Date: Fri, 05 Jan 2018 09:15:16 +0100 From: =?utf-8?Q?Dag-Erling_Sm=C3=B8rgrav?= <des@des.no> To: Eric McCorkle <eric@metricspace.net> Cc: "freebsd-security\@freebsd.org" <freebsd-security@freebsd.org> Subject: Re: A more general possible meltdown/spectre countermeasure Message-ID: <86efn4u3fv.fsf@desk.des.no> In-Reply-To: <c98b7ac3-26f0-81ee-2769-432697f876e5@metricspace.net> (Eric McCorkle's message of "Thu, 4 Jan 2018 23:05:40 -0500") References: <c98b7ac3-26f0-81ee-2769-432697f876e5@metricspace.net>
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Eric McCorkle <eric@metricspace.net> writes: > The obvious downside is that you take a performance hit storing things > in non-cacheable locations, especially if you plan on doing heavy > computation in that memory (say, encryption/decryption). However, this > is almost certainly going to be less than the projected 30-50% > performance hit from other mitigations. Where did you get those numbers? Because the worst documented case for KPTI is ~20% for I/O-intensive workloads, and PCID is likely to bring this down to single digits if used correctly. The KAISER paper claims a slowdown of < 1%, but that may have been the result of undisclosed features of the specific CPU they tested on. DES --=20 Dag-Erling Sm=C3=B8rgrav - des@des.no
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