[PATCH 2/3] mm/memory.c: Update local TLB if PTE entry exists

[Bibo Mao]

If there are two threads hitting page fault at the same page,
one thread updates PTE entry and local TLB, the other can
update local tlb also, rather than give up and do page fault
again.
---
Change in V2:
- separate tlb update and add pte readable privilege into two patches

Signed-off-by: Bibo Mao <maobibo@xxxxxxxxxxx>
---
 mm/memory.c | 44 +++++++++++++++++++++++++++-----------------
 1 file changed, 27 insertions(+), 17 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index f703fe8..57748de 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1770,8 +1770,8 @@ static vm_fault_t insert_pfn(struct vm_area_struct *vma, unsigned long addr,
 			}
 			entry = pte_mkyoung(*pte);
 			entry = maybe_mkwrite(pte_mkdirty(entry), vma);
-			if (ptep_set_access_flags(vma, addr, pte, entry, 1))
-				update_mmu_cache(vma, addr, pte);
+			ptep_set_access_flags(vma, addr, pte, entry, 1);
+			update_mmu_cache(vma, addr, pte);
 		}
 		goto out_unlock;
 	}
@@ -2436,17 +2436,16 @@ static inline bool cow_user_page(struct page *dst, struct page *src,
 		if (!likely(pte_same(*vmf->pte, vmf->orig_pte))) {
 			/*
 			 * Other thread has already handled the fault
-			 * and we don't need to do anything. If it's
-			 * not the case, the fault will be triggered
-			 * again on the same address.
+			 * and update local tlb only
 			 */
+			update_mmu_cache(vma, addr, vmf->pte);
 			ret = false;
 			goto pte_unlock;
 		}
 
 		entry = pte_mkyoung(vmf->orig_pte);
-		if (ptep_set_access_flags(vma, addr, vmf->pte, entry, 0))
-			update_mmu_cache(vma, addr, vmf->pte);
+		ptep_set_access_flags(vma, addr, vmf->pte, entry, 0);
+		update_mmu_cache(vma, addr, vmf->pte);
 	}
 
 	/*
@@ -2463,7 +2462,8 @@ static inline bool cow_user_page(struct page *dst, struct page *src,
 		vmf->pte = pte_offset_map_lock(mm, vmf->pmd, addr, &vmf->ptl);
 		locked = true;
 		if (!likely(pte_same(*vmf->pte, vmf->orig_pte))) {
-			/* The PTE changed under us. Retry page fault. */
+			/* The PTE changed under us, update local tlb */
+			pdate_mmu_cache(vma, addr, vmf->pte);
 			ret = false;
 			goto pte_unlock;
 		}
@@ -2618,8 +2618,8 @@ static inline void wp_page_reuse(struct vm_fault *vmf)
 	flush_cache_page(vma, vmf->address, pte_pfn(vmf->orig_pte));
 	entry = pte_mkyoung(vmf->orig_pte);
 	entry = maybe_mkwrite(pte_mkdirty(entry), vma);
-	if (ptep_set_access_flags(vma, vmf->address, vmf->pte, entry, 1))
-		update_mmu_cache(vma, vmf->address, vmf->pte);
+	ptep_set_access_flags(vma, vmf->address, vmf->pte, entry, 1);
+	update_mmu_cache(vma, vmf->address, vmf->pte);
 	pte_unmap_unlock(vmf->pte, vmf->ptl);
 }
 
@@ -2752,6 +2752,7 @@ static vm_fault_t wp_page_copy(struct vm_fault *vmf)
 		new_page = old_page;
 		page_copied = 1;
 	} else {
+		update_mmu_cache(vma, vmf->address, vmf->pte);
 		mem_cgroup_cancel_charge(new_page, memcg, false);
 	}
 
@@ -2812,6 +2813,7 @@ vm_fault_t finish_mkwrite_fault(struct vm_fault *vmf)
 	 * pte_offset_map_lock.
 	 */
 	if (!pte_same(*vmf->pte, vmf->orig_pte)) {
+		update_mmu_cache(vmf->vma, vmf->address, vmf->pte);
 		pte_unmap_unlock(vmf->pte, vmf->ptl);
 		return VM_FAULT_NOPAGE;
 	}
@@ -2936,6 +2938,7 @@ static vm_fault_t do_wp_page(struct vm_fault *vmf)
 			vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd,
 					vmf->address, &vmf->ptl);
 			if (!pte_same(*vmf->pte, vmf->orig_pte)) {
+				update_mmu_cache(vma, vmf->address, vmf->pte);
 				unlock_page(vmf->page);
 				pte_unmap_unlock(vmf->pte, vmf->ptl);
 				put_page(vmf->page);
@@ -3341,8 +3344,10 @@ static vm_fault_t do_anonymous_page(struct vm_fault *vmf)
 						vma->vm_page_prot));
 		vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd,
 				vmf->address, &vmf->ptl);
-		if (!pte_none(*vmf->pte))
+		if (!pte_none(*vmf->pte)) {
+			update_mmu_cache(vma, vmf->address, vmf->pte);
 			goto unlock;
+		}
 		ret = check_stable_address_space(vma->vm_mm);
 		if (ret)
 			goto unlock;
@@ -3378,8 +3383,10 @@ static vm_fault_t do_anonymous_page(struct vm_fault *vmf)
 
 	vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd, vmf->address,
 			&vmf->ptl);
-	if (!pte_none(*vmf->pte))
+	if (!pte_none(*vmf->pte)) {
+		update_mmu_cache(vma, vmf->address, vmf->pte);
 		goto release;
+	}
 
 	ret = check_stable_address_space(vma->vm_mm);
 	if (ret)
@@ -3646,8 +3653,10 @@ vm_fault_t alloc_set_pte(struct vm_fault *vmf, struct mem_cgroup *memcg,
 	}
 
 	/* Re-check under ptl */
-	if (unlikely(!pte_none(*vmf->pte)))
+	if (unlikely(!pte_none(*vmf->pte))) {
+		update_mmu_cache(vma, vmf->address, vmf->pte);
 		return VM_FAULT_NOPAGE;
+	}
 
 	flush_icache_page(vma, page);
 	entry = mk_pte(page, vma->vm_page_prot);
@@ -4224,18 +4233,18 @@ static vm_fault_t handle_pte_fault(struct vm_fault *vmf)
 	vmf->ptl = pte_lockptr(vmf->vma->vm_mm, vmf->pmd);
 	spin_lock(vmf->ptl);
 	entry = vmf->orig_pte;
-	if (unlikely(!pte_same(*vmf->pte, entry)))
+	if (unlikely(!pte_same(*vmf->pte, entry))) {
+		update_mmu_cache(vmf->vma, vmf->address, vmf->pte);
 		goto unlock;
+	}
 	if (vmf->flags & FAULT_FLAG_WRITE) {
 		if (!pte_write(entry))
 			return do_wp_page(vmf);
 		entry = pte_mkdirty(entry);
 	}
 	entry = pte_mkyoung(entry);
-	if (ptep_set_access_flags(vmf->vma, vmf->address, vmf->pte, entry,
+	if (!ptep_set_access_flags(vmf->vma, vmf->address, vmf->pte, entry,
 				vmf->flags & FAULT_FLAG_WRITE)) {
-		update_mmu_cache(vmf->vma, vmf->address, vmf->pte);
-	} else {
 		/*
 		 * This is needed only for protection faults but the arch code
 		 * is not yet telling us if this is a protection fault or not.
@@ -4245,6 +4254,7 @@ static vm_fault_t handle_pte_fault(struct vm_fault *vmf)
 		if (vmf->flags & FAULT_FLAG_WRITE)
 			flush_tlb_fix_spurious_fault(vmf->vma, vmf->address);
 	}
+	update_mmu_cache(vmf->vma, vmf->address, vmf->pte);
 unlock:
 	pte_unmap_unlock(vmf->pte, vmf->ptl);
 	return 0;
-- 
1.8.3.1