linux-kernel - Re: proposal for meltdown-workaround with low overhead

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Message-ID: <CA+8MBbL_hW-RTqh2umb-u3nzo7P8B65=p+rhzjrTGrmtFe18Eg@mail.gmail.com>
Date:   Thu, 4 Jan 2018 15:09:28 -0800
From:   Tony Luck <tony.luck@...il.com>
To:     Alexander Kleinsorge <aleks@...sik.tu-berlin.de>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: proposal for meltdown-workaround with low overhead

On Thu, Jan 4, 2018 at 11:45 AM, Alexander Kleinsorge
<aleks@...sik.tu-berlin.de> wrote:
> As Meltdown-Issue depends on allowing to cause many exceptions (usually :
> accessing an invalid address), we could restrict this misusage easy.

The accesses to the invalid address are performed speculatively by the CPU in
a code branch that is later found to be not taken. Hence there are no exceptions
at all.

-Tony