linux-kernel - [PATCH 20/29] mm: enable speculative fault handling in do_numa

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Date:   Fri, 30 Apr 2021 12:52:21 -0700
From:   Michel Lespinasse <michel@...pinasse.org>
To:     Linux-MM <linux-mm@...ck.org>,
        Linux-Kernel <linux-kernel@...r.kernel.org>
Cc:     Laurent Dufour <ldufour@...ux.ibm.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Michal Hocko <mhocko@...e.com>,
        Matthew Wilcox <willy@...radead.org>,
        Rik van Riel <riel@...riel.com>,
        Paul McKenney <paulmck@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Joel Fernandes <joelaf@...gle.com>,
        Andy Lutomirski <luto@...nel.org>,
        Michel Lespinasse <michel@...pinasse.org>
Subject: [PATCH 20/29] mm: enable speculative fault handling in do_numa_page()

Change handle_pte_fault() to allow speculative fault execution to proceed
through do_numa_page().

do_swap_page() does not implement speculative execution yet, so it
needs to abort with VM_FAULT_RETRY in that case.

Signed-off-by: Michel Lespinasse <michel@...pinasse.org>
---
 mm/memory.c | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index a2230269e034..286776b7795b 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3363,6 +3363,11 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
 	vm_fault_t ret = 0;
 	void *shadow = NULL;
 
+	if (vmf->flags & FAULT_FLAG_SPECULATIVE) {
+		pte_unmap(vmf->pte);
+		return VM_FAULT_RETRY;
+	}
+
 	if (!pte_unmap_same(vma->vm_mm, vmf->pmd, vmf->pte, vmf->orig_pte))
 		goto out;
 
@@ -4359,17 +4364,17 @@ static vm_fault_t handle_pte_fault(struct vm_fault *vmf)
 			return do_fault(vmf);
 	}
 
-	if (vmf->flags & FAULT_FLAG_SPECULATIVE) {
-		pte_unmap(vmf->pte);
-		return VM_FAULT_RETRY;
-	}
-
 	if (!pte_present(vmf->orig_pte))
 		return do_swap_page(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);
+		return VM_FAULT_RETRY;
+	}
+
 	vmf->ptl = pte_lockptr(vmf->vma->vm_mm, vmf->pmd);
 	spin_lock(vmf->ptl);
 	entry = vmf->orig_pte;
-- 
2.20.1