KVM: PPC: Explicitly require struct page memory for Ultravisor sharing

Explicitly require "struct page" memory when sharing memory between
guest and host via an Ultravisor.  Given the number of pfn_to_page()
calls in the code, it's safe to assume that KVM already requires that the
pfn returned by gfn_to_pfn() is backed by struct page, i.e. this is
likely a bug fix, not a reduction in KVM capabilities.

Switching to gfn_to_page() will eventually allow removing gfn_to_pfn()
and kvm_pfn_to_refcounted_page().

Signed-off-by: Sean Christopherson <seanjc@google.com>
Tested-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <20241010182427.1434605-79-seanjc@google.com>

Author: sean-jc

arch/powerpc/kvm/book3s_hv_uvmem.c

@@ -879,9 +879,8 @@ static unsigned long kvmppc_share_page(struct kvm *kvm, unsigned long gpa,
 {
 
 	int ret = H_PARAMETER;
-	struct page *uvmem_page;
+	struct page *page, *uvmem_page;
 	struct kvmppc_uvmem_page_pvt *pvt;
-	unsigned long pfn;
 	unsigned long gfn = gpa >> page_shift;
 	int srcu_idx;
 	unsigned long uvmem_pfn;
@@ -901,8 +900,8 @@ static unsigned long kvmppc_share_page(struct kvm *kvm, unsigned long gpa,
 
 retry:
 	mutex_unlock(&kvm->arch.uvmem_lock);
-	pfn = gfn_to_pfn(kvm, gfn);
-	if (is_error_noslot_pfn(pfn))
+	page = gfn_to_page(kvm, gfn);
+	if (!page)
 		goto out;
 
 	mutex_lock(&kvm->arch.uvmem_lock);
@@ -911,16 +910,16 @@ static unsigned long kvmppc_share_page(struct kvm *kvm, unsigned long gpa,
 		pvt = uvmem_page->zone_device_data;
 		pvt->skip_page_out = true;
 		pvt->remove_gfn = false; /* it continues to be a valid GFN */
-		kvm_release_pfn_clean(pfn);
+		kvm_release_page_unused(page);
 		goto retry;
 	}
 
-	if (!uv_page_in(kvm->arch.lpid, pfn << page_shift, gpa, 0,
+	if (!uv_page_in(kvm->arch.lpid, page_to_pfn(page) << page_shift, gpa, 0,
 				page_shift)) {
 		kvmppc_gfn_shared(gfn, kvm);
 		ret = H_SUCCESS;
 	}
-	kvm_release_pfn_clean(pfn);
+	kvm_release_page_clean(page);
 	mutex_unlock(&kvm->arch.uvmem_lock);
 out:
 	srcu_read_unlock(&kvm->srcu, srcu_idx);
@@ -1083,21 +1082,21 @@ kvmppc_h_svm_page_out(struct kvm *kvm, unsigned long gpa,
 
 int kvmppc_send_page_to_uv(struct kvm *kvm, unsigned long gfn)
 {
-	unsigned long pfn;
+	struct page *page;
 	int ret = U_SUCCESS;
 
-	pfn = gfn_to_pfn(kvm, gfn);
-	if (is_error_noslot_pfn(pfn))
+	page = gfn_to_page(kvm, gfn);
+	if (!page)
 		return -EFAULT;
 
 	mutex_lock(&kvm->arch.uvmem_lock);
 	if (kvmppc_gfn_is_uvmem_pfn(gfn, kvm, NULL))
 		goto out;
 
-	ret = uv_page_in(kvm->arch.lpid, pfn << PAGE_SHIFT, gfn << PAGE_SHIFT,
-			 0, PAGE_SHIFT);
+	ret = uv_page_in(kvm->arch.lpid, page_to_pfn(page) << PAGE_SHIFT,
+			 gfn << PAGE_SHIFT, 0, PAGE_SHIFT);
 out:
-	kvm_release_pfn_clean(pfn);
+	kvm_release_page_clean(page);
 	mutex_unlock(&kvm->arch.uvmem_lock);
 	return (ret == U_SUCCESS) ? RESUME_GUEST : -EFAULT;
 }