From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from mail.kernel.org ([198.145.29.99]) by Galois.linutronix.de with esmtps (TLS1.2:DHE_RSA_AES_256_CBC_SHA256:256) (Exim 4.80) (envelope-from ) id 1fGRRe-0007UC-Kk for speck@linutronix.de; Wed, 09 May 2018 17:55:59 +0200 Date: Wed, 9 May 2018 17:55:38 +0200 From: Greg KH Subject: [MODERATED] Re: [PATCH 5/5] SSB extra v2 5 Message-ID: <20180509155538.GA28243@kroah.com> References: =?utf-8?q?=3C3c3bda?= =?utf-8?q?6cd68a91d9e79ef1da60d481180d544d20=2E1525734796=2Egit=2Edave=2E?= =?utf-8?q?hansen=40intel=2Ecom=3E?= <20180508003632.GH4050@tassilo.jf.intel.com> <1ae07e8f-636f-0cbd-399c-e5d538dc93ea@linux.intel.com> MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit To: speck@linutronix.de List-ID: On Wed, May 09, 2018 at 08:43:30AM -0700, speck for Dave Hansen wrote: > On 05/09/2018 08:36 AM, speck for Thomas Gleixner wrote: > >> For now, it *is* generic, though. It's whether the mitigation function > >> gets injected into the call path or not. > >> > >> Once we have multiple things we have to mitigate for at entry/exit, we > >> may need to add some other flags to the bpf_prog that say exactly what > >> mitigations we need, like a "bfp_prog->does_memory_write" that > >> explicitly tells us if we need the SSB mitigation. > > Now looking at the overhead of this SSB hardware mitigation stuff I really > > wonder what's the state on investigating software mitigations for BPF. > > > > The magic PDF talks about that, but has anyone looked at that? > > I don't know of anyone that has. I'm fairly sure no one at Intel has > looked in detail, at least in the post-Spectre timeframe. > > Frankly, I think it's mostly a waste of time to do it without having the > BPF folks deeply involved from day one. They were not fans of the way > we (Intel) did Spectre V1 mitigations and I don't expect this to be any > different. > > They were deeply opposed to LFENCE getting used, for instance. Great, why can't we drag them into this then? We obviously need their help, as anything we come up with is going to just be made fun of by them :) thanks, greg k-h