linux-kernel - Re: [PATCH 0/3] arch/x86: Optionally flush L1D on context switch

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Message-ID: <31c9720eff18ce167378e9a0017dcd73e0552164.camel@amazon.com>
Date:   Thu, 2 Apr 2020 20:35:46 +0000
From:   "Singh, Balbir" <sblbir@...zon.com>
To:     "jpoimboe@...hat.com" <jpoimboe@...hat.com>
CC:     "tglx@...utronix.de" <tglx@...utronix.de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "tony.luck@...el.com" <tony.luck@...el.com>,
        "keescook@...omium.org" <keescook@...omium.org>,
        "benh@...nel.crashing.org" <benh@...nel.crashing.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "dave.hansen@...el.com" <dave.hansen@...el.com>
Subject: Re: [PATCH 0/3] arch/x86: Optionally flush L1D on context switch

On Thu, 2020-04-02 at 15:13 -0500, Josh Poimboeuf wrote:
> CAUTION: This email originated from outside of the organization. Do not
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> 
> 
> On Thu, Apr 02, 2020 at 05:23:58PM +1100, Balbir Singh wrote:
> > Provide a mechanisn to flush the L1D cache on context switch.  The goal
> > is to allow tasks that are paranoid due to the recent snoop assisted data
> > sampling vulnerabilites, to flush their L1D on being switched out.
> 
> Hi Balbir,
> 
> Just curious, is it really vulnerabilities, plural?  I thought there was
> only one: CVE-2020-0550 (Snoop-assisted L1 Data Sampling).
> 
> (There was a similar one without the "snoop": L1D Eviction Sampling, but
> it's supposed to get fixed in microcode).
> 

Hi, Josh

Yes, that CVE the motivation, the mitigation for CVE-2020-0550 does suggest
flushing the cache on context switch. But in general, as we begin to find more
ways of evicting data or snopping data, a generic mechanism is more useful and
that is why I am making it an opt-in.

Balbir Singh.