powerpc: kvm: Set M flag for KVM PTE depending on CPU_FTR_NEED_COHERENT

Usually page table entries only have the M (coherence) flag set, if the kernel is in SMP mode or to avoid data corruption due to CPU bugs (e.g. some 74xx CPUs). KVM on book3s_32 however always sets the M flag for a PTE, which locks up machines based on the amigaone platform when running QEMU or MoL.
Setting the M flag depending on CPU_FTR_NEED_COHERENT also makes KVM work on this platform and aligns the PTE setup to the rest of the kernel.

---
With this patch I could successfully run a Debian Wheezy installation inside QEMU started with --enable-kvm on my AmigaOneG3SE.

 arch/powerpc/kvm/book3s_32_mmu_host.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

index 2035d16..935c7d0 100644
@@ -204,7 +204,10 @@ next_pteg:
 
 	pteg0 = ((eaddr & 0x0fffffff) >> 22) | (vsid << 7) | PTE_V |
 		(primary ? 0 : PTE_SEC);
-	pteg1 = hpaddr | PTE_M | PTE_R | PTE_C;
+	pteg1 = hpaddr | PTE_R | PTE_C;
+
+	if (cpu_has_feature(CPU_FTR_NEED_COHERENT))
+		pteg1 |= PTE_M;
 
 	if (orig_pte->may_write && writable) {
 		pteg1 |= PP_RWRW;

1.9.1