KVM: MMU: fix comment in kvm_mmu_zap_collapsible_spte

Soft mmu uses direct shadow page to fill guest large mapping with small
pages if huge mapping is disallowed on host. So zapping direct shadow
page works well both for soft mmu and hard mmu, it's just less widely
applicable.

Fix the comment to reflect this.
Signed-off-by: NXiao Guangrong <guangrong.xiao@linux.intel.com>
Message-Id: <552C91BA.1010703@linux.intel.com>
[Fix comment wording further. - Paolo]
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/mmu.c

@@ -4481,9 +4481,11 @@ static bool kvm_mmu_zap_collapsible_spte(struct kvm *kvm,
 		pfn = spte_to_pfn(*sptep);
 
 		/*
-		 * Only EPT supported for now; otherwise, one would need to
-		 * find out efficiently whether the guest page tables are
-		 * also using huge pages.
+		 * We cannot do huge page mapping for indirect shadow pages,
+		 * which are found on the last rmap (level = 1) when not using
+		 * tdp; such shadow pages are synced with the page table in
+		 * the guest, and the guest page table is using 4K page size
+		 * mapping if the indirect sp has level = 1.
 		 */
 		if (sp->role.direct &&
 			!kvm_is_reserved_pfn(pfn) &&