linux-kernel - Re: [PATCHv3 07/17] x86/mm: Preserve KeyID on pte_modify() and pgprot

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Message-ID: <20180615204512.axt2avr4ysc2iyrp@black.fi.intel.com>
Date:   Fri, 15 Jun 2018 23:45:12 +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 07/17] x86/mm: Preserve KeyID on pte_modify() and
 pgprot_modify()

On Fri, Jun 15, 2018 at 04:58:24PM +0000, Dave Hansen wrote:
> On 06/15/2018 09:06 AM, Kirill A. Shutemov wrote:
> > I have no idea what such concept should be called. I cannot come with
> > anything better than PTE_PFN_MASK_MAX. Do you?
> 
> PTE_PRESERVE_MASK
> 
> Or maybe:
> 
> PTE_MODIFY_PRESERVE_MASK

It just replacing one confusion with another. Preserve what? How does it
differ from _PAGE_CHG_MASK?

I frankly think my name proposal convey more meaning.

> Maybe a comment to go along with it:
> 
> /*
>  * These are the bits that must be preserved during when doing a
>  * PTE permission modification operation, like taking a PTE from
>  * R/W->R/O.  They include the physical address and the memory
>  * encryption keyID.  The paddr and the keyID never occupy the same
>  * bits at the same time.  But, a given bit might be used for the keyID
>  * on one system and used for the physical address on another.  As an
>  * optimization, we manage them in one unit here since their combination
>  * always occupies the same hardware bits.
>  */

Thanks, this is useful.

-- 
 Kirill A. Shutemov