From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stas Sergeev Subject: Re: Warning about kernel 4.2 performance (revised) Date: Mon, 5 Oct 2015 14:20:41 +0300 Message-ID: <56125D09.4000108@list.ru> References: <20151003085631.02f5b16dfebc7020bf3a1edb@spheresystems.co.uk> <20151004081607.881df23245f969d66eba63b0@spheresystems.co.uk> <5610E4E5.2090802@earthlink.net> <20151004113203.b07e3f6ac66bcba747d75903@spheresystems.co.uk> <56116148.9050608@earthlink.net> <561163AA.6040706@list.ru> <20151005104705.7b2df50cac63a976412ecc22@spheresystems.co.uk> Mime-Version: 1.0 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=list.ru; s=mail; h=Content-Transfer-Encoding:Content-Type:In-Reply-To:MIME-Version:Date:Message-ID:From:Cc:References:To:Subject; bh=97fgTcAnESx+BDNLJCwoQ1lP/vnPe9BaAfCaTsFNtE0=; b=M8BJ7I66EwNI2dfSQJjzKYPnqAZcNsgWrCycN+DoBgNhP1RPYt5yIzX8+iNTVptJH292S6qkYBTcexpS/+sstLE3KdMf7Uncky3wki6aDG4V9e6+BwYcn2m39mQh1YdIEx0x+mfPtMmY+KYhy46CO+gA+WliPRACOG6WVS5+NqY=; In-Reply-To: <20151005104705.7b2df50cac63a976412ecc22@spheresystems.co.uk> Sender: linux-msdos-owner@vger.kernel.org List-ID: Content-Type: text/plain; charset="utf-8" To: Andrew Bird Cc: Felix Miata , linux-msdos@vger.kernel.org 05.10.2015 12:47, Andrew Bird =D0=BF=D0=B8=D1=88=D0=B5=D1=82: > Mmm, that thread is full of the same old rhetoric (i.e. it must be a = risk as no one can be bothered/has time to check it and users > must be prevented from hurting themselves even if they've already jum= ped through hoops to enable mm.vm_addr=3D0, which is a known security > risk, so that dosemu can function with cpuemu=3Doff). I do fail to se= e why the default can't have the vm86() syscall compiled in, but > disabled by default at run time. As Felix pointed, this is exactly what happens. But really, having never delivering dosemu, keeping vm86 ON is pretty useless for them, so I won't bet on this to stay forever. But now as it can be disabled at run-time - the chances are big they'll no longer re-visit this subject and leave it as is. Note that AFAIK dosemu can't use vm86 on fedora even if enabled both compile-time and run-time, because selinux then prevents mapping zero page even if you enabled it in mmap_min_addr (but I may be wrong, someone needs to double-check also this). The security threat may come from the fact that you need to disable selinux. > Regarding RHEL kernels, I've used CentOS 3, 4, 5 and 6 successfully w= ith Dosemu cpuemu=3Doff, so CONFIG_VM86=3Dy was set on those. Have you disabled selinux? -- To unsubscribe from this list: send the line "unsubscribe linux-msdos" = in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html