Hi Dan,
On Fri, Jan 12, 2018 at 1:46 AM, Dan Williams <[email protected]> wrote:
> From: Mark Rutland <[email protected]>
>
> Document the rationale and usage of the new array_ptr() helper.
>
> Signed-off-by: Mark Rutland <[email protected]>
> Signed-off-by: Will Deacon <[email protected]>
> Cc: Dan Williams <[email protected]>
> Cc: Jonathan Corbet <[email protected]>
> Cc: Peter Zijlstra <[email protected]>
> Signed-off-by: Dan Williams <[email protected]>
Thanks for the update!
> --- /dev/null
> +++ b/Documentation/speculation.txt
> @@ -0,0 +1,142 @@
> +This document explains potential effects of speculation, and how undesirable
> +effects can be mitigated portably using common APIs.
> +
> +===========
> +Speculation
> +===========
> +
> +To improve performance and minimize average latencies, many contemporary CPUs
> +employ speculative execution techniques such as branch prediction, performing
> +work which may be discarded at a later stage.
> +
> +Typically speculative execution cannot be observed from architectural state,
> +such as the contents of registers. However, in some cases it is possible to
> +observe its impact on microarchitectural state, such as the presence or
> +absence of data in caches. Such state may form side-channels which can be
> +observed to extract secret information.
> +
> +For example, in the presence of branch prediction, it is possible for bounds
> +checks to be ignored by code which is speculatively executed. Consider the
> +following code:
> +
> + int load_array(int *array, unsigned int idx) {
One more opening curly brace to move to the next line.
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- [email protected]
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
