On Mon, Jul 25, 2022 at 07:16:24PM +0530, Nikunj A. Dadhania wrote: > 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; In this case, it's actually the tail page that I want to scan for with below code. It's also possible I misunderstand something here. Chao > > > + > > + update_mixed(lpage_info_slot(lpage_end, slot, level), > > + mem_attr_is_mixed(kvm, attr, lpage_end, > > + lpage_end + pages)); > > + } > > +} > > Regards > Nikunj
