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Howlett" , Alex Sierra , Xianting Tian , Colin Cross , Suren Baghdasaryan , Barry Song , Pasha Tatashin , Suleiman Souhlal , Brian Geffon , Yu Zhao , Tong Tiangen , Liu Shixin , Li kunyu , Anshuman Khandual , Vlastimil Babka , Hugh Dickins , Minchan Kim , Miaohe Lin , Gautam Menghani , Catalin Marinas , Mark Brown , Will Deacon , "Eric W . Biederman" , Thomas Gleixner , Sebastian Andrzej Siewior , Andy Lutomirski , Fenghua Yu , Barret Rhoden , Davidlohr Bueso , "Jason A . Donenfeld" , Dinglan Peng , Pedro Fonseca , Jim Huang , Huichun Feng , Chih-En Lin Subject: [PATCH v3 01/14] mm: Allow user to control COW PTE via prctl Date: Tue, 20 Dec 2022 15:27:30 +0800 Message-Id: <20221220072743.3039060-2-shiyn.lin@gmail.com> X-Mailer: git-send-email 2.37.3 In-Reply-To: <20221220072743.3039060-1-shiyn.lin@gmail.com> References: <20221220072743.3039060-1-shiyn.lin@gmail.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Add a new prctl, PR_SET_COW_PTE, to allow the user to enable COW PTE. Since it has a time gap between using the prctl to enable the COW PTE and doing the fork, we use two states (MMF_COW_PTE_READY and MMF_COW_PTE) to determine the task that wants to do COW PTE or already doing it. The MMF_COW_PTE_READY flag marks the task to do COW PTE in the next time of fork(). During fork(), if MMF_COW_PTE_READY set, fork() will unset the flag and set the MMF_COW_PTE flag. After that, fork() might shares PTEs instead of duplicates it. Signed-off-by: Chih-En Lin --- include/linux/sched/coredump.h | 12 +++++++++++- include/uapi/linux/prctl.h | 6 ++++++ kernel/sys.c | 11 +++++++++++ 3 files changed, 28 insertions(+), 1 deletion(-) diff --git a/include/linux/sched/coredump.h b/include/linux/sched/coredump.h index 8270ad7ae14c2..570d599ebc851 100644 --- a/include/linux/sched/coredump.h +++ b/include/linux/sched/coredump.h @@ -83,7 +83,17 @@ static inline int get_dumpable(struct mm_struct *mm) #define MMF_HAS_PINNED 27 /* FOLL_PIN has run, never cleared */ #define MMF_DISABLE_THP_MASK (1 << MMF_DISABLE_THP) +/* + * MMF_COW_PTE_READY: Marking the task to do COW PTE in the next time of + * fork(). During fork(), if MMF_COW_PTE_READY set, fork() will unset the + * flag and set the MMF_COW_PTE flag. After that, fork() might shares PTEs + * rather than duplicates it. + */ +#define MMF_COW_PTE_READY 29 /* Share PTE tables in next time of fork() */ +#define MMF_COW_PTE 30 /* PTE tables are shared between processes */ +#define MMF_COW_PTE_MASK (1 << MMF_COW_PTE) + #define MMF_INIT_MASK (MMF_DUMPABLE_MASK | MMF_DUMP_FILTER_MASK |\ - MMF_DISABLE_THP_MASK) + MMF_DISABLE_THP_MASK | MMF_COW_PTE_MASK) #endif /* _LINUX_SCHED_COREDUMP_H */ diff --git a/include/uapi/linux/prctl.h b/include/uapi/linux/prctl.h index a5e06dcbba136..664a3c0230192 100644 --- a/include/uapi/linux/prctl.h +++ b/include/uapi/linux/prctl.h @@ -284,4 +284,10 @@ struct prctl_mm_map { #define PR_SET_VMA 0x53564d41 # define PR_SET_VMA_ANON_NAME 0 +/* + * Set the prepare flag, MMF_COW_PTE_READY, to do the share (copy-on-write) + * page table in the next time of fork. + */ +#define PR_SET_COW_PTE 65 + #endif /* _LINUX_PRCTL_H */ diff --git a/kernel/sys.c b/kernel/sys.c index 5fd54bf0e8867..d1062ea33981e 100644 --- a/kernel/sys.c +++ b/kernel/sys.c @@ -2348,6 +2348,14 @@ static int prctl_set_vma(unsigned long opt, unsigned long start, } #endif /* CONFIG_ANON_VMA_NAME */ +static int prctl_set_cow_pte(struct mm_struct *mm) +{ + if (test_bit(MMF_COW_PTE, &mm->flags)) + return -EINVAL; + set_bit(MMF_COW_PTE_READY, &mm->flags); + return 0; +} + SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3, unsigned long, arg4, unsigned long, arg5) { @@ -2626,6 +2634,9 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3, case PR_SET_VMA: error = prctl_set_vma(arg2, arg3, arg4, arg5); break; + case PR_SET_COW_PTE: + error = prctl_set_cow_pte(me->mm); + break; default: error = -EINVAL; break; -- 2.37.3