linux-kernel - [PATCH v2 1/4] mm: change page type prior to adding page table entry

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Message-Id: <20211204182314.1470076-2-pasha.tatashin@soleen.com>
Date:   Sat,  4 Dec 2021 18:23:11 +0000
From:   Pasha Tatashin <pasha.tatashin@...een.com>
To:     pasha.tatashin@...een.com, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linux-doc@...r.kernel.org,
        akpm@...ux-foundation.org, rientjes@...gle.com, pjt@...gle.com,
        weixugc@...gle.com, gthelen@...gle.com, mingo@...hat.com,
        corbet@....net, will@...nel.org, rppt@...nel.org,
        keescook@...omium.org, tglx@...utronix.de, peterz@...radead.org,
        masahiroy@...nel.org, samitolvanen@...gle.com,
        dave.hansen@...ux.intel.com, x86@...nel.org, frederic@...nel.org,
        hpa@...or.com, aneesh.kumar@...ux.ibm.com, jirislaby@...nel.org,
        songmuchun@...edance.com, qydwhotmail@...il.com
Subject: [PATCH v2 1/4] mm: change page type prior to adding page table entry

In do_swap_page() we first insert the entry into user page table, and
later change the struct page to indicate that this is anonymous page.

In all other places we first configure the page metadata and then insert
entries into the page table.

While odd, the behaviour is benign. Page table check, however, will use
the information from struct page to verify the type of entry is
inserted.

Change the order in do_swap_page() to first update struct page, and later
insert pte entry into the page table.

Signed-off-by: Pasha Tatashin <pasha.tatashin@...een.com>
---
 mm/memory.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index ced3274c3deb..9eef54950910 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3635,9 +3635,6 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
 		pte = pte_mkuffd_wp(pte);
 		pte = pte_wrprotect(pte);
 	}
-	set_pte_at(vma->vm_mm, vmf->address, vmf->pte, pte);
-	arch_do_swap_page(vma->vm_mm, vma, vmf->address, pte, vmf->orig_pte);
-	vmf->orig_pte = pte;
 
 	/* ksm created a completely new copy */
 	if (unlikely(page != swapcache && swapcache)) {
@@ -3647,6 +3644,10 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
 		do_page_add_anon_rmap(page, vma, vmf->address, exclusive);
 	}
 
+	set_pte_at(vma->vm_mm, vmf->address, vmf->pte, pte);
+	arch_do_swap_page(vma->vm_mm, vma, vmf->address, pte, vmf->orig_pte);
+	vmf->orig_pte = pte;
+
 	swap_free(entry);
 	if (mem_cgroup_swap_full(page) ||
 	    (vma->vm_flags & VM_LOCKED) || PageMlocked(page))
-- 
2.34.1.400.ga245620fadb-goog