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From: Andy Lutomirski <luto@kernel.org>
To: Nadav Amit <namit@vmware.com>
Cc: Ingo Molnar <mingo@redhat.com>, Andy Lutomirski <luto@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Josh Poimboeuf <jpoimboe@redhat.com>,
	Edward Cree <ecree@solarflare.com>,
	"H . Peter Anvin" <hpa@zytor.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	LKML <linux-kernel@vger.kernel.org>,
	Nadav Amit <nadav.amit@gmail.com>, X86 ML <x86@kernel.org>,
	Paolo Abeni <pabeni@redhat.com>, Borislav Petkov <bp@alien8.de>,
	David Woodhouse <dwmw@amazon.co.uk>
Subject: Re: [RFC v2 1/6] x86: introduce kernel restartable sequence
Date: Mon, 31 Dec 2018 12:08:15 -0800
Message-ID: <CALCETrXqdgqYgsKd0xR7RMvVvotu1u==+n3gYyDgTZvbvmJ5VQ@mail.gmail.com> (raw)
In-Reply-To: <20181231072112.21051-2-namit@vmware.com>

On Sun, Dec 30, 2018 at 11:20 PM Nadav Amit <namit@vmware.com> wrote:
>
> It is sometimes beneficial to have a restartable sequence - very few
> instructions which if they are preempted jump to a predefined point.
>
> To provide such functionality on x86-64, we use an empty REX-prefix
> (opcode 0x40) as an indication for instruction in such a sequence. Before
> calling the schedule IRQ routine, if the "magic" prefix is found, we
> call a routine to adjust the instruction pointer.  It is expected that
> this opcode is not in common use.
>
> The following patch will make use of this function. Since there are no
> other users (yet?), the patch does not bother to create a general
> infrastructure and API that others can use for such sequences. Yet, it
> should not be hard to make such extension later.

The following patch does not use it.  Can you update this?


> +asmlinkage __visible void restart_kernel_rseq(struct pt_regs *regs)
> +{
> +       if (user_mode(regs) || *(u8 *)regs->ip != KERNEL_RESTARTABLE_PREFIX)
> +               return;

else?

I suspect something is missing here.  Or I'm very confused.

> +}

  reply index

Thread overview: 42+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-12-31  7:21 [RFC v2 0/6] x86: dynamic indirect branch promotion Nadav Amit
2018-12-31  7:21 ` [RFC v2 1/6] x86: introduce kernel restartable sequence Nadav Amit
2018-12-31 20:08   ` Andy Lutomirski [this message]
2018-12-31 21:12     ` Nadav Amit
2019-01-03 22:21   ` Andi Kleen
2019-01-03 22:29     ` Nadav Amit
2019-01-03 22:48       ` Andi Kleen
2019-01-03 22:52         ` Nadav Amit
2019-01-03 23:40           ` Andi Kleen
2019-01-03 23:56             ` Nadav Amit
2019-01-04  0:34   ` hpa
2018-12-31  7:21 ` [RFC v2 2/6] objtool: ignore instructions Nadav Amit
2018-12-31  7:21 ` [RFC v2 3/6] x86: patch indirect branch promotion Nadav Amit
2018-12-31  7:21 ` [RFC v2 4/6] x86: interface for accessing indirect branch locations Nadav Amit
2018-12-31  7:21 ` [RFC v2 5/6] x86: learning and patching indirect branch targets Nadav Amit
2018-12-31 20:05   ` Andy Lutomirski
2018-12-31 21:07     ` Nadav Amit
2018-12-31  7:21 ` [RFC v2 6/6] x86: outline optpoline Nadav Amit
2018-12-31 19:51 ` [RFC v2 0/6] x86: dynamic indirect branch promotion Andy Lutomirski
2018-12-31 19:53   ` Nadav Amit
2019-01-03 18:10     ` Josh Poimboeuf
2019-01-03 18:30       ` Nadav Amit
2019-01-03 20:31         ` Josh Poimboeuf
2019-01-03 22:18 ` Andi Kleen
2019-01-07 16:32   ` Peter Zijlstra
2019-01-08  7:47     ` Adrian Hunter
2019-01-08  9:25       ` Peter Zijlstra
2019-01-08 10:01         ` Adrian Hunter
2019-01-08 10:10           ` Peter Zijlstra
2019-01-08 17:27             ` Andi Kleen
2019-01-08 18:28               ` Nadav Amit
2019-01-08 19:01                 ` Peter Zijlstra
2019-01-08 20:47                   ` Nadav Amit
2019-01-08 20:53                     ` Andi Kleen
2019-01-09 10:35                     ` Peter Zijlstra
2019-08-29  8:23                       ` Tracing text poke / kernel self-modifying code (Was: Re: [RFC v2 0/6] x86: dynamic indirect branch promotion) Adrian Hunter
2019-08-29  8:53                         ` Peter Zijlstra
2019-08-29  9:40                           ` Adrian Hunter
2019-08-29 11:46                             ` Peter Zijlstra
2019-09-12  7:00                               ` Adrian Hunter
2019-09-12 12:17                                 ` hpa
2019-01-08 18:57               ` [RFC v2 0/6] x86: dynamic indirect branch promotion Peter Zijlstra

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