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? Thomas
