linux-kernel - Re: [PATCHv5 03/19] mm/ksm: Do not merge pages with different KeyIDs

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Date:   Wed, 18 Jul 2018 10:38:27 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Tom Lendacky <thomas.lendacky@....com>
Cc:     Kai Huang <kai.huang@...ux.intel.com>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCHv5 03/19] mm/ksm: Do not merge pages with different KeyIDs

On 07/17/2018 04:20 AM, Kirill A. Shutemov wrote:
> Pages encrypted with different encryption keys are not allowed to be
> merged by KSM. Otherwise it would cross security boundary.

Let's say I'm using plain AES (not AES-XTS).  I use the same key in two
keyid slots.  I map a page with the first keyid and another with the
other keyid.

Won't they have the same cipertext?  Why shouldn't we KSM them?