KVM: PPC: Use kvm_vcpu_map() to map guest memory to patch dcbz instructions

Use kvm_vcpu_map() when patching dcbz in guest memory, as a regular GUP
isn't technically sufficient when writing to data in the target pages.
As per Documentation/core-api/pin_user_pages.rst:

Correct (uses FOLL_PIN calls):
pin_user_pages()
write to the data within the pages
unpin_user_pages()

INCORRECT (uses FOLL_GET calls):
get_user_pages()
write to the data within the pages
put_page()

As a happy bonus, using kvm_vcpu_{,un}map() takes care of creating a
mapping and marking the page dirty.

Signed-off-by: Sean Christopherson <[e-mail]>
Tested-by: Dmitry Osipenko <[e-mail]>
Signed-off-by: Paolo Bonzini <[e-mail]>
Message-ID: <[e-mail]>

arch/powerpc/kvm/book3s_pr.c

···
  */
 static void kvmppc_patch_dcbz(struct kvm_vcpu *vcpu, struct kvmppc_pte *pte)
 {
-	struct page *hpage;
+	struct kvm_host_map map;
 	u64 hpage_offset;
 	u32 *page;
-	int i;
+	int i, r;
 
-	hpage = gfn_to_page(vcpu->kvm, pte->raddr >> PAGE_SHIFT);
-	if (!hpage)
+	r = kvm_vcpu_map(vcpu, pte->raddr >> PAGE_SHIFT, &map);
+	if (r)
 		return;
 
 	hpage_offset = pte->raddr & ~PAGE_MASK;
 	hpage_offset &= ~0xFFFULL;
 	hpage_offset /= 4;
 
-	page = kmap_atomic(hpage);
+	page = map.hva;
 
 	/* patch dcbz into reserved instruction, so we trap */
 	for (i=hpage_offset; i < hpage_offset + (HW_PAGE_SIZE / 4); i++)
 		if ((be32_to_cpu(page[i]) & 0xff0007ff) == INS_DCBZ)
 			page[i] &= cpu_to_be32(0xfffffff7);
 
-	kunmap_atomic(page);
-	put_page(hpage);
+	kvm_vcpu_unmap(vcpu, &map);
 }
 
 static bool kvmppc_visible_gpa(struct kvm_vcpu *vcpu, gpa_t gpa)