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    SubjectRe: [PATCH 00/15] x86: Enable FSGSBASE instructions
    On Mon, Mar 19, 2018 at 5:49 PM, Chang S. Bae <chang.seok.bae@intel.com> wrote:
    > FSGSBASE is 64-bit instruction set to allow read/write
    > FS/GS base from any privilege. As introduced from
    > Ivybridge, enabling effort has been revolving quite long
    > [2,3,4] for various reasons. After extended discussions [1],
    > this patchset is proposed to introduce new ABIs of
    > customizing FS/GS base (separate from its selector).
    >
    > FSGSBASE-enabled VM can be located on hosts with
    > either HW virtualization or SW emulation. KVM advertises
    > FSGSBASE when physical CPU has and emulation is
    > supported in QEMU/TCG [5]. In a pool of mixed systems, VMM
    > may disable FSGSBASE for seamless VM migrations [6].
    >
    > A couple of major benefits are expected. Kernel will have
    > performance improvement in context switch by skipping MSR
    > write for GS base. User-level programs (such as JAVA-based)
    > benefit from avoiding system calls to edit FS/GS base.

    Can you describe what changed since the last submission? It looks
    like a lot has changed and this series is much more complicated and
    much more fragile than it used to be. Why?

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