linux-kernel - Re: [PATCH v9 05/42] mm: Move VM_UFFD_MINOR

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Message-ID: <42a95041-e1a7-f343-8432-e2ce07af4e9e@redhat.com>
Date:   Wed, 14 Jun 2023 10:50:04 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Rick Edgecombe <rick.p.edgecombe@...el.com>, 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>,
        Weijiang Yang <weijiang.yang@...el.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        John Allen <john.allen@....com>, kcc@...gle.com,
        eranian@...gle.com, rppt@...nel.org, jamorris@...ux.microsoft.com,
        dethoma@...rosoft.com, akpm@...ux-foundation.org,
        Andrew.Cooper3@...rix.com, christina.schimpe@...el.com,
        debug@...osinc.com, szabolcs.nagy@....com,
        torvalds@...ux-foundation.org, broonie@...nel.org
Cc:     Yu-cheng Yu <yu-cheng.yu@...el.com>,
        Axel Rasmussen <axelrasmussen@...gle.com>,
        Peter Xu <peterx@...hat.com>, Pengfei Xu <pengfei.xu@...el.com>
Subject: Re: [PATCH v9 05/42] mm: Move VM_UFFD_MINOR_BIT from 37 to 38

On 13.06.23 02:10, Rick Edgecombe wrote:
> From: Yu-cheng Yu <yu-cheng.yu@...el.com>
> 
> The x86 Control-flow Enforcement Technology (CET) feature includes a new
> type of memory called shadow stack. This shadow stack memory has some
> unusual properties, which requires some core mm changes to function
> properly.
> 
> Future patches will introduce a new VM flag VM_SHADOW_STACK that will be
> VM_HIGH_ARCH_BIT_5. VM_HIGH_ARCH_BIT_1 through VM_HIGH_ARCH_BIT_4 are
> bits 32-36, and bit 37 is the unrelated VM_UFFD_MINOR_BIT. For the sake
> of order, make all VM_HIGH_ARCH_BITs stay together by moving
> VM_UFFD_MINOR_BIT from 37 to 38. This will allow VM_SHADOW_STACK to be
> introduced as 37.
> 
> Signed-off-by: Yu-cheng Yu <yu-cheng.yu@...el.com>
> Co-developed-by: Rick Edgecombe <rick.p.edgecombe@...el.com>
> Signed-off-by: Rick Edgecombe <rick.p.edgecombe@...el.com>
> Reviewed-by: Borislav Petkov (AMD) <bp@...en8.de>
> Reviewed-by: Kees Cook <keescook@...omium.org>
> Reviewed-by: Axel Rasmussen <axelrasmussen@...gle.com>
> Acked-by: Mike Rapoport (IBM) <rppt@...nel.org>
> Acked-by: Peter Xu <peterx@...hat.com>
> Tested-by: Pengfei Xu <pengfei.xu@...el.com>
> Tested-by: John Allen <john.allen@....com>
> Tested-by: Kees Cook <keescook@...omium.org>
> ---
>   include/linux/mm.h | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 9ec20cbb20c1..6f52c1e7c640 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -370,7 +370,7 @@ extern unsigned int kobjsize(const void *objp);
>   #endif
>   
>   #ifdef CONFIG_HAVE_ARCH_USERFAULTFD_MINOR
> -# define VM_UFFD_MINOR_BIT	37
> +# define VM_UFFD_MINOR_BIT	38
>   # define VM_UFFD_MINOR		BIT(VM_UFFD_MINOR_BIT)	/* UFFD minor faults */
>   #else /* !CONFIG_HAVE_ARCH_USERFAULTFD_MINOR */
>   # define VM_UFFD_MINOR		VM_NONE

Reviewed-by: David Hildenbrand <david@...hat.com>

-- 
Cheers,

David / dhildenb