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Subject: Re: [PATCH 00/45] arm Spectre fix backport review for LTS 4.9
To:     Will Deacon <will.deacon@arm.com>
Cc:     Greg KH <greg@kroah.com>, Marc Zyngier <marc.zyngier@arm.com>,
        Ard Biesheuvel <ard.biesheuvel@linaro.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        stable@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        linux-kernel@vger.kernel.org
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From:   Alex Shi <alex.shi@linaro.org>
Message-ID: <f12aee2c-556b-f146-17eb-707bb901dbd8@linaro.org>
Date:   Sat, 3 Mar 2018 08:54:10 +0800
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On 03/02/2018 06:30 PM, Will Deacon wrote:
> On Fri, Mar 02, 2018 at 05:02:32PM +0800, Alex Shi wrote:
>> As testing the spectre bug fix, that's a good question. I also asked
>> this question to original patch authors, like Marc. They said they just
>> figure out these patches could block spectre or meltdown issue. From my
>> side, I just reproduced the process internal spectre. But all fix on arm
>> can not resolve the user space internal spectre. It can block from user
>> to kernel or kernel to user spectre according the code purose. So I
>> believe these patch could do their job. And arm cpu would drop the
>> spectre branches if it has 20+ 'nop' instructions...
> 
> Since this is archived on a public list and I don't want people to rely on
> this, no, you cannot rely on "20+ 'nop' instructions" to work around
> spectre on arm/arm64. It might prevent a particular PoC working on a
> particular SoC, but it's fragile at best.
> 


Thanks for comments, Will!

Yes, I full understand the difference between SoCs. Thanks for point it out!


Regards
Alex