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Message-Id: <20220128131006.67712-28-michel@lespinasse.org>
Date: Fri, 28 Jan 2022 05:09:58 -0800
From: Michel Lespinasse <michel@...pinasse.org>
To: Linux-MM <linux-mm@...ck.org>, linux-kernel@...r.kernel.org,
Andrew Morton <akpm@...ux-foundation.org>
Cc: kernel-team@...com, Laurent Dufour <ldufour@...ux.ibm.com>,
Jerome Glisse <jglisse@...gle.com>,
Peter Zijlstra <peterz@...radead.org>,
Michal Hocko <mhocko@...e.com>,
Vlastimil Babka <vbabka@...e.cz>,
Davidlohr Bueso <dave@...olabs.net>,
Matthew Wilcox <willy@...radead.org>,
Liam Howlett <liam.howlett@...cle.com>,
Rik van Riel <riel@...riel.com>,
Paul McKenney <paulmck@...nel.org>,
Song Liu <songliubraving@...com>,
Suren Baghdasaryan <surenb@...gle.com>,
Minchan Kim <minchan@...gle.com>,
Joel Fernandes <joelaf@...gle.com>,
David Rientjes <rientjes@...gle.com>,
Axel Rasmussen <axelrasmussen@...gle.com>,
Andy Lutomirski <luto@...nel.org>,
Michel Lespinasse <michel@...pinasse.org>
Subject: [PATCH v2 27/35] mm: implement and enable speculative fault handling in handle_pte_fault()
In handle_pte_fault(), allow speculative execution to proceed.
Use pte_spinlock() to validate the mmap sequence count when locking
the page table.
If speculative execution proceeds through do_wp_page(), ensure that we
end up in the wp_page_reuse() or wp_page_copy() paths, rather than
wp_pfn_shared() or wp_page_shared() (both unreachable as we only
handle anon vmas so far) or handle_userfault() (needs an explicit
abort to handle non-speculatively).
Signed-off-by: Michel Lespinasse <michel@...pinasse.org>
---
mm/memory.c | 12 ++++++------
1 file changed, 6 insertions(+), 6 deletions(-)
diff --git a/mm/memory.c b/mm/memory.c
index fd8984d89109..7f8dbd729dce 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3293,6 +3293,7 @@ static vm_fault_t wp_pfn_shared(struct vm_fault *vmf)
{
struct vm_area_struct *vma = vmf->vma;
+ VM_BUG_ON(vmf->flags & FAULT_FLAG_SPECULATIVE);
if (vma->vm_ops && vma->vm_ops->pfn_mkwrite) {
vm_fault_t ret;
@@ -3313,6 +3314,8 @@ static vm_fault_t wp_page_shared(struct vm_fault *vmf)
struct vm_area_struct *vma = vmf->vma;
vm_fault_t ret = VM_FAULT_WRITE;
+ VM_BUG_ON(vmf->flags & FAULT_FLAG_SPECULATIVE);
+
get_page(vmf->page);
if (vma->vm_ops && vma->vm_ops->page_mkwrite) {
@@ -3366,6 +3369,8 @@ static vm_fault_t do_wp_page(struct vm_fault *vmf)
if (userfaultfd_pte_wp(vma, *vmf->pte)) {
pte_unmap_unlock(vmf->pte, vmf->ptl);
+ if (vmf->flags & FAULT_FLAG_SPECULATIVE)
+ return VM_FAULT_RETRY;
return handle_userfault(vmf, VM_UFFD_WP);
}
@@ -4646,13 +4651,8 @@ static vm_fault_t handle_pte_fault(struct vm_fault *vmf)
if (pte_protnone(vmf->orig_pte) && vma_is_accessible(vmf->vma))
return do_numa_page(vmf);
- if (vmf->flags & FAULT_FLAG_SPECULATIVE) {
- pte_unmap(vmf->pte);
+ if (!pte_spinlock(vmf))
return VM_FAULT_RETRY;
- }
-
- vmf->ptl = pte_lockptr(vmf->vma->vm_mm, vmf->pmd);
- spin_lock(vmf->ptl);
entry = vmf->orig_pte;
if (unlikely(!pte_same(*vmf->pte, entry))) {
update_mmu_tlb(vmf->vma, vmf->address, vmf->pte);
--
2.20.1
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