Messages in this thread | | | From | Geert Uytterhoeven <> | Date | Fri, 12 Jan 2018 11:38:58 +0100 | Subject | Re: [PATCH v2 01/19] Documentation: document array_ptr |
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Hi Dan,
On Fri, Jan 12, 2018 at 1:46 AM, Dan Williams <dan.j.williams@intel.com> wrote: > From: Mark Rutland <mark.rutland@arm.com> > > Document the rationale and usage of the new array_ptr() helper. > > Signed-off-by: Mark Rutland <mark.rutland@arm.com> > Signed-off-by: Will Deacon <will.deacon@arm.com> > Cc: Dan Williams <dan.j.williams@intel.com> > Cc: Jonathan Corbet <corbet@lwn.net> > Cc: Peter Zijlstra <peterz@infradead.org> > Signed-off-by: Dan Williams <dan.j.williams@intel.com>
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 -- geert@linux-m68k.org
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
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