KVM: remove kvm_clear_guest_page

kvm_clear_guest_page is not used anymore after "KVM: X86: Don't track dirty
for KVM_SET_[TSS_ADDR|IDENTITY_MAP_ADDR]", except from kvm_clear_guest.
We can just inline it in its sole user.
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

include/linux/kvm_host.h

@@ -792,7 +792,6 @@ int kvm_gfn_to_hva_cache_init(struct kvm *kvm, struct gfn_to_hva_cache *ghc,
 			offset_in_page(__gpa), v);			\
 })
 
-int kvm_clear_guest_page(struct kvm *kvm, gfn_t gfn, int offset, int len);
 int kvm_clear_guest(struct kvm *kvm, gpa_t gpa, unsigned long len);
 struct kvm_memory_slot *gfn_to_memslot(struct kvm *kvm, gfn_t gfn);
 bool kvm_is_visible_gfn(struct kvm *kvm, gfn_t gfn);

virt/kvm/kvm_main.c

@@ -2616,23 +2616,16 @@ int kvm_read_guest_cached(struct kvm *kvm, struct gfn_to_hva_cache *ghc,
 }
 EXPORT_SYMBOL_GPL(kvm_read_guest_cached);
 
-int kvm_clear_guest_page(struct kvm *kvm, gfn_t gfn, int offset, int len)
-{
-	const void *zero_page = (const void *) __va(page_to_phys(ZERO_PAGE(0)));
-
-	return kvm_write_guest_page(kvm, gfn, zero_page, offset, len);
-}
-EXPORT_SYMBOL_GPL(kvm_clear_guest_page);
-
 int kvm_clear_guest(struct kvm *kvm, gpa_t gpa, unsigned long len)
 {
+	const void *zero_page = (const void *) __va(page_to_phys(ZERO_PAGE(0)));
 	gfn_t gfn = gpa >> PAGE_SHIFT;
 	int seg;
 	int offset = offset_in_page(gpa);
 	int ret;
 
 	while ((seg = next_segment(len, offset)) != 0) {
-		ret = kvm_clear_guest_page(kvm, gfn, offset, seg);
+		ret = kvm_write_guest_page(kvm, gfn, zero_page, offset, len);
 		if (ret < 0)
 			return ret;
 		offset = 0;