MIPS: KVM: Include bit 31 in segment matches

When faulting guest addresses are matched against guest segments with
the KVM_GUEST_KSEGX() macro, change the mask to 0xe0000000 so as to
include bit 31.

This is mainly for safety's sake, as it prevents a rogue BadVAddr in the
host kseg2/kseg3 segments (e.g. 0xC*******) after a TLB exception from
matching the guest kseg0 segment (e.g. 0x4*******), triggering an
internal KVM error instead of allowing the corresponding guest kseg0
page to be mapped into the host vmalloc space.

Such a rogue BadVAddr was observed to happen with the host MIPS kernel
running under QEMU with KVM built as a module, due to a not entirely
transparent optimisation in the QEMU TLB handling. This has already been
worked around properly in a previous commit.
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: kvm@vger.kernel.org
Cc: linux-mips@linux-mips.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/mips/include/asm/kvm_host.h

@@ -74,7 +74,7 @@
 #define KVM_GUEST_KUSEG			0x00000000UL
 #define KVM_GUEST_KSEG0			0x40000000UL
 #define KVM_GUEST_KSEG23		0x60000000UL
-#define KVM_GUEST_KSEGX(a)		((_ACAST32_(a)) & 0x60000000)
+#define KVM_GUEST_KSEGX(a)		((_ACAST32_(a)) & 0xe0000000)
 #define KVM_GUEST_CPHYSADDR(a)		((_ACAST32_(a)) & 0x1fffffff)
 
 #define KVM_GUEST_CKSEG0ADDR(a)		(KVM_GUEST_CPHYSADDR(a) | KVM_GUEST_KSEG0)