KVM: Take a 'struct page', not a pfn in kvm_is_zone_device_page()

Operate on a 'struct page' instead of a pfn when checking if a page is a
ZONE_DEVICE page, and rename the helper accordingly.  Generally speaking,
KVM doesn't actually care about ZONE_DEVICE memory, i.e. shouldn't do
anything special for ZONE_DEVICE memory.  Rather, KVM wants to treat
ZONE_DEVICE memory like regular memory, and the need to identify
ZONE_DEVICE memory only arises as an exception to PG_reserved pages. In
other words, KVM should only ever check for ZONE_DEVICE memory after KVM
has already verified that there is a struct page associated with the pfn.

No functional change intended.
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20220429010416.2788472-9-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/mmu/mmu.c

@@ -2788,15 +2788,16 @@ static void direct_pte_prefetch(struct kvm_vcpu *vcpu, u64 *sptep)
 static int host_pfn_mapping_level(struct kvm *kvm, gfn_t gfn, kvm_pfn_t pfn,
 				  const struct kvm_memory_slot *slot)
 {
+	struct page *page = pfn_to_page(pfn);
+	int level = PG_LEVEL_4K;
 	unsigned long hva;
 	unsigned long flags;
-	int level = PG_LEVEL_4K;
 	pgd_t pgd;
 	p4d_t p4d;
 	pud_t pud;
 	pmd_t pmd;
 
-	if (!PageCompound(pfn_to_page(pfn)) && !kvm_is_zone_device_pfn(pfn))
+	if (!PageCompound(page) && !kvm_is_zone_device_page(page))
 		return PG_LEVEL_4K;
 
 	/*

include/linux/kvm_host.h

@@ -1571,7 +1571,7 @@ void kvm_arch_sync_events(struct kvm *kvm);
 int kvm_cpu_has_pending_timer(struct kvm_vcpu *vcpu);
 
 bool kvm_is_reserved_pfn(kvm_pfn_t pfn);
-bool kvm_is_zone_device_pfn(kvm_pfn_t pfn);
+bool kvm_is_zone_device_page(struct page *page);
 
 struct kvm_irq_ack_notifier {
 	struct hlist_node link;

virt/kvm/kvm_main.c

@@ -168,7 +168,7 @@ __weak void kvm_arch_guest_memory_reclaimed(struct kvm *kvm)
 {
 }
 
-bool kvm_is_zone_device_pfn(kvm_pfn_t pfn)
+bool kvm_is_zone_device_page(struct page *page)
 {
 	/*
 	 * The metadata used by is_zone_device_page() to determine whether or
@@ -176,10 +176,10 @@ bool kvm_is_zone_device_pfn(kvm_pfn_t pfn)
 	 * the device has been pinned, e.g. by get_user_pages().  WARN if the
 	 * page_count() is zero to help detect bad usage of this helper.
 	 */
-	if (!pfn_valid(pfn) || WARN_ON_ONCE(!page_count(pfn_to_page(pfn))))
+	if (WARN_ON_ONCE(!page_count(page)))
 		return false;
 
-	return is_zone_device_page(pfn_to_page(pfn));
+	return is_zone_device_page(page);
 }
 
 bool kvm_is_reserved_pfn(kvm_pfn_t pfn)
@@ -192,7 +192,7 @@ bool kvm_is_reserved_pfn(kvm_pfn_t pfn)
 	if (pfn_valid(pfn))
 		return PageReserved(pfn_to_page(pfn)) &&
 		       !is_zero_pfn(pfn) &&
-		       !kvm_is_zone_device_pfn(pfn);
+		       !kvm_is_zone_device_page(pfn_to_page(pfn));
 
 	return true;
 }