MIPS: KVM: Use virt_to_phys() to get commpage PFN

Calculate the PFN of the commpage using virt_to_phys() instead of
CPHYSADDR(). This is more portable as kzalloc() may allocate from XKPhys
instead of KSeg0 on 64-bit kernels, which CPHYSADDR() doesn't handle.
This is sufficient for highmem kernels too since kzalloc() will allocate
from lowmem in KSeg0.

Signed-off-by: James Hogan <james.hogan@imgtec.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: "Radim Krčmář" <rkrcmar@redhat.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: linux-mips@linux-mips.org
Cc: kvm@vger.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/mips/kvm/tlb.c

@@ -176,7 +176,7 @@ int kvm_mips_handle_commpage_tlb_fault(unsigned long badvaddr,
 	unsigned long entrylo[2] = { 0, 0 };
 	unsigned int pair_idx;
 
-	pfn = CPHYSADDR(vcpu->arch.kseg0_commpage) >> PAGE_SHIFT;
+	pfn = PFN_DOWN(virt_to_phys(vcpu->arch.kseg0_commpage));
 	pair_idx = (badvaddr >> PAGE_SHIFT) & 1;
 	entrylo[pair_idx] = mips3_paddr_to_tlbpfn(pfn << PAGE_SHIFT) |
 		((_page_cachable_default >> _CACHE_SHIFT) << ENTRYLO_C_SHIFT) |