linux-kernel - Re: [PATCH v2 10/39] x86/mm: Introduce _PAGE

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Message-ID: <Yz1rbqGHOzmu8Hig@hirez.programming.kicks-ass.net>
Date:   Wed, 5 Oct 2022 13:33:02 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Rick Edgecombe <rick.p.edgecombe@...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>,
        Borislav Petkov <bp@...en8.de>,
        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>,
        Randy Dunlap <rdunlap@...radead.org>,
        "Ravi V . Shankar" <ravi.v.shankar@...el.com>,
        Weijiang Yang <weijiang.yang@...el.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        joao.moreira@...el.com, John Allen <john.allen@....com>,
        kcc@...gle.com, eranian@...gle.com, rppt@...nel.org,
        jamorris@...ux.microsoft.com, dethoma@...rosoft.com,
        Yu-cheng Yu <yu-cheng.yu@...el.com>
Subject: Re: [PATCH v2 10/39] x86/mm: Introduce _PAGE_COW

On Thu, Sep 29, 2022 at 03:29:07PM -0700, Rick Edgecombe wrote:

Mucho confusion here:

> (a) (Write=0,Cow=1,Dirty=0) A modified, copy-on-write (COW) page.
> (b) (Write=0,Cow=1,Dirty=0) A R/O page that has been COW'ed. The user page
> (d) (Write=0,Cow=1,Dirty=0) A shared shadow stack PTE. When a shadow stack

are all identical cases;

> (c) (Write=0,Cow=0,Dirty=1) A shadow stack PTE.
> (e) (Write=0,Cow=0,Dirty=1) A Cow PTE created when a processor without

as are these.