On Thu, 24 Oct 2019 07:40:39 -0400 Janosch Frank <frankja@xxxxxxxxxxxxx> wrote: > As guest memory is inaccessible and information about the guest's > state is very limited, new ways for instruction emulation have been > introduced. > > With a bounce area for guest GRs and instruction data, guest state > leaks can be limited by the Ultravisor. KVM now has to move > instruction input and output through these areas. > > Signed-off-by: Janosch Frank <frankja@xxxxxxxxxxxxx> > --- > Documentation/virtual/kvm/s390-pv.txt | 47 +++++++++++++++++++++++++++ > 1 file changed, 47 insertions(+) > > diff --git a/Documentation/virtual/kvm/s390-pv.txt b/Documentation/virtual/kvm/s390-pv.txt > index e09f2dc5f164..cb08d78a7922 100644 > --- a/Documentation/virtual/kvm/s390-pv.txt > +++ b/Documentation/virtual/kvm/s390-pv.txt > @@ -48,3 +48,50 @@ interception codes have been introduced. One which tells us that CRs > have changed. And one for PSW bit 13 changes. The CRs and the PSW in > the state description only contain the mask bits and no further info > like the current instruction address. > + > + > +Instruction emulation: > +With the format 4 state description the SIE instruction already s/description/description,/ > +interprets more instructions than it does with format 2. As it is not > +able to interpret all instruction, the SIE and the UV safeguard KVM's s/instruction/instructions/ > +emulation inputs and outputs. > + > +Guest GRs and most of the instruction data, like IO data structures Hm, what 'IO data structures'? > +are filtered. Instruction data is copied to and from the Secure > +Instruction Data Area. Guest GRs are put into / retrieved from the > +Interception-Data block. > + > +The Interception-Data block from the state description's offset 0x380 > +contains GRs 0 - 16. Only GR values needed to emulate an instruction > +will be copied into this area. > + > +The Interception Parameters state description field still contains the > +the bytes of the instruction text but with pre-set register > +values. I.e. each instruction always uses the same instruction text, > +to not leak guest instruction text. > + > +The Secure Instruction Data Area contains instruction storage > +data. Data for diag 500 is exempt from that and has to be moved > +through shared buffers to KVM. I find this paragraph a bit confusing. What does that imply for diag 500 interception? Data is still present in gprs 1-4? (Also, why only diag 500? Because it is the 'reserved for kvm' diagnose call?) > + > +When SIE intercepts an instruction, it will only allow data and > +program interrupts for this instruction to be moved to the guest via > +the two data areas discussed before. Other data is ignored or results > +in validity interceptions. > + > + > +Instruction emulation interceptions: > +There are two types of SIE secure instruction intercepts. The normal > +and the notification type. Normal secure instruction intercepts will > +make the guest pending for instruction completion of the intercepted > +instruction type, i.e. on SIE entry it is attempted to complete > +emulation of the instruction with the data provided by KVM. That might > +be a program exception or instruction completion. > + > +The notification type intercepts inform KVM about guest environment > +changes due to guest instruction interpretation. Such an interception 'interpretation by SIE' ? > +is recognized for the store prefix instruction and provides the new > +lowcore location for mapping change notification arming. Any KVM data > +in the data areas is ignored, program exceptions are not injected and > +execution continues on next SIE entry, as if no intercept had > +happened.
