Quoting Janosch Frank (2023-03-28 16:13:04) > On 3/27/23 10:21, Nico Boehr wrote: > > This is to prepare for running guests without MSO/MSL, which is > > currently not possible. > > > > We already have code in sie64a to setup a guest primary ASCE before > > entering SIE, so we can in theory switch to the page tables which > > translate gpa to hpa. > > > > But the host is running in primary space mode already, so changing the > > primary ASCE before entering SIE will also affect the host's code and > > data. > > > > To make this switch useful, the host should run in a different address > > space mode. Hence, set up and change to home address space mode before > > installing the guest ASCE. > > > > The home space ASCE is just copied over from the primary space ASCE, so > > no functional change is intended, also for tests that want to use > > MSO/MSL. If a test intends to use a different primary space ASCE, it can > > now just set the guest.asce in the save_area. > > > [...] > > + /* set up home address space to match primary space */ > > + old_cr13 = stctg(13); > > + lctlg(13, stctg(1)); > > + > > + /* switch to home space so guest tables can be different from host */ > > + psw_mask_set_bits(PSW_MASK_HOME); > > + > > + /* also handle all interruptions in home space while in SIE */ > > + lowcore.pgm_new_psw.mask |= PSW_MASK_DAT_HOME; > > > + lowcore.ext_new_psw.mask |= PSW_MASK_DAT_HOME; > > + lowcore.io_new_psw.mask |= PSW_MASK_DAT_HOME; > We didn't enable DAT in these two cases as far as I can see so this is > superfluous or we should change the mmu code. Also it's missing the svc > and machine check. Right. Is there a particular reason why we only run DAT on for PGM ints? > The whole bit manipulation thing looks a bit crude. It might make more > sense to drop into real mode for a few instructions and have a dedicated > storage location for an extended PSW mask and an interrupt ASCE as part > of the interrupt call code instead. > > Opinions? Maybe I don't get it, but I personally don't quite see the advantage. It seems to me this would make things much more complicated just to avoid a few simple bitops. It maybe also depends on how many new_psws we have to touch. If it's really just the PGM, the current solution seems simple enough. But if others also prefer Janosch's suggestion, I am happy to implement it.
