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Date:   Sun, 17 May 2020 23:18:36 -0700
From:   Christoph Hellwig <hch@infradead.org>
To:     Sasha Levin <sashal@kernel.org>
Cc:     linux-kernel@vger.kernel.org, tglx@linutronix.de, bp@alien8.de,
        luto@kernel.org, hpa@zytor.com, dave.hansen@intel.com,
        tony.luck@intel.com, ak@linux.intel.com, ravi.v.shankar@intel.com,
        chang.seok.bae@intel.com
Subject: Re: [PATCH v12 00/18] Enable FSGSBASE instructions
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References: <20200511045311.4785-1-sashal@kernel.org>
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On Mon, May 11, 2020 at 12:52:53AM -0400, Sasha Levin wrote:
> Benefits:
> Currently a user process that wishes to read or write the FS/GS base must
> make a system call. But recent X86 processors have added new instructions
> for use in 64-bit mode that allow direct access to the FS and GS segment
> base addresses.  The operating system controls whether applications can
> use these instructions with a %cr4 control bit.
> 
> In addition to benefits to applications, performance improvements to the
> OS context switch code are possible by making use of these instructions. A
> third party reported out promising performance numbers out of their
> initial benchmarking of the previous version of this patch series [9].

The [9] reference can't be resolved anywhere in this mail.