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From: Andy Lutomirski <luto@kernel.org>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: LKML <linux-kernel@vger.kernel.org>, X86 ML <x86@kernel.org>,
	Linus Torvalds <torvalds@linuxfoundation.org>,
	Andy Lutomirski <luto@kernel.org>,
	Stephen Hemminger <stephen@networkplumber.org>,
	Willy Tarreau <w@1wt.eu>, Juergen Gross <jgross@suse.com>,
	Sean Christopherson <sean.j.christopherson@intel.com>,
	"H. Peter Anvin" <hpa@zytor.com>
Subject: Re: [patch V2 11/16] x86/ioperm: Share I/O bitmap if identical
Date: Tue, 12 Nov 2019 10:12:14 -0800	[thread overview]
Message-ID: <CALCETrVXV61hN__tf-TakJCLnM6rVZ-5x7U2eeojadovhk6AJg@mail.gmail.com> (raw)
In-Reply-To: <20191111223052.603030685@linutronix.de>

On Mon, Nov 11, 2019 at 2:35 PM Thomas Gleixner <tglx@linutronix.de> wrote:
>
> 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 <tglx@linutronix.de>
> ---
> V2: New patch
> ---
>  arch/x86/include/asm/iobitmap.h |    5 +++++
>  arch/x86/kernel/ioport.c        |   38 ++++++++++++++++++++++++++++++++------
>  arch/x86/kernel/process.c       |   39 ++++++---------------------------------
>  3 files changed, 43 insertions(+), 39 deletions(-)
>
> --- a/arch/x86/include/asm/iobitmap.h
> +++ b/arch/x86/include/asm/iobitmap.h
> @@ -2,10 +2,12 @@
>  #ifndef _ASM_X86_IOBITMAP_H
>  #define _ASM_X86_IOBITMAP_H
>
> +#include <linux/refcount.h>
>  #include <asm/processor.h>
>
>  struct io_bitmap {
>         u64                     sequence;
> +       refcount_t              refcnt;
>         unsigned int            io_bitmap_max;
>         union {
>                 unsigned long   bits[IO_BITMAP_LONGS];
> @@ -13,6 +15,9 @@ struct io_bitmap {
>         };
>  };
>
> +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(&current->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)
>         clear_thread_flag(TIF_IO_BITMAP);
>         tss_update_io_bitmap();
>         preempt_enable();
> -       kfree(iobm);
> +       if (iobm && refcount_dec_and_test(&iobm->refcnt))
> +               kfree(iobm);
>  }
>
>  /*
> @@ -59,8 +71,26 @@ long ksys_ioperm(unsigned long from, uns
>                         return -ENOMEM;
>
>                 memset(iobm->bits, 0xff, sizeof(iobm->bits));
> +               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;
> +               io_bitmap_exit();

And change the refcount to 1?

>         }
>

Otherwise:

Acked-by: Andy Lutomirski <luto@kernel.org>

(I'm about to send, and I see PeterZ beat me to the punch.  You can
still have the ack, though.)

  parent reply	other threads:[~2019-11-12 18:12 UTC|newest]

Thread overview: 57+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-11-11 22:03 [patch V2 00/16] x86/iopl: Prevent user space from using CLI/STI with iopl(3) Thomas Gleixner
2019-11-11 22:03 ` [patch V2 01/16] x86/ptrace: Prevent truncation of bitmap size Thomas Gleixner
2019-11-12 15:34   ` Andy Lutomirski
2019-11-11 22:03 ` [patch V2 02/16] x86/process: Unify copy_thread_tls() Thomas Gleixner
2019-11-11 22:03 ` [patch V2 03/16] x86/cpu: Unify cpu_init() Thomas Gleixner
2019-11-11 22:03 ` [patch V2 04/16] x86/tss: Fix and move VMX BUILD_BUG_ON() Thomas Gleixner
2019-11-11 22:44   ` Paolo Bonzini
2019-11-12 15:37   ` Andy Lutomirski
2019-11-11 22:03 ` [patch V2 05/16] x86/iopl: Cleanup include maze Thomas Gleixner
2019-11-12 15:37   ` Andy Lutomirski
2019-11-11 22:03 ` [patch V2 06/16] x86/io: Speedup schedule out of I/O bitmap user Thomas Gleixner
2019-11-12 16:00   ` Andy Lutomirski
2019-11-12 17:08     ` Thomas Gleixner
2019-11-11 22:03 ` [patch V2 07/16] x86/ioperm: Move iobitmap data into a struct Thomas Gleixner
2019-11-12 16:02   ` Andy Lutomirski
2019-11-12 17:08     ` Thomas Gleixner
2019-11-11 22:03 ` [patch V2 08/16] x86/ioperm: Add bitmap sequence number Thomas Gleixner
2019-11-12  9:22   ` Peter Zijlstra
2019-11-12  9:55     ` [patch V2 08/16] x86/ioperm: Add bitmap sequence numberc Thomas Gleixner
2019-11-12 16:08   ` [patch V2 08/16] x86/ioperm: Add bitmap sequence number Andy Lutomirski
2019-11-12 17:10     ` Thomas Gleixner
2019-11-11 22:03 ` [patch V2 09/16] x86/ioperm: Move TSS bitmap update to exit to user work Thomas Gleixner
2019-11-12 16:16   ` Andy Lutomirski
2019-11-12 17:20     ` Thomas Gleixner
2019-11-12 17:41       ` Andy Lutomirski
2019-11-12 17:46         ` Linus Torvalds
2019-11-13  8:30           ` Peter Zijlstra
2019-11-11 22:03 ` [patch V2 10/16] x86/ioperm: Remove bitmap if all permissions dropped Thomas Gleixner
2019-11-12 17:43   ` Andy Lutomirski
2019-11-11 22:03 ` [patch V2 11/16] x86/ioperm: Share I/O bitmap if identical Thomas Gleixner
2019-11-12  7:14   ` Ingo Molnar
2019-11-12  7:17     ` Thomas Gleixner
2019-11-12  7:52       ` Ingo Molnar
2019-11-12  9:15   ` Peter Zijlstra
2019-11-12  9:51     ` Thomas Gleixner
2019-11-14 11:02     ` David Laight
2019-11-14 12:39       ` Thomas Gleixner
2019-11-14 13:09       ` Peter Zijlstra
2019-11-14 13:22         ` David Laight
2019-11-12 18:12   ` Andy Lutomirski [this message]
2019-11-11 22:03 ` [patch V2 12/16] selftests/x86/ioperm: Extend testing so the shared bitmap is exercised Thomas Gleixner
2019-11-11 22:03 ` [patch V2 13/16] x86/iopl: Fixup misleading comment Thomas Gleixner
2019-11-12 18:14   ` Andy Lutomirski
2019-11-11 22:03 ` [patch V2 14/16] x86/iopl: Restrict iopl() permission scope Thomas Gleixner
2019-11-11 23:03   ` Thomas Gleixner
2019-11-12  6:32     ` Ingo Molnar
2019-11-12  8:42   ` Ingo Molnar
2019-11-12 10:07     ` Thomas Gleixner
2019-11-12 18:35   ` Andy Lutomirski
2019-11-11 22:03 ` [patch V2 15/16] x86/iopl: Remove legacy IOPL option Thomas Gleixner
2019-11-12 18:37   ` Andy Lutomirski
2019-11-12 19:40     ` Thomas Gleixner
2019-11-11 22:03 ` [patch V2 16/16] selftests/x86/iopl: Extend test to cover IOPL emulation Thomas Gleixner
2019-11-12  7:40 ` [PATCH] x86/iopl: Factor out IO-bitmap related TSS fields into 'struct x86_io_bitmap' Ingo Molnar
2019-11-12  7:59   ` [PATCH] x86/iopl: Harmonize 'struct io_bitmap' and 'struct x86_io_bitmap' nomenclature Ingo Molnar
2019-11-12  8:11   ` [PATCH] x86/iopl: Clear up the role of the two bitmap copying fields Ingo Molnar
2019-11-12  8:15   ` [PATCH] x86/iopl: Rename <asm/iobitmap.h> to <asm/io_bitmap.h> Ingo Molnar

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