On Wed, 27 Jan 2021 18:25:13 -0500
Steven Sistare <steven.sistare@xxxxxxxxxx> wrote:
> On 1/22/2021 5:59 PM, Alex Williamson wrote:
> > On Tue, 19 Jan 2021 09:48:29 -0800
> > Steve Sistare <steven.sistare@xxxxxxxxxx> wrote:
> >
> >> Block translation of host virtual address while an iova range has an
> >> invalid vaddr.
> >>
> >> Signed-off-by: Steve Sistare <steven.sistare@xxxxxxxxxx>
> >> ---
> >> drivers/vfio/vfio_iommu_type1.c | 83 +++++++++++++++++++++++++++++++++++++----
> >> 1 file changed, 76 insertions(+), 7 deletions(-)
> >>
> >> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
> >> index 0167996..c97573a 100644
> >> --- a/drivers/vfio/vfio_iommu_type1.c
> >> +++ b/drivers/vfio/vfio_iommu_type1.c
> >> @@ -31,6 +31,7 @@
> >> #include <linux/rbtree.h>
> >> #include <linux/sched/signal.h>
> >> #include <linux/sched/mm.h>
> >> +#include <linux/kthread.h>
> >> #include <linux/slab.h>
> >> #include <linux/uaccess.h>
> >> #include <linux/vfio.h>
> >> @@ -75,6 +76,7 @@ struct vfio_iommu {
> >> bool dirty_page_tracking;
> >> bool pinned_page_dirty_scope;
> >> bool controlled;
> >> + wait_queue_head_t vaddr_wait;
> >> };
> >>
> >> struct vfio_domain {
> >> @@ -145,6 +147,8 @@ struct vfio_regions {
> >> #define DIRTY_BITMAP_PAGES_MAX ((u64)INT_MAX)
> >> #define DIRTY_BITMAP_SIZE_MAX DIRTY_BITMAP_BYTES(DIRTY_BITMAP_PAGES_MAX)
> >>
> >> +#define WAITED 1
> >> +
> >> static int put_pfn(unsigned long pfn, int prot);
> >>
> >> static struct vfio_group *vfio_iommu_find_iommu_group(struct vfio_iommu *iommu,
> >> @@ -505,6 +509,52 @@ static int vaddr_get_pfn(struct mm_struct *mm, unsigned long vaddr,
> >> }
> >>
> >> /*
> >> + * Wait for vaddr of *dma_p to become valid. iommu lock is dropped if the task
> >> + * waits, but is re-locked on return. If the task waits, then return an updated
> >> + * dma struct in *dma_p. Return 0 on success with no waiting, 1 on success if
> >
> > s/1/WAITED/
>
> OK, but the WAITED state will not need to be returned in the new scheme below.
>
> >> + * waited, and -errno on error.
> >> + */
> >> +static int vfio_vaddr_wait(struct vfio_iommu *iommu, struct vfio_dma **dma_p)
> >> +{
> >> + struct vfio_dma *dma = *dma_p;
> >> + unsigned long iova = dma->iova;
> >> + size_t size = dma->size;
> >> + int ret = 0;
> >> + DEFINE_WAIT(wait);
> >> +
> >> + while (!dma->vaddr_valid) {
> >> + ret = WAITED;
> >> + prepare_to_wait(&iommu->vaddr_wait, &wait, TASK_KILLABLE);
> >> + mutex_unlock(&iommu->lock);
> >> + schedule();
> >> + mutex_lock(&iommu->lock);
> >> + finish_wait(&iommu->vaddr_wait, &wait);
> >> + if (kthread_should_stop() || !iommu->controlled ||
> >> + fatal_signal_pending(current)) {
> >> + return -EFAULT;
> >> + }
> >> + *dma_p = dma = vfio_find_dma(iommu, iova, size);
> >> + if (!dma)
> >> + return -EINVAL;
> >> + }
> >> + return ret;
> >> +}
> >> +
> >> +/*
> >> + * Find dma struct and wait for its vaddr to be valid. iommu lock is dropped
> >> + * if the task waits, but is re-locked on return. Return result in *dma_p.
> >> + * Return 0 on success, 1 on success if waited, and -errno on error.
> >> + */
> >> +static int vfio_find_vaddr(struct vfio_iommu *iommu, dma_addr_t start,
> >> + size_t size, struct vfio_dma **dma_p)
> >
> > more of a vfio_find_dma_valid()
>
> I will slightly modify and rename this with the new scheme I describe below.
>
> >> +{
> >> + *dma_p = vfio_find_dma(iommu, start, size);
> >> + if (!*dma_p)
> >> + return -EINVAL;
> >> + return vfio_vaddr_wait(iommu, dma_p);
> >> +}
> >> +
> >> +/*
> >> * 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
> >> * first page and all consecutive pages with the same locking.
> >> @@ -693,11 +743,11 @@ static int vfio_iommu_type1_pin_pages(void *iommu_data,
> >> struct vfio_pfn *vpfn;
> >>
> >> iova = user_pfn[i] << PAGE_SHIFT;
> >> - dma = vfio_find_dma(iommu, iova, PAGE_SIZE);
> >> - if (!dma) {
> >> - ret = -EINVAL;
> >> + ret = vfio_find_vaddr(iommu, iova, PAGE_SIZE, &dma);
> >> + if (ret < 0)
> >> goto pin_unwind;
> >> - }
> >> + else if (ret == WAITED)
> >> + do_accounting = !IS_IOMMU_CAP_DOMAIN_IN_CONTAINER(iommu);
> >
> > We're iterating through an array of pfns to provide translations, once
> > we've released the lock it's not just the current one that could be
> > invalid. I'm afraid we need to unwind and try again, but I think it's
> > actually worse than that because if we've marked pages within a
> > vfio_dma's pfn_list as pinned, then during the locking gap it gets
> > unmapped, the unmap path will call the unmap notifier chain to release
> > the page that the vendor driver doesn't have yet. Yikes!
>
> Yikes indeed. The fix is easy, though. I will maintain a count in vfio_iommu of
> vfio_dma objects with invalid vaddr's, modified and tested while holding the lock,
> provide a function to wait for the count to become 0, and call that function at the
> start of vfio_iommu_type1_pin_pages and vfio_iommu_replay. I will use iommu->vaddr_wait
> for wait and wake.
I prefer the overhead of this, but the resulting behavior seems pretty
non-intuitive. Any invalidated vaddr blocks all vaddr use cases, which
almost suggests the unmap _VADDR flag should only be allowed with the
_ALL flag, but then the map _VADDR flag can only be per mapping, which
would make accounting and recovering from _VADDR + _ALL pretty
complicated. Thanks,
Alex
> >> if ((dma->prot & prot) != prot) {
> >> ret = -EPERM;
> >> @@ -1496,6 +1546,22 @@ static int vfio_iommu_replay(struct vfio_iommu *iommu,
> >> unsigned long limit = rlimit(RLIMIT_MEMLOCK) >> PAGE_SHIFT;
> >> int ret;
> >>
> >> + /*
> >> + * Wait for all vaddr to be valid so they can be used in the main loop.
> >> + * If we do wait, the lock was dropped and re-taken, so start over to
> >> + * ensure the dma list is consistent.
> >> + */
> >> +again:
> >> + for (n = rb_first(&iommu->dma_list); n; n = rb_next(n)) {
> >> + struct vfio_dma *dma = rb_entry(n, struct vfio_dma, node);
> >> +
> >> + ret = vfio_vaddr_wait(iommu, &dma);
> >> + if (ret < 0)
> >> + return ret;
> >> + else if (ret == WAITED)
> >> + goto again;
> >> + }
> >
> > This "do nothing until all the vaddrs are valid" approach could work
> > above too, but gosh is that a lot of cache unfriendly work for a rare
> > invalidation. Thanks,
>
> The new wait function described above is fast in the common case, just a check that
> the invalid vaddr count is 0.
>
> - Steve
>
> >> +
> >> /* Arbitrarily pick the first domain in the list for lookups */
> >> if (!list_empty(&iommu->domain_list))
> >> d = list_first_entry(&iommu->domain_list,
> >> @@ -2522,6 +2588,7 @@ static void *vfio_iommu_type1_open(unsigned long arg)
> >> iommu->controlled = true;
> >> mutex_init(&iommu->lock);
> >> BLOCKING_INIT_NOTIFIER_HEAD(&iommu->notifier);
> >> + init_waitqueue_head(&iommu->vaddr_wait);
> >>
> >> return iommu;
> >> }
> >> @@ -2972,12 +3039,13 @@ static int vfio_iommu_type1_dma_rw_chunk(struct vfio_iommu *iommu,
> >> struct vfio_dma *dma;
> >> bool kthread = current->mm == NULL;
> >> size_t offset;
> >> + int ret;
> >>
> >> *copied = 0;
> >>
> >> - dma = vfio_find_dma(iommu, user_iova, 1);
> >> - if (!dma)
> >> - return -EINVAL;
> >> + ret = vfio_find_vaddr(iommu, user_iova, 1, &dma);
> >> + if (ret < 0)
> >> + return ret;
> >>
> >> if ((write && !(dma->prot & IOMMU_WRITE)) ||
> >> !(dma->prot & IOMMU_READ))
> >> @@ -3055,6 +3123,7 @@ static void vfio_iommu_type1_notify(void *iommu_data, unsigned int event,
> >> mutex_lock(&iommu->lock);
> >> iommu->controlled = false;
> >> mutex_unlock(&iommu->lock);
> >> + wake_up_all(&iommu->vaddr_wait);
> >> }
> >>
> >> static const struct vfio_iommu_driver_ops vfio_iommu_driver_ops_type1 = {
> >
>
