On 14.02.2018 16:01, Janosch Frank wrote: > On 14.02.2018 15:30, David Hildenbrand wrote: >> On 09.02.2018 10:34, Janosch Frank wrote: >>> Since the z10 s390 does support 1M pages, but whereas hugetlbfs >>> support was added quite fast, KVM always used standard 4k pages for >>> guest backings. >>> >>> This patchset adds full support for 1M huge page backings for s390 >>> KVM guests. I.e. we also support VSIE (nested vms) for these guests >>> and are therefore able to run all combinations of backings for all >>> layers of guests. >>> >>> When running a VSIE guest in a huge page backed guest, we need to >>> split some huge pages to be able to set granular protection. This way >>> we avoid a prot/unprot cycle if prefixes and VSIE pages containing >>> level 3 gmap DAT tables share the same segment, as the prefix has to >>> be accessible at all times and the VSIE page has to be write >>> protected. >>> >>> Branch: >>> git://git.kernel.org/pub/scm/linux/kernel/git/kvms390/linux.git hlp_vsie >>> https://git.kernel.org/pub/scm/linux/kernel/git/kvms390/linux.git/log/?h=hlp_vsie >>> >> >> A general proposal: We will have split PMDs with fake PGSTE. This is >> nasty but needed. I think we should hinder virtualization from making >> use of these. Just like we already do for vSIE. >> >> Should we make the KVM_CAP_S390_HPAGE a configuration option? >> >> Without it being set, don't allow mapping huge pages into the GMAP. >> Everything as usual. >> >> With it being set (by user space when it thinks we need huge pages), >> allow mapping huge pages into the GMAP AND >> - Explicitly disable CMMA. Right now we trust on user space to do the >> right thing. ecb2 &= ~ECB2_CMMA >> - Disable PFMFI -> ecb2 &= ~ECB2_PFMFI >> - Disable SKF by setting scb->ictl |= ICTL_ISKE | ICTL_SSKE | ICTL_RRBE >> >> So user space has to explicitly indicate and allow huge pages. This will >> result in all instructions that touch the PGSTE getting intercepted, so >> we can properly work on the huge PMDs instead. > > My only concern here is: > Can this coexist with the cpumodels in a coordinated way? > We already have to fake away the CMMA facility in user space. So that shouldn't be a problem. The other instructions - PFMF - ISKE, SSKE ... Will simply always be interpreted. Should not affect the CPU model. -- Thanks, David / dhildenb
