*ppos < region.addr)
> + || (*ppos + count - 1) >= (region.addr + region.size))
> + continue;

Perhaps there's something to be said for vfio-pci's use of fixed offsets
to have a direct offset to index lookup.

> +
> + io = ioremap_nocache(region.addr, region.size);

This must incur some overhead per access.

> +
> + off = *ppos - region.addr;
> +
> + while (count) {
> + size_t filled;
> +
> + if (count >= 4 && !(off % 4)) {
> + u32 val;
> +
> + val = ioread32(io + off);
> + if (copy_to_user(buf, &val, 4))
> + goto err;

For vfio-pci we've decided that these interfaces are always little
endian, have you considered whether it makes sense to do something
similar here? Thanks,

Alex

> +
> + filled = 4;
> + } else if (count >= 2 && !(off % 2)) {
> + u16 val;
> +
> + val = ioread16(io + off);
> + if (copy_to_user(buf, &val, 2))
> + goto err;
> +
> + filled = 2;
> + } else {
> + u8 val;
> +
> + val = ioread8(io + off);
> + if (copy_to_user(buf, &val, 1))
> + goto err;
> +
> + filled = 1;
> + }
> +
> +
> + count -= filled;
> + done += filled;
> + off += filled;
> + buf += filled;
> + }
> +
> + iounmap(io);
> + return done;
> + }
> +
> + return -EFAULT;
> +
> +err:
> + iounmap(io);
> + return -EFAULT;
> }
>
> static ssize_t vfio_platform_write(void *device_data, const char __user *buf,
> size_t count, loff_t *ppos)
> {
> - return 0;
> + struct vfio_platform_device *vdev = device_data;
> + unsigned int *io;
> + int i;
> +
> + for (i = 0; i < vdev->num_regions; i++) {
> + struct vfio_platform_region region = vdev->region[i];
> + unsigned int done = 0;
> + loff_t off;
> +
> + if ((*ppos < region.addr)
> + || (*ppos + count - 1) >= (region.addr + region.size))
> + continue;
> +
> + io = ioremap_nocache(region.addr, region.size);
> +
> + off = *ppos - region.addr;
> +
> + while (count) {
> + size_t filled;
> +
> + if (count >= 4 && !(off % 4)) {
> + u32 val;
> +
> + if (copy_from_user(&val, buf, 4))
> + goto err;
> + iowrite32(val, io + off);
> +
> + filled = 4;
> + } else if (count >= 2 && !(off % 2)) {
> + u16 val;
> +
> + if (copy_from_user(&val, buf, 2))
> + goto err;
> + iowrite16(val, io + off);
> +
> + filled = 2;
> + } else {
> + u8 val;
> +
> + if (copy_from_user(&val, buf, 1))
> + goto err;
> + iowrite8(val, io + off);
> +
> + filled = 1;
> + }
> +
> + count -= filled;
> + done += filled;
> + off += filled;
> + buf += filled;
> + }
> +
> + iounmap(io);
> + return done;
> + }
> +
> + return -EINVAL;
> +
> +err:
> + iounmap(io);
> + return -EFAULT;
> }
>
> static int vfio_platform_mmap(void *device_data, struct vm_area_struct *vma)