linux-kernel - [PATCH v2 9/9] mm/mshare: Enable mshare region mapping across processes

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Date:   Wed, 29 Jun 2022 16:54:00 -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 v2 9/9] mm/mshare: Enable mshare region mapping across processes

This patch enables propcesses that did not create the mshare region
to map the region using mmap().

Signed-off-by: Khalid Aziz <khalid.aziz@...cle.com>
---
 mm/mshare.c | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/mm/mshare.c b/mm/mshare.c
index 2ec0e56ffd69..455b10ca0cdf 100644
--- a/mm/mshare.c
+++ b/mm/mshare.c
@@ -144,7 +144,21 @@ msharefs_mmap(struct file *file, struct vm_area_struct *vma)
 	 * page table sharing
 	 */
 	if (new_mm->mmap_base != 0) {
-		return -EINVAL;
+		/*
+		 * Any mappings of mshare region must use exact same
+		 * virtual addresses
+		 */
+		if ((vma->vm_start != new_mm->mmap_base) ||
+			(new_mm->task_size != (vma->vm_end - vma->vm_start)))
+			return -EINVAL;
+
+		vma->vm_private_data = info;
+		/*
+		 * mshare pages are shared pages that also share page table
+		 */
+		vma->vm_flags |= (VM_SHARED_PT|VM_SHARED);
+		vma->vm_ops = &msharefs_vm_ops;
+		refcount_inc(&info->refcnt);
 	} else {
 		struct mm_struct *old_mm;
 		struct vm_area_struct *new_vma;
-- 
2.32.0