From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:35178) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1dsrjg-0000eT-Na for qemu-devel@nongnu.org; Fri, 15 Sep 2017 10:36:53 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1dsrjd-0007uI-Jt for qemu-devel@nongnu.org; Fri, 15 Sep 2017 10:36:52 -0400 Received: from mx1.redhat.com ([209.132.183.28]:43150) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1dsrjd-0007tD-E5 for qemu-devel@nongnu.org; Fri, 15 Sep 2017 10:36:49 -0400 References: <1490347615-19222-1-git-send-email-thuth@redhat.com> <129fdced-8f83-e408-b37a-26c6ba8bb48f@de.ibm.com> From: Thomas Huth Message-ID: <169bbaaf-3212-ce1d-a0db-6edede5b481d@redhat.com> Date: Fri, 15 Sep 2017 16:36:45 +0200 MIME-Version: 1.0 In-Reply-To: <129fdced-8f83-e408-b37a-26c6ba8bb48f@de.ibm.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH] target/s390x/kvm: Fix problem when running with SELinux under z/VM List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Christian Borntraeger , qemu-devel@nongnu.org Cc: Cornelia Huck On 29.03.2017 16:25, Christian Borntraeger wrote: > On 03/29/2017 04:21 PM, Thomas Huth wrote: >> On 24.03.2017 10:39, Christian Borntraeger wrote: >>> On 03/24/2017 10:26 AM, Thomas Huth wrote: >>>> When running QEMU with KVM under z/VM, the memory for the guest >>>> is allocated via legacy_s390_alloc() since the KVM_CAP_S390_COW >>>> extension is not supported on z/VM. legacy_s390_alloc() then uses >>>> mmap(... PROT_EXEC ...) for the guest memory - but this does not >>>> work when running with SELinux enabled, mmap() fails and QEMU aborts >>>> with the following error message: >>>> >>>> cannot set up guest memory 's390.ram': Permission denied >>>> >>>> Looking at the other allocator function qemu_anon_ram_alloc(), it >>>> seems like PROT_EXEC is normally not needed for allocating the >>>> guest RAM, and indeed, the guest also starts successfully under >>>> z/VM when we remove the PROT_EXEC from the legacy_s390_alloc() >>>> function. So let's get rid of that flag here to be able to run >>>> with SELinux under z/VM, too. >>> >>> Older z/VM versions do not provide the enhanced suppression on protection >>> facility, which would result in guest failures as soon as the kernel >>> starts dirty pages tracking by write protecting the pages via the page >>> table. Some kernel release back (last time I checked) the PROT_EXEC was >>> necessary to prevent the dirty pages tracking from taking place. So this >>> patch would break KVM in that case. >>> >>> Newer z/VMs (e.g. 6.3) do provide ESOP. SO the question is, >>> why is KVM_CAP_S390_COW not set? >> >> I now had another look at this, and seems like the ESOP bit is indeed >> not set in S390_lowcore.machine_flags here. According to /proc/sysinfo, >> z/VM is version 6.1.0 here, so I guess that's just too old for ESOP? > > Yes, this was introduced with z/VM 6.3 FWIW, the last version without ESOP, z/VM 6.2, is now end of life, according to: http://www.vm.ibm.com/techinfo/lpmigr/vmleos.html ... so I guess we could remove the legacy_s390_alloc() function now? Thomas