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?
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