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Date:   Fri, 12 Mar 2021 18:56:45 +0200
From:   Jarkko Sakkinen <jarkko@kernel.org>
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     "Yu, Yu-cheng" <yu-cheng.yu@intel.com>, x86@kernel.org,
        "H. Peter Anvin" <hpa@zytor.com>,
        Thomas Gleixner <tglx@linutronix.de>,
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        linux-arch@vger.kernel.org, linux-api@vger.kernel.org,
        Arnd Bergmann <arnd@arndb.de>,
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        Balbir Singh <bsingharora@gmail.com>,
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        Cyrill Gorcunov <gorcunov@gmail.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Eugene Syromiatnikov <esyr@redhat.com>,
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        Haitao Huang <haitao.huang@intel.com>
Subject: Re: [PATCH v22 8/8] x86/vdso: Add ENDBR64 to __vdso_sgx_enter_enclave
Message-ID: <YEudTW1cKAQG10BG@kernel.org>
References: <20210310220519.16811-1-yu-cheng.yu@intel.com>
 <20210310220519.16811-9-yu-cheng.yu@intel.com>
 <YElKjT2v628tidE/@kernel.org>
 <8b8efe44-b79f-ce29-ee28-066f88c93840@intel.com>
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On Thu, Mar 11, 2021 at 09:42:05AM +0100, Peter Zijlstra wrote:
> On Thu, Mar 11, 2021 at 05:36:06AM +0200, Jarkko Sakkinen wrote:
> > Does it do any harm to put it there unconditionally?
> 
> Blows up your text footprint and I$ pressure. These instructions are 4
> bytes each.
> 
> Aside from that, they're a NOP, so only consume front-end resources
> (hopefully) on older CPUs and when IBT is disabled.

OK, understood, thanks for the explanation.

/Jarkko