Re: [RFC PATCH] asm/generic: introduce if_nospec and nospec_barrier

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To: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Subject: Re: [RFC PATCH] asm/generic: introduce if_nospec and nospec_barrier
From: Alan Cox <gnomes@xxxxxxxxxxxxxxxxxxx>
Date: Thu, 4 Jan 2018 23:11:37 +0000
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>, Pavel Machek <pavel@xxxxxx>, Julia Lawall <julia.lawall@xxxxxxx>, Linux Kernel Mailing List <linux-kernel@xxxxxxxxxxxxxxx>, Mark Rutland <mark.rutland@xxxxxxx>, linux-arch@xxxxxxxxxxxxxxx, Peter Zijlstra <peterz@xxxxxxxxxxxxx>, Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx>, Thomas Gleixner <tglx@xxxxxxxxxxxxx>, Elena Reshetova <elena.reshetova@xxxxxxxxx>, Alan Cox <alan@xxxxxxxxxxxxxxx>, Dan Carpenter <dan.carpenter@xxxxxxxxxx>
In-reply-to: <CA+55aFxNqWQcMQmpbsRhhfb7M8ch30627AkEsswaNk-=MvZo5w@mail.gmail.com>
Organization: Intel Corporation
References: <20180103223827.39601-1-mark.rutland@arm.com> <151502463248.33513.5960736946233335087.stgit@dwillia2-desk3.amr.corp.intel.com> <CA+55aFzSYExr33w849=3o+2XGr9pUKpFucc5p-kKbEy20VVLPA@mail.gmail.com> <20180104010754.22ca6a74@alans-desktop> <CAPcyv4ge14OPyfoQvXHLyXwqX7cjWvm4DouUOc=WrNo1Lr9Qyw@mail.gmail.com> <alpine.DEB.2.20.1801040728140.2148@hadrien> <CAPcyv4gLcC7vsxLUCEJdEvDRf4AhgF0x1fpTEcH7AOe=kuNfoQ@mail.gmail.com> <20180104192648.GA10427@amd> <CAPcyv4g0ZEP_LuXwsf1rJGaG65UHn5sj=DMyMdCnzKD9T-vnyg@mail.gmail.com> <CA+55aFwRh++2cyfi1ZXnWCwGv=kuSjft-RcSCDW89T5g=0RB2Q@mail.gmail.com> <20180104225515.13a40f0f@alans-desktop> <CA+55aFxNqWQcMQmpbsRhhfb7M8ch30627AkEsswaNk-=MvZo5w@mail.gmail.com>

> It's also possible that x86 'lfence' really is so fast that it doesn't
> make sense to try to do this.

If you've got a lot going on it's not 1 cycle.

Alan

References:
- [RFC PATCH 0/4] API for inhibiting speculative arbitrary read primitives
  - From: Mark Rutland
- [RFC PATCH] asm/generic: introduce if_nospec and nospec_barrier
  - From: Dan Williams
- Re: [RFC PATCH] asm/generic: introduce if_nospec and nospec_barrier
  - From: Linus Torvalds
- Re: [RFC PATCH] asm/generic: introduce if_nospec and nospec_barrier
  - From: Alan Cox
- Re: [RFC PATCH] asm/generic: introduce if_nospec and nospec_barrier
  - From: Dan Williams
- Re: [RFC PATCH] asm/generic: introduce if_nospec and nospec_barrier
  - From: Julia Lawall
- Re: [RFC PATCH] asm/generic: introduce if_nospec and nospec_barrier
  - From: Dan Williams
- Re: [RFC PATCH] asm/generic: introduce if_nospec and nospec_barrier
  - From: Pavel Machek
- Re: [RFC PATCH] asm/generic: introduce if_nospec and nospec_barrier
  - From: Dan Williams
- Re: [RFC PATCH] asm/generic: introduce if_nospec and nospec_barrier
  - From: Linus Torvalds
- Re: [RFC PATCH] asm/generic: introduce if_nospec and nospec_barrier
  - From: Alan Cox
- Re: [RFC PATCH] asm/generic: introduce if_nospec and nospec_barrier
  - From: Linus Torvalds

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