[PATCH 06/14] mm/hmm: remove HMM_PFN_READ flag and ignore peculiar architecture

[jglisse@redhat.com]

From: JA(C)rA'me Glisse <jglisse@redhat.com>

Only peculiar architecture allow write without read thus assume that
any valid pfn do allow for read. Note we do not care for write only
because it does make sense with thing like atomic compare and exchange
or any other operations that allow you to get the memory value through
them.

Signed-off-by: JA(C)rA'me Glisse <jglisse@redhat.com>
Cc: Evgeny Baskakov <ebaskakov@nvidia.com>
Cc: Ralph Campbell <rcampbell@nvidia.com>
Cc: Mark Hairgrove <mhairgrove@nvidia.com>
Cc: John Hubbard <jhubbard@nvidia.com>
---
 include/linux/hmm.h | 14 ++++++--------
 mm/hmm.c            | 28 ++++++++++++++++++++++++----
 2 files changed, 30 insertions(+), 12 deletions(-)

diff --git a/include/linux/hmm.h b/include/linux/hmm.h
index b65e527dd120..4bdc58ffe9f3 100644
--- a/include/linux/hmm.h
+++ b/include/linux/hmm.h
@@ -84,7 +84,6 @@ struct hmm;
  *
  * Flags:
  * HMM_PFN_VALID: pfn is valid
- * HMM_PFN_READ:  CPU page table has read permission set
  * HMM_PFN_WRITE: CPU page table has write permission set
  * HMM_PFN_ERROR: corresponding CPU page table entry points to poisoned memory
  * HMM_PFN_EMPTY: corresponding CPU page table entry is pte_none()
@@ -97,13 +96,12 @@ struct hmm;
 typedef unsigned long hmm_pfn_t;
 
 #define HMM_PFN_VALID (1 << 0)
-#define HMM_PFN_READ (1 << 1)
-#define HMM_PFN_WRITE (1 << 2)
-#define HMM_PFN_ERROR (1 << 3)
-#define HMM_PFN_EMPTY (1 << 4)
-#define HMM_PFN_SPECIAL (1 << 5)
-#define HMM_PFN_DEVICE_UNADDRESSABLE (1 << 6)
-#define HMM_PFN_SHIFT 7
+#define HMM_PFN_WRITE (1 << 1)
+#define HMM_PFN_ERROR (1 << 2)
+#define HMM_PFN_EMPTY (1 << 3)
+#define HMM_PFN_SPECIAL (1 << 4)
+#define HMM_PFN_DEVICE_UNADDRESSABLE (1 << 5)
+#define HMM_PFN_SHIFT 6
 
 /*
  * hmm_pfn_t_to_page() - return struct page pointed to by a valid hmm_pfn_t
diff --git a/mm/hmm.c b/mm/hmm.c
index 49f0f6b337ed..fa3c605c4b96 100644
--- a/mm/hmm.c
+++ b/mm/hmm.c
@@ -374,11 +374,9 @@ static int hmm_vma_walk_pmd(pmd_t *pmdp,
 	hmm_pfn_t *pfns = range->pfns;
 	unsigned long addr = start, i;
 	bool write_fault;
-	hmm_pfn_t flag;
 	pte_t *ptep;
 
 	i = (addr - range->start) >> PAGE_SHIFT;
-	flag = vma->vm_flags & VM_READ ? HMM_PFN_READ : 0;
 	write_fault = hmm_vma_walk->fault & hmm_vma_walk->write;
 
 again:
@@ -390,6 +388,7 @@ static int hmm_vma_walk_pmd(pmd_t *pmdp,
 
 	if (pmd_devmap(*pmdp) || pmd_trans_huge(*pmdp)) {
 		unsigned long pfn;
+		hmm_pfn_t flag = 0;
 		pmd_t pmd;
 
 		/*
@@ -454,7 +453,6 @@ static int hmm_vma_walk_pmd(pmd_t *pmdp,
 				} else if (write_fault)
 					goto fault;
 				pfns[i] |= HMM_PFN_DEVICE_UNADDRESSABLE;
-				pfns[i] |= flag;
 			} else if (is_migration_entry(entry)) {
 				if (hmm_vma_walk->fault) {
 					pte_unmap(ptep);
@@ -474,7 +472,7 @@ static int hmm_vma_walk_pmd(pmd_t *pmdp,
 		if (write_fault && !pte_write(pte))
 			goto fault;
 
-		pfns[i] = hmm_pfn_t_from_pfn(pte_pfn(pte)) | flag;
+		pfns[i] = hmm_pfn_t_from_pfn(pte_pfn(pte));
 		pfns[i] |= pte_write(pte) ? HMM_PFN_WRITE : 0;
 		continue;
 
@@ -536,6 +534,17 @@ int hmm_vma_get_pfns(struct hmm_range *range)
 	list_add_rcu(&range->list, &hmm->ranges);
 	spin_unlock(&hmm->lock);
 
+	if (!(vma->vm_flags & VM_READ)) {
+		/*
+		 * If vma do not allow read assume it does not allow write as
+		 * only peculiar architecture allow write without read and this
+		 * is not a case we care about (some operation like atomic no
+		 * longer make sense).
+		 */
+		hmm_pfns_clear(range->pfns, range->start, range->end);
+		return 0;
+	}
+
 	hmm_vma_walk.fault = false;
 	hmm_vma_walk.range = range;
 	mm_walk.private = &hmm_vma_walk;
@@ -690,6 +699,17 @@ int hmm_vma_fault(struct hmm_range *range, bool write, bool block)
 	list_add_rcu(&range->list, &hmm->ranges);
 	spin_unlock(&hmm->lock);
 
+	if (!(vma->vm_flags & VM_READ)) {
+		/*
+		 * If vma do not allow read assume it does not allow write as
+		 * only peculiar architecture allow write without read and this
+		 * is not a case we care about (some operation like atomic no
+		 * longer make sense).
+		 */
+		hmm_pfns_clear(range->pfns, range->start, range->end);
+		return 0;
+	}
+
 	/* FIXME support hugetlb fs */
 	if (is_vm_hugetlb_page(vma) || (vma->vm_flags & VM_SPECIAL)) {
 		hmm_pfns_special(range->pfns, range->start, range->end);
-- 
2.14.3