linux-kernel - Re: [PATCHv5 08/19] x86/mm: Introduce variables to store number, shift and mask of KeyIDs

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Date:   Thu, 19 Jul 2018 07:23:27 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     "Kirill A. Shutemov" <kirill@...temov.name>
Cc:     "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>,
        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 08/19] x86/mm: Introduce variables to store number,
 shift and mask of KeyIDs

On 07/19/2018 03:21 AM, Kirill A. Shutemov wrote:
> On Wed, Jul 18, 2018 at 04:19:10PM -0700, Dave Hansen wrote:
>> On 07/17/2018 04:20 AM, Kirill A. Shutemov wrote:
>>> mktme_nr_keyids holds number of KeyIDs available for MKTME, excluding
>>> KeyID zero which used by TME. MKTME KeyIDs start from 1.
>>>
>>> mktme_keyid_shift holds shift of KeyID within physical address.
>> I know what all these words mean, but the combination of them makes no
>> sense to me.  I still don't know what the variable does after reading this.
>>
>> Is this the lowest bit in the physical address which is used for the
>> KeyID?  How many bits you must shift up a KeyID to get to the location
>> at which it can be masked into the physical address?
> Right.
> 
> I'm not sure what is not clear from the description. It look fine to me.

Well, OK, I guess I can write a better one for you.

"Position in the PTE of the lowest bit of the KeyID"

It's also a name that could use some love (now that I know what it
does).  mktme_keyid_pte_shift would be much better.  Or
mktme_keyid_low_pte_bit.