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    SubjectRe: [PATCH 02/19] x86, fpu: wrap get_xsave_addr() to make it safer
    On Fri, 8 May 2015, Dave Hansen wrote:
    > The MPX code appears to be saving off the FPU in an unsafe
    > way. It does not disable preemption or ensure that the
    > FPU state has been allocated.
    >
    > This patch introduces a new helper which will do both of
    > those things internally.

    This changelog does not really match the implementation. Unless I'm
    missing something I can't find anything preemption related.

    > +
    > +/*
    > + * This wraps up the common operations that need to occur when retrieving
    > + * data from xsave state. It first ensures that the current task was
    > + * using the FPU and retrieves the data in to a buffer. It then calculates
    > + * the offset of the requested field in the buffer.
    > + *
    > + * This function is safe to call whether the FPU is in use or not.
    > + *
    > + * Note that this only works on the current task.
    > + *
    > + * Inputs:
    > + * @xsave_field: state which is defined in xsave.h (e.g. XSTATE_FP,
    > + * XSTATE_SSE, etc...)
    > + * Output:
    > + * address of the state in the xsave area.

    or NULL in case of .....

    > + */
    > +void *get_xsave_field(int xsave_field)
    > +{
    > + union thread_xstate *xstate;
    > +
    > + if (!tsk_used_math(current))
    > + return NULL;
    > + /*
    > + * unlazy_fpu() is poorly named and will actually
    > + * save the xstate off in to the memory buffer.
    > + */
    > + unlazy_fpu(current);
    > + xstate = current->thread.fpu.state;
    > +
    > + return get_xsave_addr(&xstate->xsave, xsave_field);
    > +}

    Thanks,

    tglx


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