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>

diff --git a/arch/mips/kvm/locore.S b/arch/mips/kvm/locore.S
index 81687ab..c24facc 100644 (file)
--- a/arch/mips/kvm/locore.S
+++ b/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)