KVM: MIPS/MMU: Invalidate GVA PTs on ASID changes

Implement invalidation of large ranges of virtual addresses from GVA
page tables in response to a guest ASID change (immediately for guest
kernel page table, lazily for guest user page table).

We iterate through a range of page tables invalidating entries and
freeing fully invalidated tables. To minimise overhead the exact ranges
invalidated depends on the flags argument to kvm_mips_flush_gva_pt(),
which also allows it to be used in future KVM_CAP_SYNC_MMU patches in
response to GPA changes, which unlike guest TLB mapping changes affects
guest KSeg0 mappings.

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

arch/mips/kvm/emulate.c

@@ -1171,6 +1171,17 @@ enum emulation_result kvm_mips_emulate_CP0(union mips_instruction inst,
 							& KVM_ENTRYHI_ASID,
 						nasid);
 
+					/*
+					 * Flush entries from the GVA page
+					 * tables.
+					 * Guest user page table will get
+					 * flushed lazily on re-entry to guest
+					 * user if the guest ASID actually
+					 * changes.
+					 */
+					kvm_mips_flush_gva_pt(kern_mm->pgd,
+							      KMF_KERN);
+
 					/*
 					 * Regenerate/invalidate kernel MMU
 					 * context.