On 7/26/2022 8:02 PM, Chao Peng wrote: > 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. What if you do not have the tail lpage? For example: memslot base_gfn = 0x1000 and npages is 0x800, so memslot range is 0x1000 to 0x17ff. Assume a case when this function is called with start = 1000 and end = 1800. For 2M, page mask is 0x1ff. start and end both are 2M aligned. First update_mixed takes care of 0x1000-0x1200 Loop update_mixed: goes over from 0x1200 - 0x1800, there are no pages left for last update_mixed to process. > > 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)); lpage_info_slot some times causes a crash, as I noticed that lpage_info_slot() returns out-of-bound index. Regards Nikunj
