KVM: Simply gfn_to_page()

Mapping a guest page to a host page is a common operation.  Currently,
one has first to find the memory slot where the page belongs (gfn_to_memslot),
then locate the page itself (gfn_to_page()).

This is clumsy, and also won't work well with memory aliases.  So simplify
gfn_to_page() not to require memory slot translation first, and instead do it
internally.

Signed-off-by: Avi Kivity <avi@qumranet.com>
diff --git a/drivers/kvm/kvm.h b/drivers/kvm/kvm.h
index 59357be..d19985a 100644
--- a/drivers/kvm/kvm.h
+++ b/drivers/kvm/kvm.h
@@ -443,11 +443,7 @@
 
 extern hpa_t bad_page_address;
 
-static inline struct page *gfn_to_page(struct kvm_memory_slot *slot, gfn_t gfn)
-{
-	return slot->phys_mem[gfn - slot->base_gfn];
-}
-
+struct page *gfn_to_page(struct kvm *kvm, gfn_t gfn);
 struct kvm_memory_slot *gfn_to_memslot(struct kvm *kvm, gfn_t gfn);
 void mark_page_dirty(struct kvm *kvm, gfn_t gfn);
 
@@ -523,12 +519,6 @@
 	return vcpu->mmu.page_fault(vcpu, gva, error_code);
 }
 
-static inline struct page *_gfn_to_page(struct kvm *kvm, gfn_t gfn)
-{
-	struct kvm_memory_slot *slot = gfn_to_memslot(kvm, gfn);
-	return (slot) ? slot->phys_mem[gfn - slot->base_gfn] : NULL;
-}
-
 static inline int is_long_mode(struct kvm_vcpu *vcpu)
 {
 #ifdef CONFIG_X86_64