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Subject: Re: [PATCH v14 1/7] x86/cet/ibt: Add Kconfig option for user-mode
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To:     Cyrill Gorcunov <gorcunov@gmail.com>
Cc:     x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, linux-kernel@vger.kernel.org,
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        linux-arch@vger.kernel.org, linux-api@vger.kernel.org,
        Arnd Bergmann <arnd@arndb.de>,
        Andy Lutomirski <luto@kernel.org>,
        Balbir Singh <bsingharora@gmail.com>,
        Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Eugene Syromiatnikov <esyr@redhat.com>,
        Florian Weimer <fweimer@redhat.com>,
        "H.J. Lu" <hjl.tools@gmail.com>, Jann Horn <jannh@google.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Kees Cook <keescook@chromium.org>,
        Mike Kravetz <mike.kravetz@oracle.com>,
        Nadav Amit <nadav.amit@gmail.com>,
        Oleg Nesterov <oleg@redhat.com>, Pavel Machek <pavel@ucw.cz>,
        Peter Zijlstra <peterz@infradead.org>,
        Randy Dunlap <rdunlap@infradead.org>,
        "Ravi V. Shankar" <ravi.v.shankar@intel.com>,
        Vedvyas Shanbhogue <vedvyas.shanbhogue@intel.com>,
        Dave Martin <Dave.Martin@arm.com>,
        Weijiang Yang <weijiang.yang@intel.com>,
        Pengfei Xu <pengfei.xu@intel.com>
References: <20201012154530.28382-1-yu-cheng.yu@intel.com>
 <20201012154530.28382-2-yu-cheng.yu@intel.com> <20201012191511.GC14048@grain>
From:   "Yu, Yu-cheng" <yu-cheng.yu@intel.com>
Message-ID: <c1bb9728-95a8-2fc2-6a28-ea37f2b50e7b@intel.com>
Date:   Mon, 12 Oct 2020 13:29:57 -0700
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On 10/12/2020 12:15 PM, Cyrill Gorcunov wrote:
> On Mon, Oct 12, 2020 at 08:45:24AM -0700, Yu-cheng Yu wrote:
> ...
>> +	  the application support it.  When this feature is enabled,
>> +	  legacy non-IBT applications continue to work, but without
>> +	  IBT protection.
>> +	  Support for this feature is only known to be present on
>> +	  processors released in 2020 or later.  CET features are also
>> +	  known to increase kernel text size by 3.7 KB.
> 
> It seems the last sentence is redundant - new features always bloat
> the kernel code and precise size may differ depending on compiler
> and options. Surely this can be patched on top.
> 

This was added after some discussion in v12 about kernel text size [1]. 
I think these few extra words can help people who have older machines 
and want to save some space.  Yes, like you said, if later we don't want 
this sentence, I will be happy to add a patch to remove it.  Thanks for 
the feedback.

Yu-cheng

[1] 
https://lore.kernel.org/linux-api/5e0a4005-45e3-3e88-e6e0-4ec31aad7eb9@intel.com/