[PATCH 2/2] s390/mm: enable fixup_user_fault retrying

Dominik Dingel
2016-01-04T11:20:45Z

By passing a non-null flag we allow fixup_user_fault to retry, which
enables userfaultfd. As during these retries we might drop the mmap_sem we
need to check if that happened and redo the complete chain of actions.

Signed-off-by: Dominik Dingel <dingel@linux.vnet.ibm.com>
---
arch/s390/mm/pgtable.c | 29 ++++++++++++++++++++++++++---
1 file changed, 26 insertions(+), 3 deletions(-)

diff --git a/arch/s390/mm/pgtable.c b/arch/s390/mm/pgtable.c
index b15759c..3c5456d 100644
--- a/arch/s390/mm/pgtable.c
+++ b/arch/s390/mm/pgtable.c
@@ -578,17 +578,29 @@ int gmap_fault(struct gmap *gmap, unsigned long gaddr,
{
unsigned long vmaddr;
int rc;
+ bool unlocked;

down_read(&gmap->mm->mmap_sem);
+
+retry:
+ unlocked = false;
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, NULL)) {
+ if (fixup_user_fault(current, gmap->mm, vmaddr, fault_flags,
+ &unlocked)) {
rc = -EFAULT;
goto out_up;
}
+ /*
+ * In the case that fixup_user_fault unlocked the mmap_sem during
+ * faultin redo __gmap_translate to not race with a map/unmap_segment.
+ */
+ if (unlocked)
+ goto retry;
+
rc = __gmap_link(gmap, gaddr, vmaddr);
out_up:
up_read(&gmap->mm->mmap_sem);
@@ -717,12 +729,14 @@ int gmap_ipte_notify(struct gmap *gmap, unsigned long gaddr, unsigned long len)
spinlock_t *ptl;
pte_t *ptep, entry;
pgste_t pgste;
+ bool unlocked;
int rc = 0;

if ((gaddr & ~PAGE_MASK) || (len & ~PAGE_MASK))
return -EINVAL;
down_read(&gmap->mm->mmap_sem);
while (len) {
+ unlocked = false;
/* Convert gmap address and connect the page tables */
addr = __gmap_translate(gmap, gaddr);
if (IS_ERR_VALUE(addr)) {
@@ -731,10 +745,13 @@ int gmap_ipte_notify(struct gmap *gmap, unsigned long gaddr, unsigned long len)
}
/* Get the page mapped */
if (fixup_user_fault(current, gmap->mm, addr, FAULT_FLAG_WRITE,
- NULL)) {
+ &unlocked)) {
rc = -EFAULT;
break;
}
+ /* While trying to map mmap_sem got unlocked. Let us retry */
+ if (unlocked)
+ continue;
rc = __gmap_link(gmap, gaddr, addr);
if (rc)
break;
@@ -795,9 +812,11 @@ int set_guest_storage_key(struct mm_struct *mm, unsigned long addr,
spinlock_t *ptl;
pgste_t old, new;
pte_t *ptep;
+ bool unlocked;

down_read(&mm->mmap_sem);
retry:
+ unlocked = false;
ptep = get_locked_pte(mm, addr, &ptl);
if (unlikely(!ptep)) {
up_read(&mm->mmap_sem);
@@ -806,8 +825,12 @@ retry:
if (!(pte_val(*ptep) & _PAGE_INVALID) &&
(pte_val(*ptep) & _PAGE_PROTECT)) {
pte_unmap_unlock(ptep, ptl);
+ /*
+ * We do not really care about unlocked. We will retry either
+ * way. But this allows fixup_user_fault to enable userfaultfd.
+ */
if (fixup_user_fault(current, mm, addr, FAULT_FLAG_WRITE,
- NULL)) {
+ &unlocked)) {
up_read(&mm->mmap_sem);
return -EFAULT;
}
--
2.3.0