| From | (Eric W. Biederman) | Date | Thu, 11 Jan 2018 20:42:41 -0600 | Subject | Re: [PATCH v2 06/19] asm-generic/barrier: mask speculative execution flows |
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Dan Williams <dan.j.williams@intel.com> writes:
> diff --git a/include/linux/nospec.h b/include/linux/nospec.h > new file mode 100644 > index 000000000000..5c66fc30f919 > --- /dev/null > +++ b/include/linux/nospec.h > @@ -0,0 +1,71 @@ > +// SPDX-License-Identifier: GPL-2.0 > +// Copyright(c) 2018 Intel Corporation. All rights reserved. > + > +#ifndef __NOSPEC_H__ > +#define __NOSPEC_H__ > + > +#include <linux/jump_label.h> > +#include <asm/barrier.h> > + > +#ifndef array_ptr_mask > +#define array_ptr_mask(idx, sz) \ > +({ \ > + unsigned long mask; \ > + unsigned long _i = (idx); \ > + unsigned long _s = (sz); \ > + \ > + mask = ~(long)(_i | (_s - 1 - _i)) >> (BITS_PER_LONG - 1); \ > + mask; \ > +}) > +#endif
This could really use a comment that explains it generates 0 for out of bound accesses and -1L aka 0xffffffffffffffff for all other accesses.
The code is clever enough which values it generates is not obvious.
Eric
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