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
