linux-kernel - [RFC PATCH 2/6] mm: clone3: Add CLONE_COW

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Date:   Fri, 20 May 2022 02:31:23 +0800
From:   Chih-En Lin <shiyn.lin@...il.com>
To:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org
Cc:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Christian Brauner <brauner@...nel.org>,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        William Kucharski <william.kucharski@...cle.com>,
        John Hubbard <jhubbard@...dia.com>,
        Yunsheng Lin <linyunsheng@...wei.com>,
        Arnd Bergmann <arnd@...db.de>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Chih-En Lin <shiyn.lin@...il.com>,
        Colin Cross <ccross@...gle.com>,
        Feng Tang <feng.tang@...el.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Mike Rapoport <rppt@...nel.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Anshuman Khandual <anshuman.khandual@....com>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
        Daniel Axtens <dja@...ens.net>,
        Jonathan Marek <jonathan@...ek.ca>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Pasha Tatashin <pasha.tatashin@...een.com>,
        Peter Xu <peterx@...hat.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andy Lutomirski <luto@...nel.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Fenghua Yu <fenghua.yu@...el.com>,
        David Hildenbrand <david@...hat.com>,
        linux-kernel@...r.kernel.org, Kaiyang Zhao <zhao776@...due.edu>,
        Huichun Feng <foxhoundsk.tw@...il.com>,
        Jim Huang <jserv.tw@...il.com>
Subject: [RFC PATCH 2/6] mm: clone3: Add CLONE_COW_PGTABLE flag

Add CLONE_COW_PGTABLE flag to support clone3() system call to enable the
Copy-On-Write (COW) mechanism on the page table.

Signed-off-by: Chih-En Lin <shiyn.lin@...il.com>
---
 include/uapi/linux/sched.h | 1 +
 kernel/fork.c              | 6 +++++-
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/include/uapi/linux/sched.h b/include/uapi/linux/sched.h
index 3bac0a8ceab2..3b92ff589e0f 100644
--- a/include/uapi/linux/sched.h
+++ b/include/uapi/linux/sched.h
@@ -36,6 +36,7 @@
 /* Flags for the clone3() syscall. */
 #define CLONE_CLEAR_SIGHAND 0x100000000ULL /* Clear any signal handler and reset to SIG_DFL. */
 #define CLONE_INTO_CGROUP 0x200000000ULL /* Clone into a specific cgroup given the right permissions. */
+#define CLONE_COW_PGTABLE 0x400000000ULL /* Copy-On-Write for page table */
 
 /*
  * cloning flags intersect with CSIGNAL so can be used with unshare and clone3
diff --git a/kernel/fork.c b/kernel/fork.c
index 35a3beff140b..08cf95201333 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -2636,6 +2636,9 @@ pid_t kernel_clone(struct kernel_clone_args *args)
 			trace = 0;
 	}
 
+	if (clone_flags & CLONE_COW_PGTABLE)
+		set_bit(MMF_COW_PGTABLE, &current->mm->flags);
+
 	p = copy_process(NULL, trace, NUMA_NO_NODE, args);
 	add_latent_entropy();
 
@@ -2860,7 +2863,8 @@ static bool clone3_args_valid(struct kernel_clone_args *kargs)
 {
 	/* Verify that no unknown flags are passed along. */
 	if (kargs->flags &
-	    ~(CLONE_LEGACY_FLAGS | CLONE_CLEAR_SIGHAND | CLONE_INTO_CGROUP))
+	    ~(CLONE_LEGACY_FLAGS | CLONE_CLEAR_SIGHAND | CLONE_INTO_CGROUP |
+		    CLONE_COW_PGTABLE))
 		return false;
 
 	/*
-- 
2.36.1