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

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Date:   Wed, 13 Jun 2018 13:35:46 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.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 06/13/2018 01:31 PM, Kirill A. Shutemov wrote:
>> What actually happens without this patch in place?
> 
> One of processes would get the page mapped with wrong KeyID and see
> garbage. 

OK, but what about two pages with the same KeyID?  It's actually totally
possible for KSM to determine that two pages have the same plaintext and
merge them.  Why don't we do that?

> We setup mapping according to KeyID in vma->vm_page_prot.

Then why do we bother with page_keyid() and the page_ext stuff?