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

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Date:   Mon, 14 Jan 2019 06:39:33 -0800
From:   Arjan van de Ven <arjan@...ux.intel.com>
To:     Jiri Kosina <jikos@...nel.org>, 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>,
        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 1/14/2019 5:06 AM, Jiri Kosina wrote:
> 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.

assuming L1D is not shared between SMT threads obviously :)

>