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    SubjectRe: [PATCH RFC 3/4] x86/pti: don't mark the user PGD with _PAGE_NX.
    On Mon, 8 Jan 2018, Willy Tarreau wrote:
    > Since we're going to keep running on the same PGD when returning to
    > userspace for certain performance-critical tasks, we'll need the user
    > pages to be executable. So this code disables the extra protection
    > that was added consisting in marking user pages _PAGE_NX so that this
    > pgd remains usable for userspace.
    >
    > Note: it isn't necessarily the best approach, but one way or another
    > if we want to be able to return to userspace from the kernel,
    > we'll have to have this executable anyway. Another approach
    > might consist in using another pgd for userland+kernel but
    > the current core really looks like an extra careful measure
    > to catch early bugs if any.

    I surely want to keep that as a safety measure. The entry code is simple to
    get wrong and running with the wrong pagetables by a silly mistake and
    thereby undoing the protection is surely not what we want.

    Need to find a free time slot to think about that.

    Thanks,

    tglx

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