linux-kernel - [PATCH v1 09/14] mm/mshare: Do not free PTEs for mshare'd PTEs

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Date:   Mon, 11 Apr 2022 10:05:53 -0600
From:   Khalid Aziz <khalid.aziz@...cle.com>
To:     akpm@...ux-foundation.org, willy@...radead.org
Cc:     Khalid Aziz <khalid.aziz@...cle.com>, aneesh.kumar@...ux.ibm.com,
        arnd@...db.de, 21cnbao@...il.com, corbet@....net,
        dave.hansen@...ux.intel.com, david@...hat.com,
        ebiederm@...ssion.com, hagen@...u.net, jack@...e.cz,
        keescook@...omium.org, kirill@...temov.name, kucharsk@...il.com,
        linkinjeon@...nel.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        longpeng2@...wei.com, luto@...nel.org, markhemm@...glemail.com,
        pcc@...gle.com, rppt@...nel.org, sieberf@...zon.com,
        sjpark@...zon.de, surenb@...gle.com, tst@...oebel-theuer.de,
        yzaikin@...gle.com
Subject: [PATCH v1 09/14] mm/mshare: Do not free PTEs for mshare'd PTEs

mshare'd PTEs should not be removed when a task exits. These PTEs
are removed when the last task sharing the PTEs exits. Add a check
for shared PTEs and skip them.

Signed-off-by: Khalid Aziz <khalid.aziz@...cle.com>
---
 mm/memory.c | 22 +++++++++++++++++++---
 1 file changed, 19 insertions(+), 3 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index c77c0d643ea8..e7c5bc6f8836 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -419,16 +419,25 @@ void free_pgtables(struct mmu_gather *tlb, struct vm_area_struct *vma,
 		} else {
 			/*
 			 * Optimization: gather nearby vmas into one call down
+			 * as long as they all belong to the same mm (that
+			 * may not be the case if a vma is part of mshare'd
+			 * range
 			 */
 			while (next && next->vm_start <= vma->vm_end + PMD_SIZE
-			       && !is_vm_hugetlb_page(next)) {
+			       && !is_vm_hugetlb_page(next)
+			       && vma->vm_mm == tlb->mm) {
 				vma = next;
 				next = vma->vm_next;
 				unlink_anon_vmas(vma);
 				unlink_file_vma(vma);
 			}
-			free_pgd_range(tlb, addr, vma->vm_end,
-				floor, next ? next->vm_start : ceiling);
+			/*
+			 * Free pgd only if pgd is not allocated for an
+			 * mshare'd range
+			 */
+			if (vma->vm_mm == tlb->mm)
+				free_pgd_range(tlb, addr, vma->vm_end,
+					floor, next ? next->vm_start : ceiling);
 		}
 		vma = next;
 	}
@@ -1551,6 +1560,13 @@ void unmap_page_range(struct mmu_gather *tlb,
 	pgd_t *pgd;
 	unsigned long next;
 
+	/*
+	 * If this is an mshare'd page, do not unmap it since it might
+	 * still be in use.
+	 */
+	if (vma->vm_mm != tlb->mm)
+		return;
+
 	BUG_ON(addr >= end);
 	tlb_start_vma(tlb, vma);
 	pgd = pgd_offset(vma->vm_mm, addr);
-- 
2.32.0