From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.7 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id EF975C432C3 for ; Wed, 13 Nov 2019 21:02:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A4823206ED for ; Wed, 13 Nov 2019 21:02:33 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727200AbfKMVCb (ORCPT ); Wed, 13 Nov 2019 16:02:31 -0500 Received: from Galois.linutronix.de ([193.142.43.55]:38943 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727068AbfKMVCY (ORCPT ); Wed, 13 Nov 2019 16:02:24 -0500 Received: from localhost ([127.0.0.1] helo=nanos.tec.linutronix.de) by Galois.linutronix.de with esmtp (Exim 4.80) (envelope-from ) id 1iUzmQ-00068D-Nt; Wed, 13 Nov 2019 22:02:22 +0100 Message-Id: <20191113210105.078437077@linutronix.de> User-Agent: quilt/0.65 Date: Wed, 13 Nov 2019 21:42:54 +0100 From: Thomas Gleixner To: LKML Cc: x86@kernel.org, Andy Lutomirski , Linus Torvalds , Stephen Hemminger , Willy Tarreau , Juergen Gross , Sean Christopherson , "H. Peter Anvin" Subject: [patch V3 14/20] x86/ioperm: Share I/O bitmap if identical References: <20191113204240.767922595@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Thomas Gleixner The I/O bitmap is duplicated on fork. That's wasting memory and slows down fork. There is no point to do so. As long as the bitmap is not modified it can be shared between threads and processes. Add a refcount and just share it on fork. If a task modifies the bitmap then it has to do the duplication if and only if it is shared. Signed-off-by: Thomas Gleixner Acked-by: Andy Lutomirski --- V3: Reset the ref count after duplicating io_bitmap. (Peter, Andy) V2: New patch --- arch/x86/include/asm/io_bitmap.h | 5 ++++ arch/x86/kernel/ioport.c | 48 +++++++++++++++++++++++++++++++-------- arch/x86/kernel/process.c | 39 ++++--------------------------- 3 files changed, 50 insertions(+), 42 deletions(-) --- a/arch/x86/include/asm/io_bitmap.h +++ b/arch/x86/include/asm/io_bitmap.h @@ -2,15 +2,20 @@ #ifndef _ASM_X86_IOBITMAP_H #define _ASM_X86_IOBITMAP_H +#include #include struct io_bitmap { u64 sequence; + refcount_t refcnt; /* The maximum number of bytes to copy so all zero bits are covered */ unsigned int max; unsigned long bitmap[IO_BITMAP_LONGS]; }; +struct task_struct; + +void io_bitmap_share(struct task_struct *tsk); void io_bitmap_exit(void); void tss_update_io_bitmap(void); --- a/arch/x86/kernel/ioport.c +++ b/arch/x86/kernel/ioport.c @@ -16,6 +16,17 @@ static atomic64_t io_bitmap_sequence; +void io_bitmap_share(struct task_struct *tsk) + { + /* + * Take a refcount on current's bitmap. It can be used by + * both tasks as long as none of them changes the bitmap. + */ + refcount_inc(¤t->thread.io_bitmap->refcnt); + tsk->thread.io_bitmap = current->thread.io_bitmap; + set_tsk_thread_flag(tsk, TIF_IO_BITMAP); +} + void io_bitmap_exit(void) { struct io_bitmap *iobm = current->thread.io_bitmap; @@ -25,7 +36,8 @@ void io_bitmap_exit(void) preempt_disable(); tss_update_io_bitmap(); preempt_enable(); - kfree(iobm); + if (iobm && refcount_dec_and_test(&iobm->refcnt)) + kfree(iobm); } /* @@ -58,9 +70,32 @@ long ksys_ioperm(unsigned long from, uns return -ENOMEM; memset(iobm->bitmap, 0xff, sizeof(iobm->bitmap)); + refcount_set(&iobm->refcnt, 1); + } + + /* + * If the bitmap is not shared, then nothing can take a refcount as + * current can obviously not fork at the same time. If it's shared + * duplicate it and drop the refcount on the original one. + */ + if (refcount_read(&iobm->refcnt) > 1) { + iobm = kmemdup(iobm, sizeof(*iobm), GFP_KERNEL); + if (!iobm) + return -ENOMEM; + refcount_set(&iobm->refcnt, 1); + io_bitmap_exit(); } /* + * Store the bitmap pointer (might be the same if the task already + * head one). Must be done here so freeing the bitmap when all + * permissions are dropped has the pointer set up. + */ + t->io_bitmap = iobm; + /* Mark it active for context switching and exit to user mode */ + set_thread_flag(TIF_IO_BITMAP); + + /* * Update the tasks bitmap. The update of the TSS bitmap happens on * exit to user mode. So this needs no protection. */ @@ -86,16 +121,11 @@ long ksys_ioperm(unsigned long from, uns iobm->max = (max_long + 1) * sizeof(unsigned long); - /* Update the sequence number to force an update in switch_to() */ - iobm->sequence = atomic64_add_return(1, &io_bitmap_sequence); - /* - * Store the bitmap pointer (might be the same if the task already - * head one). Set the TIF flag, just in case this is the first - * invocation. + * Update the sequence number to force a TSS update on return to + * user mode. */ - t->io_bitmap = iobm; - set_thread_flag(TIF_IO_BITMAP); + iobm->sequence = atomic64_add_return(1, &io_bitmap_sequence); return 0; } --- a/arch/x86/kernel/process.c +++ b/arch/x86/kernel/process.c @@ -122,37 +122,13 @@ static int set_new_tls(struct task_struc return do_set_thread_area_64(p, ARCH_SET_FS, tls); } -static inline int copy_io_bitmap(struct task_struct *tsk) -{ - struct io_bitmap *iobm = current->thread.io_bitmap; - - if (likely(!test_tsk_thread_flag(current, TIF_IO_BITMAP))) - return 0; - - tsk->thread.io_bitmap = kmemdup(iobm, sizeof(*iobm), GFP_KERNEL); - - if (!tsk->thread.io_bitmap) - return -ENOMEM; - - set_tsk_thread_flag(tsk, TIF_IO_BITMAP); - return 0; -} - -static inline void free_io_bitmap(struct task_struct *tsk) -{ - if (tsk->thread.io_bitmap) { - kfree(tsk->thread.io_bitmap); - tsk->thread.io_bitmap = NULL; - } -} - int copy_thread_tls(unsigned long clone_flags, unsigned long sp, unsigned long arg, struct task_struct *p, unsigned long tls) { struct inactive_task_frame *frame; struct fork_frame *fork_frame; struct pt_regs *childregs; - int ret; + int ret = 0; childregs = task_pt_regs(p); fork_frame = container_of(childregs, struct fork_frame, regs); @@ -193,16 +169,13 @@ int copy_thread_tls(unsigned long clone_ task_user_gs(p) = get_user_gs(current_pt_regs()); #endif - ret = copy_io_bitmap(p); - if (ret) - return ret; - /* Set a new TLS for the child thread? */ - if (clone_flags & CLONE_SETTLS) { + if (clone_flags & CLONE_SETTLS) ret = set_new_tls(p, tls); - if (ret) - free_io_bitmap(p); - } + + if (!ret && unlikely(test_tsk_thread_flag(current, TIF_IO_BITMAP))) + io_bitmap_share(p); + return ret; }