On Fri, Jan 11, 2019 at 02:58:26PM +0200, Jarkko Sakkinen wrote: > On Wed, Jan 09, 2019 at 08:31:37AM -0800, Sean Christopherson wrote: > > On Tue, Jan 08, 2019 at 02:54:11PM -0800, Andy Lutomirski wrote: > > > On Tue, Jan 8, 2019 at 2:09 PM Sean Christopherson > > > <sean.j.christopherson@xxxxxxxxx> wrote: > > > > > > > > Cleaner in the sense that it's faster to get basic support up and running > > > > since there are fewer touchpoints, but there are long term ramifications > > > > to cramming EPC management in KVM. > > > > > > > > And at this point I'm not stating any absolutes, e.g. how EPC will be > > > > handled by KVM. What I'm pushing for is to not eliminate the possibility > > > > of having the SGX subsystem own all EPC management, e.g. don't tie > > > > /dev/sgx to a single enclave. > > > > > > I haven't gone and re-read all the relevant SDM bits, so I'll just > > > ask: what, if anything, are the actual semantics of mapping "raw EPC" > > > like this? You can't actually do anything with the mapping from user > > > mode unless you actually get an enclave created and initialized in it > > > and have it mapped at the correct linear address, right? I still > > > think you have the right idea, but it is a bit unusual. > > > > Correct, the EPC is inaccessible until a range is "mapped" with ECREATE. > > But I'd argue that it's not unusual, just different. And really it's not > > all that different than userspace mmap'ing /dev/sgx/enclave prior to > > ioctl(ENCLAVE_CREATE). In that case, userspace can still (attempt to) > > access the "raw" EPC, i.e. generate a #PF, the kernel/driver just happens > > to consider any faulting EPC address without an associated enclave as > > illegal, e.g. signals SIGBUS. > > > > The /dev/sgx/epc case simply has different semantics for moving pages in > > and out of the EPC, i.e. different fault and eviction semantics. Yes, > > this allows the guest kernel to directly access the "raw" EPC, but that's > > conceptually in line with hardware where priveleged software can directly > > "access" the EPC (or rather, the abort page for all intents and purposes). > > I.e. it's an argument for requiring certain privileges to open /dev/sgx/epc, > > but IMO it's not unusual. > > > > Maybe /dev/sgx/epc is a poor name and is causing confusion, e.g. > > /dev/sgx/virtualmachine might be more appropriate. > > What do you mean by saying "requiring certain privileges"? Are you > saying that "raw EPC" (lets say /dev/vmsgx, which probably the name I > will use for the device *if* it is required) device would require > differet privileged than /dev/sgx? I'd say that it would be a good goal to be able to create a VM as a normal user and use SGX. /Jarkko
