linux-kernel - Re: [PATCH, RFC 03/62] mm/ksm: Do not merge pages with different KeyIDs

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Message-ID: <20190513142739.7v3cnrnnnsdldcuc@black.fi.intel.com>
Date:   Mon, 13 May 2019 17:27:39 +0300
From:   "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, x86@...nel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, Borislav Petkov <bp@...en8.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...capital.net>,
        David Howells <dhowells@...hat.com>,
        Kees Cook <keescook@...omium.org>,
        Kai Huang <kai.huang@...ux.intel.com>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        Alison Schofield <alison.schofield@...el.com>,
        linux-mm@...ck.org, kvm@...r.kernel.org, keyrings@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH, RFC 03/62] mm/ksm: Do not merge pages with different
 KeyIDs

On Fri, May 10, 2019 at 06:07:11PM +0000, Dave Hansen wrote:
> On 5/8/19 7:43 AM, Kirill A. Shutemov wrote:
> > KeyID indicates what key to use to encrypt and decrypt page's content.
> > Depending on the implementation a cipher text may be tied to physical
> > address of the page. It means that pages with an identical plain text
> > would appear different if KSM would look at a cipher text. It effectively
> > disables KSM for encrypted pages.
> > 
> > In addition, some implementations may not allow to read cipher text at all.
> > 
> > KSM compares plain text instead (transparently to KSM code).
> > 
> > But we still need to make sure that pages with identical plain text will
> > not be merged together if they are encrypted with different keys.
> > 
> > To make it work kernel only allows merging pages with the same KeyID.
> > The approach guarantees that the merged page can be read by all users.
> 
> I can't really parse this description.  Can I suggest replacement text?

Sure.

-- 
 Kirill A. Shutemov