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Subject[PATCH 2/2] s390/mm: allow gmap code to retry on faulting in guest memory
Date
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@linux.vnet.ibm.com>
---
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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