[RFC PATCH 15/37] mm: implement speculative handling in do_anonymous_page()

[Michel Lespinasse]

Change do_anonymous_page() to handle the speculative case.
This involves aborting speculative faults if they have to allocate a new
anon_vma, and using pte_map_lock() instead of pte_offset_map_lock()
to complete the page fault.

Signed-off-by: Michel Lespinasse <mic...@lespinasse.org>
---
 mm/memory.c | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index 3e192d5f89a6..fd84576f9c01 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3598,8 +3598,12 @@ static vm_fault_t do_anonymous_page(struct vm_fault *vmf)
                                                vma->vm_page_prot));
        } else {
                /* Allocate our own private page. */
-               if (unlikely(anon_vma_prepare(vma)))
-                       goto oom;
+               if (unlikely(!vma->anon_vma)) {
+                       if (vmf->flags & FAULT_FLAG_SPECULATIVE)
+                               return VM_FAULT_RETRY;
+                       if (__anon_vma_prepare(vma))
+                               goto oom;
+               }
                page = alloc_zeroed_user_highpage_movable(vma, vmf->address);
                if (!page)
                        goto oom;
@@ -3620,8 +3624,10 @@ static vm_fault_t do_anonymous_page(struct vm_fault *vmf)
                        entry = pte_mkwrite(pte_mkdirty(entry));
        }
 
-       vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd, vmf->address,
-                       &vmf->ptl);
+       if (!pte_map_lock(vmf)) {
+               ret = VM_FAULT_RETRY;
+               goto release;
+       }
        if (!pte_none(*vmf->pte)) {
                update_mmu_tlb(vma, vmf->address, vmf->pte);
                goto unlock;
@@ -3636,6 +3642,8 @@ static vm_fault_t do_anonymous_page(struct vm_fault *vmf)
                pte_unmap_unlock(vmf->pte, vmf->ptl);
                if (page)
                        put_page(page);
+               if (vmf->flags & FAULT_FLAG_SPECULATIVE)
+                       return VM_FAULT_RETRY;
                return handle_userfault(vmf, VM_UFFD_MISSING);
        }
 
@@ -3653,6 +3661,7 @@ static vm_fault_t do_anonymous_page(struct vm_fault *vmf)
        return 0;
 unlock:
        pte_unmap_unlock(vmf->pte, vmf->ptl);
+release:
        if (page)
                put_page(page);
        return ret;
-- 
2.20.1