| From | Jérôme Glisse <> | Subject | [PATCH v12 27/29] HMM: fork copy migrated memory into system memory for child process. | Date | Tue, 8 Mar 2016 15:43:20 -0500 |
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When forking if process being fork had any memory migrated to some device memory, we need to make a system copy for the child process. Latter patches can revisit this and use the same COW semantic for device memory.
Signed-off-by: Jérôme Glisse <jglisse@redhat.com> --- mm/hmm.c | 38 +++++++++++++++++++++++++++++++++++++- 1 file changed, 37 insertions(+), 1 deletion(-)
diff --git a/mm/hmm.c b/mm/hmm.c index 435e376..4dcd98f 100644 --- a/mm/hmm.c +++ b/mm/hmm.c @@ -483,7 +483,37 @@ int hmm_mm_fork(struct mm_struct *src_mm, unsigned long start, unsigned long end) { - return -ENOMEM; + unsigned long npages = (end - start) >> PAGE_SHIFT; + struct hmm_event event; + dma_addr_t *dst; + struct hmm *hmm; + pte_t *new_pte; + int ret; + + hmm = hmm_ref(src_mm->hmm); + if (!hmm) + return -EINVAL; + + + dst = kcalloc(npages, sizeof(*dst), GFP_KERNEL); + if (!dst) { + hmm_unref(hmm); + return -ENOMEM; + } + new_pte = kcalloc(npages, sizeof(*new_pte), GFP_KERNEL); + if (!new_pte) { + kfree(dst); + hmm_unref(hmm); + return -ENOMEM; + } + + hmm_event_init(&event, hmm, start, end, HMM_FORK); + ret = hmm_migrate_back(hmm, &event, dst_mm, dst_vma, new_pte, + dst, start, end); + hmm_unref(hmm); + kfree(new_pte); + kfree(dst); + return ret; } EXPORT_SYMBOL(hmm_mm_fork); @@ -665,6 +695,12 @@ static void hmm_mirror_update_pte(struct hmm_mirror *mirror, } if (hmm_pte_test_valid_dev(hmm_pte)) { + /* + * On fork device memory is duplicated so no need to write + * protect it. + */ + if (event->etype == HMM_FORK) + return; *hmm_pte &= event->pte_mask; if (!hmm_pte_test_valid_dev(hmm_pte)) hmm_pt_iter_directory_unref(iter); -- 2.4.3
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