[PATCH 2/2] s390/mm: allow gmap code to retry on faulting in guest memory

[Dominik Dingel <dingel@xxxxxxxxxxxxxxxxxx>]

The userfaultfd does need FAULT_FLAG_ALLOW_RETRY to not return
VM_FAULT_SIGBUS.  So we improve the gmap code to handle one
VM_FAULT_RETRY.

Signed-off-by: Dominik Dingel <dingel@xxxxxxxxxxxxxxxxxx>
---
 arch/s390/mm/pgtable.c | 28 ++++++++++++++++++++++++----
 1 file changed, 24 insertions(+), 4 deletions(-)

diff --git a/arch/s390/mm/pgtable.c b/arch/s390/mm/pgtable.c
index 54ef3bc..8a0025d 100644
--- a/arch/s390/mm/pgtable.c
+++ b/arch/s390/mm/pgtable.c
@@ -577,15 +577,22 @@ int gmap_fault(struct gmap *gmap, unsigned long gaddr,
 	       unsigned int fault_flags)
 {
 	unsigned long vmaddr;
-	int rc;
+	int rc, fault;
 
+	fault_flags |= FAULT_FLAG_ALLOW_RETRY;
+retry:
 	down_read(&gmap->mm->mmap_sem);
 	vmaddr = __gmap_translate(gmap, gaddr);
 	if (IS_ERR_VALUE(vmaddr)) {
 		rc = vmaddr;
 		goto out_up;
 	}
-	if (fixup_user_fault(current, gmap->mm, vmaddr, fault_flags)) {
+	fault = fixup_user_fault(current, gmap->mm, vmaddr, fault_flags);
+	if (fault & VM_FAULT_RETRY) {
+		fault_flags &= ~FAULT_FLAG_ALLOW_RETRY;
+		fault_flags |= FAULT_FLAG_TRIED;
+		goto retry;
+	} else if (fault) {
 		rc = -EFAULT;
 		goto out_up;
 	}
@@ -717,10 +724,13 @@ int gmap_ipte_notify(struct gmap *gmap, unsigned long gaddr, unsigned long len)
 	spinlock_t *ptl;
 	pte_t *ptep, entry;
 	pgste_t pgste;
+	int fault, fault_flags;
 	int rc = 0;
 
+	fault_flags = FAULT_FLAG_WRITE | FAULT_FLAG_ALLOW_RETRY;
 	if ((gaddr & ~PAGE_MASK) || (len & ~PAGE_MASK))
 		return -EINVAL;
+retry:
 	down_read(&gmap->mm->mmap_sem);
 	while (len) {
 		/* Convert gmap address and connect the page tables */
@@ -730,7 +740,12 @@ int gmap_ipte_notify(struct gmap *gmap, unsigned long gaddr, unsigned long len)
 			break;
 		}
 		/* Get the page mapped */
-		if (fixup_user_fault(current, gmap->mm, addr, FAULT_FLAG_WRITE)) {
+		fault = fixup_user_fault(current, gmap->mm, addr, fault_flags);
+		if (fault & VM_FAULT_RETRY) {
+			fault_flags &= ~FAULT_FLAG_ALLOW_RETRY;
+			fault_flags |= FAULT_FLAG_TRIED;
+			goto retry;
+		} else if (fault) {
 			rc = -EFAULT;
 			break;
 		}
@@ -794,7 +809,9 @@ int set_guest_storage_key(struct mm_struct *mm, unsigned long addr,
 	spinlock_t *ptl;
 	pgste_t old, new;
 	pte_t *ptep;
+	int fault, fault_flags;
 
+	fault_flags = FAULT_FLAG_WRITE | FAULT_FLAG_ALLOW_RETRY;
 	down_read(&mm->mmap_sem);
 retry:
 	ptep = get_locked_pte(mm, addr, &ptl);
@@ -805,10 +822,13 @@ retry:
 	if (!(pte_val(*ptep) & _PAGE_INVALID) &&
 	     (pte_val(*ptep) & _PAGE_PROTECT)) {
 		pte_unmap_unlock(ptep, ptl);
-		if (fixup_user_fault(current, mm, addr, FAULT_FLAG_WRITE)) {
+		fault = fixup_user_fault(current, mm, addr, fault_flags);
+		if (fault && !(fault & VM_FAULT_RETRY)) {
 			up_read(&mm->mmap_sem);
 			return -EFAULT;
 		}
+		fault_flags &= ~FAULT_FLAG_ALLOW_RETRY;
+		fault_flags |= FAULT_FLAG_TRIED;
 		goto retry;
 	}
 
-- 
2.3.9

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