linux-kernel - Re: [PATCH v28 09/32] x86/mm: Introduce _PAGE

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Message-ID: <YSEpcQG7WEa8hl9c@zn.tnic>
Date:   Sat, 21 Aug 2021 18:27:29 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     "Yu, Yu-cheng" <yu-cheng.yu@...el.com>
Cc:     Andy Lutomirski <luto@...nel.org>,
        "luto@...capital.net" <luto@...capital.net>,
        the arch/x86 maintainers <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-doc@...r.kernel.org, linux-mm@...ck.org,
        linux-arch@...r.kernel.org, Linux API <linux-api@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>,
        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 (Intel)" <peterz@...radead.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        "Shankar, Ravi V" <ravi.v.shankar@...el.com>,
        Dave Martin <Dave.Martin@....com>,
        Weijiang Yang <weijiang.yang@...el.com>,
        Pengfei Xu <pengfei.xu@...el.com>,
        Haitao Huang <haitao.huang@...el.com>,
        Rick P Edgecombe <rick.p.edgecombe@...el.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: Re: [PATCH v28 09/32] x86/mm: Introduce _PAGE_COW

On Wed, Aug 18, 2021 at 09:38:30AM -0700, Yu, Yu-cheng wrote:
> We can visualize the type of a mm area by looking at vma->vm_flags, e.g.

visualize?

> maybe_mkwrite(), and PTE macros as lower-level operatives.  These two have
> some relations but not one-to-one.  Note that a PTE in a writable area is
> not always pte_write().
> 
> I have considered and implemented a shadow stack PTE either pte_write() or
> not.  Making shadow stack as pte_write() results in less arch_* macros and
> less confusion in copy-on-write code.  That is one more thing to consider.

Ok, even though I'm still not 100% convinced by both amluto's and your
arguments. Let's try it and see what happens...

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette