MIPS: KVM/locore.S: Don't preserve host ASID around vcpu_run

MIPS KVM uses different ASIDs for guest execution than for the host.
The host ASID is saved on the stack when entering the guest with
__kvm_mips_vcpu_run(), and restored again before returning back to the
caller (exit to userland).

- This does not take into account that pre-emption may have taken place
  during that time, which may have started a new ASID cycle and resulted
  in that process' ASID being invalidated and reused.

- This does not take into account that the process may have migrated to
  a different CPU during that time, with a different ASID assignment
  since they are managed per-CPU.

- It is actually redundant, since the host ASID will be restored
  correctly by kvm_arch_vcpu_put(), which is called almost immediately
  after kvm_arch_vcpu_ioctl_run() returns.

Therefore drop this code from locore.S
Signed-off-by: James Hogan <james.hogan@imgtec.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Cc: Paul Burton <paul.burton@imgtec.com>
Cc: linux-mips@linux-mips.org
Cc: kvm@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/13206/Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/kvm/locore.S

@@ -32,7 +32,6 @@
     EXPORT(x);
 
 /* Overload, Danger Will Robinson!! */
-#define PT_HOST_ASID        PT_BVADDR
 #define PT_HOST_USERLOCAL   PT_EPC
 
 #define CP0_DDATA_LO        $28,3
@@ -104,11 +103,6 @@ FEXPORT(__kvm_mips_vcpu_run)
 	mfc0	v0, CP0_STATUS
 	LONG_S	v0, PT_STATUS(k1)
 
-	/* Save host ASID, shove it into the BVADDR location */
-	mfc0	v1, CP0_ENTRYHI
-	andi	v1, 0xff
-	LONG_S	v1, PT_HOST_ASID(k1)
-
 	/* Save DDATA_LO, will be used to store pointer to vcpu */
 	mfc0	v1, CP0_DDATA_LO
 	LONG_S	v1, PT_HOST_USERLOCAL(k1)
@@ -551,12 +545,6 @@ __kvm_mips_return_to_host:
 	LONG_L	k0, PT_HOST_USERLOCAL(k1)
 	mtc0	k0, CP0_DDATA_LO
 
-	/* Restore host ASID */
-	LONG_L	k0, PT_HOST_ASID(sp)
-	andi	k0, 0xff
-	mtc0	k0,CP0_ENTRYHI
-	ehb
-
 	/* Load context saved on the host stack */
 	LONG_L	$0, PT_R0(k1)
 	LONG_L	$1, PT_R1(k1)