On Mon, Apr 27, 2015 at 11:47:30AM -0700, Linus Torvalds wrote: > On Mon, Apr 27, 2015 at 11:38 AM, Borislav Petkov <b...@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).
Yeah, on F16h you have 32B fetch but the paths later in the machine gets narrower, so to speak. > So the exact split might depend on the alignment of the nop replacement.. Yeah, no. Our add_nops() is trivial: /* Use this to add nops to a buffer, then text_poke the whole buffer. */ static void __init_or_module add_nops(void *insns, unsigned int len) { while (len > 0) { unsigned int noplen = len; if (noplen > ASM_NOP_MAX) noplen = ASM_NOP_MAX; memcpy(insns, ideal_nops[noplen], noplen); insns += noplen; len -= noplen; } } > Can we perhaps get rid of the distinction entirely, and just use one > set of 64-bit nops for both Intel/AMD? I *think* hpa would have an opinion here. I'm judging by looking at comments like this one in the code: /* * Due to a decoder implementation quirk, some * specific Intel CPUs actually perform better with * the "k8_nops" than with the SDM-recommended NOPs. */ which is a fun one in itself. :-) -- Regards/Gruss, Boris. ECO tip #101: Trim your mails when you reply. -- -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/