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.
>> 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 = {
>
