Re: [PATCH V1 5/5] vfio: block during VA suspend

Alex Williamson
2021-01-08T21:34:01Z

On Tue, 5 Jan 2021 07:36:53 -0800
Steve Sistare <steven.sistare@oracle.com> wrote:

> Block translation of host virtual address while an iova range is suspended.
>
> Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
> ---
> drivers/vfio/vfio_iommu_type1.c | 48 ++++++++++++++++++++++++++++++++++++++---
> 1 file changed, 45 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
> index 2c164a6..8035b9a 100644
> --- a/drivers/vfio/vfio_iommu_type1.c
> +++ b/drivers/vfio/vfio_iommu_type1.c
> @@ -31,6 +31,8 @@
> #include <linux/rbtree.h>
> #include <linux/sched/signal.h>
> #include <linux/sched/mm.h>
> +#include <linux/delay.h>
> +#include <linux/kthread.h>
> #include <linux/slab.h>
> #include <linux/uaccess.h>
> #include <linux/vfio.h>
> @@ -484,6 +486,34 @@ static int vaddr_get_pfn(struct mm_struct *mm, unsigned long vaddr,
> return ret;
> }
>
> +static bool vfio_iommu_contained(struct vfio_iommu *iommu)
> +{
> + struct vfio_domain *domain = iommu->external_domain;
> + struct vfio_group *group;
> +
> + if (!domain)
> + domain = list_first_entry(&iommu->domain_list,
> + struct vfio_domain, next);
> +
> + group = list_first_entry(&domain->group_list, struct vfio_group, next);
> + return vfio_iommu_group_contained(group->iommu_group);
> +}

This seems really backwards for a vfio iommu backend to ask vfio-core
whether its internal object is active.

> +
> +
> +bool vfio_vaddr_valid(struct vfio_iommu *iommu, struct vfio_dma *dma)
> +{
> + while (dma->suspended) {
> + mutex_unlock(&iommu->lock);
> + msleep_interruptible(10);
> + mutex_lock(&iommu->lock);
> + if (kthread_should_stop() || !vfio_iommu_contained(iommu) ||
> + fatal_signal_pending(current)) {
> + return false;
> + }
> + }
> + return true;
> +}
> +
> /*
> * Attempt to pin pages. We really don't want to track all the pfns and
> * the iommu can only map chunks of consecutive pfns anyway, so get the
> @@ -690,6 +720,11 @@ static int vfio_iommu_type1_pin_pages(void *iommu_data,
> continue;
> }
>
> + if (!vfio_vaddr_valid(iommu, dma)) {
> + ret = -EFAULT;
> + goto pin_unwind;
> + }

This could have dropped iommu->lock, we have no basis to believe our
vfio_dma object is still valid. Also this is called with an elevated
reference to the container, so we theoretically should not need to test
whether the iommu is still contained.

> +
> remote_vaddr = dma->vaddr + (iova - dma->iova);
> ret = vfio_pin_page_external(dma, remote_vaddr, &phys_pfn[i],
> do_accounting);
> @@ -1514,12 +1549,16 @@ static int vfio_iommu_replay(struct vfio_iommu *iommu,
> i += PAGE_SIZE;
> }
> } else {
> - unsigned long pfn;
> - unsigned long vaddr = dma->vaddr +
> - (iova - dma->iova);
> + unsigned long pfn, vaddr;
> size_t n = dma->iova + dma->size - iova;
> long npage;
>
> + if (!vfio_vaddr_valid(iommu, dma)) {
> + ret = -EFAULT;
> + goto unwind;
> + }

This one is even scarier, do we have any basis to assume either object
is still valid after iommu->lock is released? We can only get here if
we're attaching a group to the iommu with suspended vfio_dmas. Do we
need to allow that? It seems we could -EAGAIN and let the user figure
out that they can't attach a group while mappings have invalid vaddrs.

> + vaddr = dma->vaddr + (iova - dma->iova);
> +
> npage = vfio_pin_pages_remote(dma, vaddr,
> n >> PAGE_SHIFT,
> &pfn, limit);
> @@ -2965,6 +3004,9 @@ static int vfio_iommu_type1_dma_rw_chunk(struct vfio_iommu *iommu,
> if (count > dma->size - offset)
> count = dma->size - offset;
>
> + if (!vfio_vaddr_valid(iommu, dma))

Same as the pinning path, this should hold a container user reference
but we cannot assume our vfio_dma object is valid if we've released the
lock. Thanks,

Alex

> + goto out;
> +
> vaddr = dma->vaddr + offset;
>
> if (write) {