linux-kernel - Re: [PATCH v24 16/30] mm: Fixup places that call pte

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Date:   Fri, 9 Apr 2021 18:20:09 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     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>,
        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>,
        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>,
        Haitao Huang <haitao.huang@...el.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: Re: [PATCH v24 16/30] mm: Fixup places that call pte_mkwrite()
 directly

On Thu, Apr 01, 2021 at 03:10:50PM -0700, Yu-cheng Yu wrote:
> When serving a page fault, maybe_mkwrite() makes a PTE writable if it is in
> a writable vma.  A shadow stack vma is writable, but its PTEs need
> _PAGE_DIRTY to be set to become writable.  For this reason, maybe_mkwrite()
> has been updated.
> 
> There are a few places that call pte_mkwrite() directly, but have the
> same result as from maybe_mkwrite().  These sites need to be updated for
> shadow stack as well.  Thus, change them to maybe_mkwrite():
> 
> - do_anonymous_page() and migrate_vma_insert_page() check VM_WRITE directly
>   and call pte_mkwrite(), which is the same as maybe_mkwrite().  Change
>   them to maybe_mkwrite().
> 
> - In do_numa_page(), if the numa entry was writable, then pte_mkwrite()
>   is called directly.  Fix it by doing maybe_mkwrite().
> 
> - In change_pte_range(), pte_mkwrite() is called directly.  Replace it with
>   maybe_mkwrite().
> 
>   A shadow stack vma is writable but has different vma
> flags, and handled accordingly in maybe_mkwrite().
> 

Have you checked THP side? Looks like at least do_huge_pmd_numa_page()
needs adjustment, no?

-- 
 Kirill A. Shutemov