On Tue, Oct 15, 2019 at 03:12:30PM -0300, Jason Gunthorpe wrote:
> From: Jason Gunthorpe <jgg@xxxxxxxxxxxx>
>
> hmm_mirror's handling of ranges does not use a sequence count which
> results in this bug:
>
> CPU0 CPU1
> hmm_range_wait_until_valid(range)
> valid == true
> hmm_range_fault(range)
> hmm_invalidate_range_start()
> range->valid = false
> hmm_invalidate_range_end()
> range->valid = true
> hmm_range_valid(range)
> valid == true
>
> Where the hmm_range_valid should not have succeeded.
>
> Adding the required sequence count would make it nearly identical to the
> new mmu_range_notifier. Instead replace the hmm_mirror stuff with
> mmu_range_notifier.
>
> Co-existence of the two APIs is the first step.
>
> Signed-off-by: Jason Gunthorpe <jgg@xxxxxxxxxxxx>
Reviewed-by: Jérôme Glisse <jglisse@xxxxxxxxxx>
> ---
> include/linux/hmm.h | 5 +++++
> mm/hmm.c | 25 +++++++++++++++++++------
> 2 files changed, 24 insertions(+), 6 deletions(-)
>
> diff --git a/include/linux/hmm.h b/include/linux/hmm.h
> index 3fec513b9c00f1..8ac1fd6a81af8f 100644
> --- a/include/linux/hmm.h
> +++ b/include/linux/hmm.h
> @@ -145,6 +145,9 @@ enum hmm_pfn_value_e {
> /*
> * struct hmm_range - track invalidation lock on virtual address range
> *
> + * @notifier: an optional mmu_range_notifier
> + * @notifier_seq: when notifier is used this is the result of
> + * mmu_range_read_begin()
> * @hmm: the core HMM structure this range is active against
> * @vma: the vm area struct for the range
> * @list: all range lock are on a list
> @@ -159,6 +162,8 @@ enum hmm_pfn_value_e {
> * @valid: pfns array did not change since it has been fill by an HMM function
> */
> struct hmm_range {
> + struct mmu_range_notifier *notifier;
> + unsigned long notifier_seq;
> struct hmm *hmm;
> struct list_head list;
> unsigned long start;
> diff --git a/mm/hmm.c b/mm/hmm.c
> index 902f5fa6bf93ad..22ac3595771feb 100644
> --- a/mm/hmm.c
> +++ b/mm/hmm.c
> @@ -852,6 +852,14 @@ void hmm_range_unregister(struct hmm_range *range)
> }
> EXPORT_SYMBOL(hmm_range_unregister);
>
> +static bool needs_retry(struct hmm_range *range)
> +{
> + if (range->notifier)
> + return mmu_range_check_retry(range->notifier,
> + range->notifier_seq);
> + return !range->valid;
> +}
> +
> static const struct mm_walk_ops hmm_walk_ops = {
> .pud_entry = hmm_vma_walk_pud,
> .pmd_entry = hmm_vma_walk_pmd,
> @@ -892,18 +900,23 @@ long hmm_range_fault(struct hmm_range *range, unsigned int flags)
> const unsigned long device_vma = VM_IO | VM_PFNMAP | VM_MIXEDMAP;
> unsigned long start = range->start, end;
> struct hmm_vma_walk hmm_vma_walk;
> - struct hmm *hmm = range->hmm;
> + struct mm_struct *mm;
> struct vm_area_struct *vma;
> int ret;
>
> - lockdep_assert_held(&hmm->mmu_notifier.mm->mmap_sem);
> + if (range->notifier)
> + mm = range->notifier->mm;
> + else
> + mm = range->hmm->mmu_notifier.mm;
> +
> + lockdep_assert_held(&mm->mmap_sem);
>
> do {
> /* If range is no longer valid force retry. */
> - if (!range->valid)
> + if (needs_retry(range))
> return -EBUSY;
>
> - vma = find_vma(hmm->mmu_notifier.mm, start);
> + vma = find_vma(mm, start);
> if (vma == NULL || (vma->vm_flags & device_vma))
> return -EFAULT;
>
> @@ -933,7 +946,7 @@ long hmm_range_fault(struct hmm_range *range, unsigned int flags)
> start = hmm_vma_walk.last;
>
> /* Keep trying while the range is valid. */
> - } while (ret == -EBUSY && range->valid);
> + } while (ret == -EBUSY && !needs_retry(range));
>
> if (ret) {
> unsigned long i;
> @@ -991,7 +1004,7 @@ long hmm_range_dma_map(struct hmm_range *range, struct device *device,
> continue;
>
> /* Check if range is being invalidated */
> - if (!range->valid) {
> + if (needs_retry(range)) {
> ret = -EBUSY;
> goto unmap;
> }
> --
> 2.23.0
>
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