Re: [PATCH 5/6] vduse: Support registering userspace memory for IOTLB

From: Michael S. Tsirkin
Date: Wed Jun 29 2022 - 05:54:36 EST

On Wed, Jun 29, 2022 at 05:26:04PM +0800, Yongji Xie wrote:
> On Wed, Jun 29, 2022 at 4:43 PM Michael S. Tsirkin <mst@xxxxxxxxxx> wrote:
> >
> > On Wed, Jun 29, 2022 at 04:25:40PM +0800, Xie Yongji wrote:
> > > Introduce two ioctls: VDUSE_IOTLB_REG_UMEM and
> > > VDUSE_IOTLB_DEREG_UMEM to support registering
> > > and de-registering userspace memory for IOTLB
> > > in virtio-vdpa case.
> > >
> > > Now it only supports registering userspace memory
> > > for IOTLB as bounce buffer.
> > >
> > > Signed-off-by: Xie Yongji <xieyongji@xxxxxxxxxxxxx>
> > > ---
> > > drivers/vdpa/vdpa_user/vduse_dev.c | 138 +++++++++++++++++++++++++++++
> > > include/uapi/linux/vduse.h | 28 ++++++
> > > 2 files changed, 166 insertions(+)
> > >
> > > diff --git a/drivers/vdpa/vdpa_user/vduse_dev.c b/drivers/vdpa/vdpa_user/vduse_dev.c
> > > index c47a5d9765cf..7b2ea7612da9 100644
> > > --- a/drivers/vdpa/vdpa_user/vduse_dev.c
> > > +++ b/drivers/vdpa/vdpa_user/vduse_dev.c
> > > @@ -21,6 +21,7 @@
> > > #include <linux/uio.h>
> > > #include <linux/vdpa.h>
> > > #include <linux/nospec.h>
> > > +#include <linux/sched/mm.h>
> > > #include <uapi/linux/vduse.h>
> > > #include <uapi/linux/vdpa.h>
> > > #include <uapi/linux/virtio_config.h>
> > > @@ -64,6 +65,13 @@ struct vduse_vdpa {
> > > struct vduse_dev *dev;
> > > };
> > >
> > > +struct vduse_iotlb_mem {
> > > + unsigned long iova;
> > > + unsigned long npages;
> > > + struct page **pages;
> > > + struct mm_struct *mm;
> > > +};
> > > +
> > > struct vduse_dev {
> > > struct vduse_vdpa *vdev;
> > > struct device *dev;
> > > @@ -95,6 +103,8 @@ struct vduse_dev {
> > > u8 status;
> > > u32 vq_num;
> > > u32 vq_align;
> > > + struct vduse_iotlb_mem *iotlb_mem;
> > > + struct mutex mem_lock;
> > > };
> > >
> > > struct vduse_dev_msg {
> > > @@ -917,6 +927,100 @@ static int vduse_dev_queue_irq_work(struct vduse_dev *dev,
> > > return ret;
> > > }
> > >
> > > +static int vduse_dev_dereg_iotlb_mem(struct vduse_dev *dev,
> > > + u64 iova, u64 size)
> > > +{
> > > + int ret;
> > > +
> > > + mutex_lock(&dev->mem_lock);
> > > + ret = -ENOENT;
> > > + if (!dev->iotlb_mem)
> > > + goto unlock;
> > > +
> > > + ret = -EINVAL;
> > > + if (dev->iotlb_mem->iova != iova || size != dev->domain->bounce_size)
> > > + goto unlock;
> > > +
> > > + vduse_domain_remove_user_bounce_pages(dev->domain);
> > > + unpin_user_pages(dev->iotlb_mem->pages, dev->iotlb_mem->npages);
> >
> > I notice you don't mark the pages dirty. This is going to be a problem.
> >
>
> Thanks for pointing out this, I will use unpin_user_pages_dirty_lock() instead.
>
> > > + atomic64_sub(dev->iotlb_mem->npages, &dev->iotlb_mem->mm->pinned_vm);
> > > + mmdrop(dev->iotlb_mem->mm);
> > > + vfree(dev->iotlb_mem->pages);
> > > + kfree(dev->iotlb_mem);
> > > + dev->iotlb_mem = NULL;
> > > + ret = 0;
> > > +unlock:
> > > + mutex_unlock(&dev->mem_lock);
> > > + return ret;
> > > +}
> > > +
> > > +static int vduse_dev_reg_iotlb_mem(struct vduse_dev *dev,
> > > + u64 iova, u64 uaddr, u64 size)
> > > +{
> > > + struct page **page_list = NULL;
> > > + struct vduse_iotlb_mem *mem = NULL;
> > > + long pinned = 0;
> > > + unsigned long npages, lock_limit;
> > > + int ret;
> > > +
> > > + if (size != dev->domain->bounce_size ||
> > > + iova != 0 || uaddr & ~PAGE_MASK)
> > > + return -EINVAL;
> > > +
> > > + mutex_lock(&dev->mem_lock);
> > > + ret = -EEXIST;
> > > + if (dev->iotlb_mem)
> > > + goto unlock;
> > > +
> > > + ret = -ENOMEM;
> > > + npages = size >> PAGE_SHIFT;
> > > + page_list = vmalloc(array_size(npages,
> > > + sizeof(struct page *)));
> >
> > Is this basically trying to do a vmalloc with userspace-controlled size?
> > That's an easy DOS vector.
> >
>
> We already checked the size before. The size must equal to (64MB >>
> PAGE_SHIFT) now.

That's not a small amount. Can this be accounted e.g. through cgroups at least?

> > > + mem = kzalloc(sizeof(*mem), GFP_KERNEL);
> > > + if (!page_list || !mem)
> > > + goto unlock;
> > > +
> > > + mmap_read_lock(current->mm);
> > > +
> > > + lock_limit = PFN_DOWN(rlimit(RLIMIT_MEMLOCK));
> > > + if (npages + atomic64_read(&current->mm->pinned_vm) > lock_limit)
> > > + goto out;
> > > +
> > > + pinned = pin_user_pages(uaddr, npages, FOLL_LONGTERM | FOLL_WRITE,
> > > + page_list, NULL);
> > > + if (pinned != npages) {
> > > + ret = pinned < 0 ? pinned : -ENOMEM;
> > > + goto out;
> > > + }
> >
> >
> > This is a popular approach but it's problematic if multiple
> > devices try to pin the same page.
>
> Do you mean the data would be corrupted if multiple devices use the
> same page as bounce buffer? This is indeed a problem.

No i mean you decrement the lock twice. Question is can two bounce
buffers share a page?

> > Can this happen here?
> >
>
> I think we can't prevent this case now. I will do it in v2.
>
> > > +
> > > + ret = vduse_domain_add_user_bounce_pages(dev->domain,
> > > + page_list, pinned);
> > > + if (ret)
> > > + goto out;
> > > +
> > > + atomic64_add(npages, &current->mm->pinned_vm);
> > > +
> > > + mem->pages = page_list;
> > > + mem->npages = pinned;
> > > + mem->iova = iova;
> > > + mem->mm = current->mm;
> > > + mmgrab(current->mm);
> > > +
> > > + dev->iotlb_mem = mem;
> > > +out:
> > > + if (ret && pinned > 0)
> > > + unpin_user_pages(page_list, pinned);
> > > +
> > > + mmap_read_unlock(current->mm);
> > > +unlock:
> > > + if (ret) {
> > > + vfree(page_list);
> > > + kfree(mem);
> > > + }
> > > + mutex_unlock(&dev->mem_lock);
> > > + return ret;
> > > +}
> > > +
> > > static long vduse_dev_ioctl(struct file *file, unsigned int cmd,
> > > unsigned long arg)
> > > {
> > > @@ -943,6 +1047,16 @@ static long vduse_dev_ioctl(struct file *file, unsigned int cmd,
> > > if (entry.start > entry.last)
> > > break;
> > >
> > > + if (domain->bounce_map && dev->iotlb_mem) {
> > > + ret = -EEXIST;
> > > + if (entry.start >= 0 &&
> > > + entry.last < domain->bounce_size)
> > > + break;
> > > +
> > > + if (entry.start < domain->bounce_size)
> > > + entry.start = domain->bounce_size;
> > > + }
> > > +
> > > spin_lock(&domain->iotlb_lock);
> > > map = vhost_iotlb_itree_first(domain->iotlb,
> > > entry.start, entry.last);
> > > @@ -1102,6 +1216,28 @@ static long vduse_dev_ioctl(struct file *file, unsigned int cmd,
> > > ret = 0;
> > > break;
> > > }
> > > + case VDUSE_IOTLB_REG_UMEM: {
> > > + struct vduse_iotlb_umem umem;
> > > +
> > > + ret = -EFAULT;
> > > + if (copy_from_user(&umem, argp, sizeof(umem)))
> > > + break;
> > > +
> > > + ret = vduse_dev_reg_iotlb_mem(dev, umem.iova,
> > > + umem.uaddr, umem.size);
> > > + break;
> > > + }
> > > + case VDUSE_IOTLB_DEREG_UMEM: {
> > > + struct vduse_iotlb_umem umem;
> > > +
> > > + ret = -EFAULT;
> > > + if (copy_from_user(&umem, argp, sizeof(umem)))
> > > + break;
> > > +
> > > + ret = vduse_dev_dereg_iotlb_mem(dev, umem.iova,
> > > + umem.size);
> > > + break;
> > > + }
> > > default:
> > > ret = -ENOIOCTLCMD;
> > > break;
> > > @@ -1114,6 +1250,7 @@ static int vduse_dev_release(struct inode *inode, struct file *file)
> > > {
> > > struct vduse_dev *dev = file->private_data;
> > >
> > > + vduse_dev_dereg_iotlb_mem(dev, 0, dev->domain->bounce_size);
> > > spin_lock(&dev->msg_lock);
> > > /* Make sure the inflight messages can processed after reconncection */
> > > list_splice_init(&dev->recv_list, &dev->send_list);
> > > @@ -1176,6 +1313,7 @@ static struct vduse_dev *vduse_dev_create(void)
> > > return NULL;
> > >
> > > mutex_init(&dev->lock);
> > > + mutex_init(&dev->mem_lock);
> > > spin_lock_init(&dev->msg_lock);
> > > INIT_LIST_HEAD(&dev->send_list);
> > > INIT_LIST_HEAD(&dev->recv_list);
> > > diff --git a/include/uapi/linux/vduse.h b/include/uapi/linux/vduse.h
> > > index c201b7a77c2c..1b17391e228f 100644
> > > --- a/include/uapi/linux/vduse.h
> > > +++ b/include/uapi/linux/vduse.h
> > > @@ -227,6 +227,34 @@ struct vduse_iotlb_info {
> > > /* Get IOTLB information, e.g. bounce buffer size */
> > > #define VDUSE_IOTLB_GET_INFO _IOR(VDUSE_BASE, 0x18, struct vduse_iotlb_info)
> > >
> > > +/**
> > > + * struct vduse_iotlb_umem - userspace memory configuration
> > > + * @uaddr: start address of userspace memory, it must be aligned to page size
> > > + * @iova: IOVA of userspace memory, it must be equal to bounce iova returned
> > > + * by VDUSE_IOTLB_GET_INFO now
> > > + * @size: size of userspace memory, it must be equal to bounce size returned
> > > + * by VDUSE_IOTLB_GET_INFO now
> > > + * @reserved: for future use, needs to be initialized to zero
> >
> > You should check that it's 0 in that case, otherwise userspace
> > will conveniently forget.
> >
>
> OK, I will fix it.
>
> Thanks,
> Yongji