KVM: PPC: Book3S HV: Fix calculation of guest phys address for MMIO emulation

In the case where the host kernel is using a 64kB base page size and
the guest uses a 4k HPTE (hashed page table entry) to map an emulated
MMIO device, we were calculating the guest physical address wrongly.
We were calculating a gfn as the guest physical address shifted right
16 bits (PAGE_SHIFT) but then only adding back in 12 bits from the
effective address, since the HPTE had a 4k page size.  Thus the gpa
reported to userspace was missing 4 bits.

Instead, we now compute the guest physical address from the HPTE
without reference to the host page size, and then compute the gfn
by shifting the gpa right PAGE_SHIFT bits.

Reported-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Alexander Graf <agraf@suse.de>

arch/powerpc/kvm/book3s_64_mmu_hv.c

@@ -571,7 +571,7 @@ int kvmppc_book3s_hv_page_fault(struct kvm_run *run, struct kvm_vcpu *vcpu,
 	struct kvm *kvm = vcpu->kvm;
 	unsigned long *hptep, hpte[3], r;
 	unsigned long mmu_seq, psize, pte_size;
-	unsigned long gfn, hva, pfn;
+	unsigned long gpa, gfn, hva, pfn;
 	struct kvm_memory_slot *memslot;
 	unsigned long *rmap;
 	struct revmap_entry *rev;
@@ -609,15 +609,14 @@ int kvmppc_book3s_hv_page_fault(struct kvm_run *run, struct kvm_vcpu *vcpu,
 
 	/* Translate the logical address and get the page */
 	psize = hpte_page_size(hpte[0], r);
-	gfn = hpte_rpn(r, psize);
+	gpa = (r & HPTE_R_RPN & ~(psize - 1)) | (ea & (psize - 1));
+	gfn = gpa >> PAGE_SHIFT;
 	memslot = gfn_to_memslot(kvm, gfn);
 
 	/* No memslot means it's an emulated MMIO region */
-	if (!memslot || (memslot->flags & KVM_MEMSLOT_INVALID)) {
-		unsigned long gpa = (gfn << PAGE_SHIFT) | (ea & (psize - 1));
+	if (!memslot || (memslot->flags & KVM_MEMSLOT_INVALID))
 		return kvmppc_hv_emulate_mmio(run, vcpu, gpa, ea,
 					      dsisr & DSISR_ISSTORE);
-	}
 
 	if (!kvm->arch.using_mmu_notifiers)
 		return -EFAULT;		/* should never get here */