On 7/20/2022 8:29 PM, Chao Peng wrote: > On Thu, Jul 14, 2022 at 01:03:46AM +0000, Sean Christopherson wrote: > ... >> >> Option D). track shared regions in an Xarray, update kvm_arch_memory_slot.lpage_info >> on insertion/removal to (dis)allow hugepages as needed. >> >> + efficient on KVM page fault (no new lookups) >> + zero memory overhead (assuming KVM has to eat the cost of the Xarray anyways) >> + straightforward to implement >> + can (and should) be merged as part of the UPM series >> >> I believe xa_for_each_range() can be used to see if a given 2mb/1gb range is >> completely covered (fully shared) or not covered at all (fully private), but I'm >> not 100% certain that xa_for_each_range() works the way I think it does. > > Hi Sean, > > Below is the implementation to support 2M as you mentioned as option D. > It's based on UPM v7 xarray code: https://lkml.org/lkml/2022/7/6/259 > > Everything sounds good, the only trick bit is inc/dec disallow_lpage. If > we still treat it as a count, it will be a challenge to make the inc/dec > balanced. So in this patch I stole a bit for the purpose, looks ugly. > > Any feedback is welcome. > > Thanks, > Chao > > ----------------------------------------------------------------------- > From: Chao Peng <chao.p.peng@xxxxxxxxxxxxxxx> > Date: Wed, 20 Jul 2022 11:37:18 +0800 > Subject: [PATCH] KVM: Add large page support for private memory > > Update lpage_info when handling KVM_MEMORY_ENCRYPT_{UN,}REG_REGION. > > Reserve a bit in disallow_lpage to indicate a large page has > private/share pages mixed. > > Signed-off-by: Chao Peng <chao.p.peng@xxxxxxxxxxxxxxx> > --- > +static void update_mem_lpage_info(struct kvm *kvm, > + struct kvm_memory_slot *slot, > + unsigned int attr, > + gfn_t start, gfn_t end) > +{ > + unsigned long lpage_start, lpage_end; > + unsigned long gfn, pages, mask; > + int level; > + > + for (level = PG_LEVEL_2M; level <= KVM_MAX_HUGEPAGE_LEVEL; level++) { > + pages = KVM_PAGES_PER_HPAGE(level); > + mask = ~(pages - 1); > + lpage_start = start & mask; > + lpage_end = end & mask; > + > + /* > + * We only need to scan the head and tail page, for middle pages > + * we know they are not mixed. > + */ > + update_mixed(lpage_info_slot(lpage_start, slot, level), > + mem_attr_is_mixed(kvm, attr, lpage_start, > + lpage_start + pages)); > + > + if (lpage_start == lpage_end) > + return; > + > + for (gfn = lpage_start + pages; gfn < lpage_end; gfn += pages) { > + update_mixed(lpage_info_slot(gfn, slot, level), false); > + } Boundary check missing here for the case when gfn reaches lpage_end. if (gfn == lpage_end) return; > + > + update_mixed(lpage_info_slot(lpage_end, slot, level), > + mem_attr_is_mixed(kvm, attr, lpage_end, > + lpage_end + pages)); > + } > +} Regards Nikunj
