From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from s3.sipsolutions.net ([2a01:4f8:191:4433::2] helo=sipsolutions.net) by bombadil.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1j2AO3-0007Uv-M5 for linux-um@lists.infradead.org; Thu, 13 Feb 2020 09:02:20 +0000 Message-ID: <817580a4bcfbd3ef3ce31dfc5876bb99c3fca832.camel@sipsolutions.net> Subject: Re: [RFC PATCH v2] UML: add support for KASAN under x86_64 From: Johannes Berg Date: Thu, 13 Feb 2020 10:02:05 +0100 In-Reply-To: (sfid-20200213_094451_311672_27C02820) References: <20200210225806.249297-1-trishalfonso@google.com> <13b0ea0caff576e7944e4f9b91560bf46ac9caf0.camel@sipsolutions.net> (sfid-20200213_094451_311672_27C02820) MIME-Version: 1.0 List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-um" Errors-To: linux-um-bounces+geert=linux-m68k.org@lists.infradead.org To: Dmitry Vyukov Cc: Patricia Alfonso , Richard Weinberger , Jeff Dike , Brendan Higgins , LKML , kasan-dev , linux-um@lists.infradead.org, David Gow , Andrey Ryabinin , anton.ivanov@cambridgegreys.com On Thu, 2020-02-13 at 09:44 +0100, Dmitry Vyukov wrote: > > Right, but again like below - that's just mapped, not actually used. But > > as far as I can tell, once you actually start running and potentially > > use all of your mem=1024 (MB), you'll actually also use another 128MB on > > the KASAN shadow, right? > > > > Unlike, say, a real x86_64 machine where if you just have 1024 MB > > physical memory, the KASAN shadow will have to fit into that as well. > > Depends on what you mean by "real" :) :) > Real user-space ASAN will also reserve 1/8th of 47-bit VA on start > (16TB). Ah, but I was thinking of actual memory *used*, not just VA. And of KASAN, not user-space, but yeah, good point. > This implementation seems to be much closer to user-space ASAN > rather than to x86_64 KASAN (in particular it seems to be mostly > portable across archs and is not really x86-specific, which is good). Indeed. > I think it's reasonable and good, but the implementation difference > with other kernel arches may be worth noting somewhere in comments. Right, I guess that's the broader point. I was thinking mostly of the memory consumption: if you run with UML KASAN, your UML virtual machine will use around 12.5% more memory than before, unlike if you say have a KVM virtual machine - whatever you reserve outside will be what it can use inside, regardless of KASAN being enabled or not. This is totally fine, I just thought it should be documented somewhere, perhaps in the Kconfig option, though I guess there isn't a UML specific one for this... Not sure where then. johannes _______________________________________________ linux-um mailing list linux-um@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-um