Jérôme Glisse <jglisse@xxxxxxxxxx> writes:
> [ text/plain ]
> This patch add helper for device page fault. Thus helpers will fill
> the mirror page table using the CPU page table and synchronizing
> with any update to CPU page table.
>
> Changed since v1:
> - Add comment about directory lock.
>
> Changed since v2:
> - Check for mirror->hmm in hmm_mirror_fault()
>
> Changed since v3:
> - Adapt to HMM page table changes.
>
> Changed since v4:
> - Fix PROT_NONE, ie do not populate from protnone pte.
> - Fix huge pmd handling (start address may != pmd start address)
> - Fix missing entry case.
>
> Signed-off-by: Jérôme Glisse <jglisse@xxxxxxxxxx>
> Signed-off-by: Sherry Cheung <SCheung@xxxxxxxxxx>
> Signed-off-by: Subhash Gutti <sgutti@xxxxxxxxxx>
> Signed-off-by: Mark Hairgrove <mhairgrove@xxxxxxxxxx>
> Signed-off-by: John Hubbard <jhubbard@xxxxxxxxxx>
> Signed-off-by: Jatin Kumar <jakumar@xxxxxxxxxx>
> ---
....
....
+static int hmm_mirror_fault_hpmd(struct hmm_mirror *mirror,
> + struct hmm_event *event,
> + struct vm_area_struct *vma,
> + struct hmm_pt_iter *iter,
> + pmd_t *pmdp,
> + struct hmm_mirror_fault *mirror_fault,
> + unsigned long start,
> + unsigned long end)
> +{
> + struct page *page;
> + unsigned long addr, pfn;
> + unsigned flags = FOLL_TOUCH;
> + spinlock_t *ptl;
> + int ret;
> +
> + ptl = pmd_lock(mirror->hmm->mm, pmdp);
> + if (unlikely(!pmd_trans_huge(*pmdp))) {
> + spin_unlock(ptl);
> + return -EAGAIN;
> + }
> + flags |= event->etype == HMM_DEVICE_WFAULT ? FOLL_WRITE : 0;
> + page = follow_trans_huge_pmd(vma, start, pmdp, flags);
> + pfn = page_to_pfn(page);
> + spin_unlock(ptl);
> +
> + /* Just fault in the whole PMD. */
> + start &= PMD_MASK;
> + end = start + PMD_SIZE - 1;
> +
> + if (!pmd_write(*pmdp) && event->etype == HMM_DEVICE_WFAULT)
> + return -ENOENT;
> +
> + for (ret = 0, addr = start; !ret && addr < end;) {
> + unsigned long i, next = end;
> + dma_addr_t *hmm_pte;
> +
> + hmm_pte = hmm_pt_iter_populate(iter, addr, &next);
> + if (!hmm_pte)
> + return -ENOMEM;
> +
> + i = hmm_pt_index(&mirror->pt, addr, mirror->pt.llevel);
> +
> + /*
> + * The directory lock protect against concurrent clearing of
> + * page table bit flags. Exceptions being the dirty bit and
> + * the device driver private flags.
> + */
> + hmm_pt_iter_directory_lock(iter);
> + do {
> + if (!hmm_pte_test_valid_pfn(&hmm_pte[i])) {
> + hmm_pte[i] = hmm_pte_from_pfn(pfn);
> + hmm_pt_iter_directory_ref(iter);
I looked at that and it is actually
static inline void hmm_pt_iter_directory_ref(struct hmm_pt_iter *iter)
{
BUG_ON(!iter->ptd[iter->pt->llevel - 1]);
hmm_pt_directory_ref(iter->pt, iter->ptd[iter->pt->llevel - 1]);
}
static inline void hmm_pt_directory_ref(struct hmm_pt *pt,
struct page *ptd)
{
if (!atomic_inc_not_zero(&ptd->_mapcount))
/* Illegal this should not happen. */
BUG();
}
what is the mapcount update about ?
> + }
> + BUG_ON(hmm_pte_pfn(hmm_pte[i]) != pfn);
> + if (pmd_write(*pmdp))
> + hmm_pte_set_write(&hmm_pte[i]);
> + } while (addr += PAGE_SIZE, pfn++, i++, addr != next);
> + hmm_pt_iter_directory_unlock(iter);
> + mirror_fault->addr = addr;
> + }
> +
So we don't have huge page mapping in hmm page table ?
> + return 0;
> +}
> +
> +static int hmm_pte_hole(unsigned long addr,
> + unsigned long next,
> + struct mm_walk *walk)
> +{
> + return -ENOENT;
> +}
> +
-aneesh
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