Re: [PATCH] x86_64, asm: Work around AMD SYSRET SS descriptor attribute issue

Linus Torvalds
2015-04-27T18:47:32Z

On Mon, Apr 27, 2015 at 11:38 AM, Borislav Petkov <bp@alien8.de> wrote:
>
> So our current NOP-infrastructure does ASM_NOP_MAX NOPs of 8 bytes so
> without more invasive changes, our longest NOPs are 8 byte long and then
> we have to repeat.

Btw (and I'm too lazy to check) do we take alignment into account?

Because if you have to split, and use multiple nops, it is *probably*
a good idea to try to avoid 16-byte boundaries, since that's can be
the I$ fetch granularity from L1 (although I guess 32B is getting more
common).

So the exact split might depend on the alignment of the nop replacement..

> You can recognize the p6_nops being the same as in-the-manual-suggested
> F16h ones.

Can we perhaps get rid of the distinction entirely, and just use one
set of 64-bit nops for both Intel/AMD?

Linus