linux-kernel - Re: [PATCHv3 03/17] mm/ksm: Do not merge pages with different KeyIDs

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Message-ID: <20180613203108.k63fda4hvsqyczw7@black.fi.intel.com>
Date:   Wed, 13 Jun 2018 23:31:08 +0300
From:   "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        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: [PATCHv3 03/17] mm/ksm: Do not merge pages with different KeyIDs

On Wed, Jun 13, 2018 at 05:51:50PM +0000, Dave Hansen wrote:
> On 06/12/2018 07:39 AM, Kirill A. Shutemov wrote:
> > Pages encrypted with different encryption keys are not subject to KSM
> > merge. Otherwise it would cross security boundary.
> 
> This needs a much stronger explanation.

Okay, fair enough.

> Which KeyID would be used for access in the new direct mappings?

New direct mapping?

Pages would be compared using direct mappings relevant for their KeyID.
They will be threated as identical if they plain-text is identical.

> What actually happens without this patch in place?

One of processes would get the page mapped with wrong KeyID and see
garbage. We setup mapping according to KeyID in vma->vm_page_prot.

-- 
 Kirill A. Shutemov