linux-kernel - Re: [PATCH] x86/speculation: Add document to describe Spectre and its mitigations

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Date:   Mon, 14 Jan 2019 14:06:19 +0100 (CET)
From:   Jiri Kosina <jikos@...nel.org>
To:     Pavel Machek <pavel@....cz>
cc:     Tim Chen <tim.c.chen@...ux.intel.com>,
        Jonathan Corbet <corbet@....net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Tom Lendacky <thomas.lendacky@....com>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        David Woodhouse <dwmw@...zon.co.uk>,
        Andi Kleen <ak@...ux.intel.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Asit Mallick <asit.k.mallick@...el.com>,
        Arjan van de Ven <arjan@...ux.intel.com>,
        Jon Masters <jcm@...hat.com>,
        Waiman Long <longman9394@...il.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        Borislav Petkov <bp@...en8.de>, linux-kernel@...r.kernel.org,
        x86@...nel.org, stable@...r.kernel.org
Subject: Re: [PATCH] x86/speculation: Add document to describe Spectre and
 its mitigations

On Mon, 14 Jan 2019, Pavel Machek wrote:

> Frankly I'd not call it Meltdown, as it works only on data in the cache, 
> so the defense is completely different. Seems more like a l1tf
> :-).

Meltdown on x86 also seems to work only for data in L1D, but the pipeline 
could be constructed in a way that data are actually fetched into L1D 
before speculation gives up, which is not the case on ppc (speculation 
aborts on L2->L1 propagation IIRC). That's why flushing L1D on ppc is 
sufficient, but on x86 it's not.

-- 
Jiri Kosina
SUSE Labs