linux-kernel - Re: [PATCH v27 13/31] mm: Move VM_UFFD_MINOR

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Date:   Fri, 21 May 2021 18:58:14 -0700
From:   "Yu, Yu-cheng" <yu-cheng.yu@...el.com>
To:     Axel Rasmussen <axelrasmussen@...gle.com>
Cc:     x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>, linux-doc@...r.kernel.org,
        Linux MM <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>,
        Peter Xu <peterx@...hat.com>
Subject: Re: [PATCH v27 13/31] mm: Move VM_UFFD_MINOR_BIT from 37 to 38

On 5/21/2021 3:25 PM, Axel Rasmussen wrote:
> This seems reasonable to me. The particular bit used isn't so
> important from my perspective. I can't think of a way this would break
> backward compatibility or such. So:
> 
> Reviewed-by: Axel Rasmussen <axelrasmussen@...gle.com>

Thanks!

Yu-cheng

> 
> On Fri, May 21, 2021 at 3:13 PM Yu-cheng Yu <yu-cheng.yu@...el.com> wrote:
>>
>> To introduce VM_SHADOW_STACK as VM_HIGH_ARCH_BIT (37), and make all
>> VM_HIGH_ARCH_BITs stay together, move VM_UFFD_MINOR_BIT from 37 to 38.
>>
>> Signed-off-by: Yu-cheng Yu <yu-cheng.yu@...el.com>
>> Cc: Axel Rasmussen <axelrasmussen@...gle.com>
>> Cc: Peter Xu <peterx@...hat.com>
>> Cc: Mike Kravetz <mike.kravetz@...cle.com>
>> ---
>>   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 c274f75efcf9..923f89b9f1b5 100644
>> --- a/include/linux/mm.h
>> +++ b/include/linux/mm.h
>> @@ -373,7 +373,7 @@ 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
>> --
>> 2.21.0
>>