X-Git-Url: https://gerrit.opnfv.org/gerrit/gitweb?a=blobdiff_plain;f=kernel%2Fmm%2Fgup.c;h=4b0b7e7d1136820790098312d148d663dd170441;hb=refs%2Fchanges%2F19%2F30119%2F1;hp=deafa2c91b362206b7ef56aec918509a9cc24dd2;hpb=c189ccac5702322ed843fe17057035b7222a59b6;p=kvmfornfv.git

diff --git a/kernel/mm/gup.c b/kernel/mm/gup.c
index deafa2c91..4b0b7e7d1 100644
--- a/kernel/mm/gup.c
+++ b/kernel/mm/gup.c
@@ -58,6 +58,16 @@ static int follow_pfn_pte(struct vm_area_struct *vma, unsigned long address,
 	return -EEXIST;
 }
 
+/*
+ * FOLL_FORCE can write to even unwritable pte's, but only
+ * after we've gone through a COW cycle and they are dirty.
+ */
+static inline bool can_follow_write_pte(pte_t pte, unsigned int flags)
+{
+	return pte_write(pte) ||
+		((flags & FOLL_FORCE) && (flags & FOLL_COW) && pte_dirty(pte));
+}
+
 static struct page *follow_page_pte(struct vm_area_struct *vma,
 		unsigned long address, pmd_t *pmd, unsigned int flags)
 {
@@ -92,7 +102,7 @@ retry:
 	}
 	if ((flags & FOLL_NUMA) && pte_protnone(pte))
 		goto no_page;
-	if ((flags & FOLL_WRITE) && !pte_write(pte)) {
+	if ((flags & FOLL_WRITE) && !can_follow_write_pte(pte, flags)) {
 		pte_unmap_unlock(ptep, ptl);
 		return NULL;
 	}
@@ -352,7 +362,7 @@ static int faultin_page(struct task_struct *tsk, struct vm_area_struct *vma,
 	 * reCOWed by userspace write).
 	 */
 	if ((ret & VM_FAULT_WRITE) && !(vma->vm_flags & VM_WRITE))
-		*flags &= ~FOLL_WRITE;
+	        *flags |= FOLL_COW;
 	return 0;
 }