linux-kernel - Re: [PATCH v15 06/26] x86/mm: Change _PAGE_DIRTY to _PAGE_DIRTY

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Message-ID: <93eb0255-df5c-5cb3-654f-e74c1af956b2@intel.com>
Date:   Thu, 3 Dec 2020 07:12:11 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     Borislav Petkov <bp@...en8.de>, Yu-cheng Yu <yu-cheng.yu@...el.com>
Cc:     x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-mm@...ck.org,
        linux-arch@...r.kernel.org, linux-api@...r.kernel.org,
        Arnd Bergmann <arnd@...db.de>,
        Andy Lutomirski <luto@...nel.org>,
        Balbir Singh <bsingharora@...il.com>,
        Cyrill Gorcunov <gorcunov@...il.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Eugene Syromiatnikov <esyr@...hat.com>,
        Florian Weimer <fweimer@...hat.com>,
        "H.J. Lu" <hjl.tools@...il.com>, Jann Horn <jannh@...gle.com>,
        Jonathan Corbet <corbet@....net>,
        Kees Cook <keescook@...omium.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Nadav Amit <nadav.amit@...il.com>,
        Oleg Nesterov <oleg@...hat.com>, Pavel Machek <pavel@....cz>,
        Peter Zijlstra <peterz@...radead.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Vedvyas Shanbhogue <vedvyas.shanbhogue@...el.com>,
        Dave Martin <Dave.Martin@....com>,
        Weijiang Yang <weijiang.yang@...el.com>,
        Pengfei Xu <pengfei.xu@...el.com>
Subject: Re: [PATCH v15 06/26] x86/mm: Change _PAGE_DIRTY to _PAGE_DIRTY_HW

On 12/3/20 1:19 AM, Borislav Petkov wrote:
> On Tue, Nov 10, 2020 at 08:21:51AM -0800, Yu-cheng Yu wrote:
>> Before introducing _PAGE_COW for non-hardware memory management purposes in
>> the next patch, rename _PAGE_DIRTY to _PAGE_DIRTY_HW and _PAGE_BIT_DIRTY to
>> _PAGE_BIT_DIRTY_HW to make meanings more clear.  There are no functional
>> changes from this patch.
> There's no guarantee for "next" or "this" patch when a patch gets
> applied so reword your commit message pls.
> 
> Also, I fail to understand here what _PAGE_DIRTY_HW makes more clear?
> The page dirty bit is clear enough to me so why the churn?

Once upon a time in this set, we had:

	_PAGE_DIRTY	(the old hardware bit)
and
	_PAGE_DIRTY_SW	(the new shadow stack necessitated bit)

In *that* case, it made sense to change the name of the hardware one to
help differentiate them.  But, over time, we changed _PAGE_DIRTY_SW to
_PAGE_COW.

I think you're right.  The renaming is just churn now with the current
naming.