From: Thomas Gleixner <tglx@linutronix.de>
To: Peter Zijlstra <peterz@infradead.org>
Cc: LKML <linux-kernel@vger.kernel.org>,
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>,
Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [patch V2 08/16] x86/ioperm: Add bitmap sequence numberc
Date: Tue, 12 Nov 2019 10:55:24 +0100 (CET) [thread overview]
Message-ID: <alpine.DEB.2.21.1911121051490.1833@nanos.tec.linutronix.de> (raw)
In-Reply-To: <20191112092246.GY4131@hirez.programming.kicks-ass.net>
On Tue, 12 Nov 2019, Peter Zijlstra wrote:
> On Mon, Nov 11, 2019 at 11:03:22PM +0100, Thomas Gleixner wrote:
> > Add a globally unique sequence number which is incremented when ioperm() is
> > changing the I/O bitmap of a task. Store the new sequence number in the
> > io_bitmap structure and compare it along with the actual struct pointer
> > with the one which was last loaded on a CPU. Only update the bitmap if
> > either of the two changes. That should further reduce the overhead of I/O
> > bitmap scheduling when there are only a few I/O bitmap users on the system.
>
> > + /* Update the sequence number to force an update in switch_to() */
> > + iobm->sequence = atomic64_add_return(1, &io_bitmap_sequence);
>
> > + if (tss->last_bitmap != iobm ||
> > + tss->last_sequence != iobm->sequence)
> > + switch_to_update_io_bitmap(tss, iobm);
>
> Initially I wondered why we need a globally unique sequence number if we
> already check the struct iobitmap pointer. That ought to make the
> sequence number per-object.
>
> However, that breaks for memory re-use. So yes, we need that thing to be
> global.
Actually with a global 64bit wide counter we can just avoid the pointer
comparison. Assumed a ioperm() syscall every nanosecond it takes about 584
years of uptime to wrap around. :)
Thanks,
tglx
next prev parent reply other threads:[~2019-11-12 9:55 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 ` Thomas Gleixner [this message]
2019-11-12 16:08 ` 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
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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