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    SubjectRe: [PATCH 26/26] x86, pkeys: Documentation
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    On 10/03/2015 12:27 AM, Ingo Molnar wrote:
    > - Along similar considerations, also add a sys_pkey_query() system call to query
    > the mapping of a specific pkey. (returns -EBADF or so if the key is not mapped
    > at the moment.) This too could be vDSO accelerated in the future.
    >
    > I.e. something like:
    >
    > unsigned long sys_pkey_alloc (unsigned long flags, unsigned long init_val)
    > unsigned long sys_pkey_set (int pkey, unsigned long new_val)
    > unsigned long sys_pkey_get (int pkey)
    > unsigned long sys_pkey_free (int pkey)

    The pkey_set() operation is going to get a wee bit interesting with signals.

    pkey_set() will modify the _current_ context's PKRU which includes the
    register itself and the kernel XSAVE buffer (if active). But, since the
    PKRU state is saved/restored with the XSAVE state, we will blow away any
    state set during the signal.

    I _think_ the right move here is to either keep a 'shadow' version of
    PKRU inside the kernel (for each thread) and always update the task's
    XSAVE PKRU state when returning from a signal handler. Or, _copy_ the
    signal's PKRU state in to the main process's PKRU state when returning
    from a signal.


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