KVM: MIPS: Add VZ & TE capabilities

Add new KVM_CAP_MIPS_VZ and KVM_CAP_MIPS_TE capabilities, and in order
to allow MIPS KVM to support VZ without confusing old users (which
expect the trap & emulate implementation), define and start checking
KVM_CREATE_VM type codes.

The codes available are:

 - KVM_VM_MIPS_TE = 0

   This is the current value expected from the user, and will create a
   VM using trap & emulate in user mode, confined to the user mode
   address space. This may in future become unavailable if the kernel is
   only configured to support VZ, in which case the EINVAL error will be
   returned and KVM_CAP_MIPS_TE won't be available even though
   KVM_CAP_MIPS_VZ is.

 - KVM_VM_MIPS_VZ = 1

   This can be provided when the KVM_CAP_MIPS_VZ capability is available
   to create a VM using VZ, with a fully virtualized guest virtual
   address space. If VZ support is unavailable in the kernel, the EINVAL
   error will be returned (although old kernels without the
   KVM_CAP_MIPS_VZ capability may well succeed and create a trap &
   emulate VM).

This is designed to allow the desired implementation (T&E vs VZ) to be
potentially chosen at runtime rather than being fixed in the kernel
configuration.
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: Jonathan Corbet <corbet@lwn.net>
Cc: linux-mips@linux-mips.org
Cc: kvm@vger.kernel.org
Cc: linux-doc@vger.kernel.org

Documentation/virtual/kvm/api.txt

@@ -115,12 +115,17 @@ will access the virtual machine's physical address space; offset zero
 corresponds to guest physical address zero.  Use of mmap() on a VM fd
 is discouraged if userspace memory allocation (KVM_CAP_USER_MEMORY) is
 available.
-You most certainly want to use 0 as machine type.
+You probably want to use 0 as machine type.
 
 In order to create user controlled virtual machines on S390, check
 KVM_CAP_S390_UCONTROL and use the flag KVM_VM_S390_UCONTROL as
 privileged user (CAP_SYS_ADMIN).
 
+To use hardware assisted virtualization on MIPS (VZ ASE) rather than
+the default trap & emulate implementation (which changes the virtual
+memory layout to fit in user mode), check KVM_CAP_MIPS_VZ and use the
+flag KVM_VM_MIPS_VZ.
+
 
 4.3 KVM_GET_MSR_INDEX_LIST
 
@@ -4147,3 +4152,43 @@ This capability, if KVM_CHECK_EXTENSION indicates that it is
 available, means that that the kernel can support guests using the
 hashed page table MMU defined in Power ISA V3.00 (as implemented in
 the POWER9 processor), including in-memory segment tables.
+
+8.5 KVM_CAP_MIPS_VZ
+
+Architectures: mips
+
+This capability, if KVM_CHECK_EXTENSION on the main kvm handle indicates that
+it is available, means that full hardware assisted virtualization capabilities
+of the hardware are available for use through KVM. An appropriate
+KVM_VM_MIPS_* type must be passed to KVM_CREATE_VM to create a VM which
+utilises it.
+
+If KVM_CHECK_EXTENSION on a kvm VM handle indicates that this capability is
+available, it means that the VM is using full hardware assisted virtualization
+capabilities of the hardware. This is useful to check after creating a VM with
+KVM_VM_MIPS_DEFAULT.
+
+The value returned by KVM_CHECK_EXTENSION should be compared against known
+values (see below). All other values are reserved. This is to allow for the
+possibility of other hardware assisted virtualization implementations which
+may be incompatible with the MIPS VZ ASE.
+
+ 0: The trap & emulate implementation is in use to run guest code in user
+    mode. Guest virtual memory segments are rearranged to fit the guest in the
+    user mode address space.
+
+ 1: The MIPS VZ ASE is in use, providing full hardware assisted
+    virtualization, including standard guest virtual memory segments.
+
+8.6 KVM_CAP_MIPS_TE
+
+Architectures: mips
+
+This capability, if KVM_CHECK_EXTENSION on the main kvm handle indicates that
+it is available, means that the trap & emulate implementation is available to
+run guest code in user mode, even if KVM_CAP_MIPS_VZ indicates that hardware
+assisted virtualisation is also available. KVM_VM_MIPS_TE (0) must be passed
+to KVM_CREATE_VM to create a VM which utilises it.
+
+If KVM_CHECK_EXTENSION on a kvm VM handle indicates that this capability is
+available, it means that the VM is using trap & emulate.

arch/mips/kvm/mips.c

@@ -107,6 +107,14 @@ void kvm_arch_check_processor_compat(void *rtn)
 
 int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
 {
+	switch (type) {
+	case KVM_VM_MIPS_TE:
+		break;
+	default:
+		/* Unsupported KVM type */
+		return -EINVAL;
+	};
+
 	/* Allocate page table to map GPA -> RPA */
 	kvm->arch.gpa_mm.pgd = kvm_pgd_alloc();
 	if (!kvm->arch.gpa_mm.pgd)
@@ -1038,6 +1046,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
 	case KVM_CAP_READONLY_MEM:
 	case KVM_CAP_SYNC_MMU:
 	case KVM_CAP_IMMEDIATE_EXIT:
+	case KVM_CAP_MIPS_TE:
 		r = 1;
 		break;
 	case KVM_CAP_COALESCED_MMIO:

include/uapi/linux/kvm.h

@@ -702,6 +702,10 @@ struct kvm_ppc_resize_hpt {
 #define KVM_VM_PPC_HV 1
 #define KVM_VM_PPC_PR 2
 
+/* on MIPS, 0 forces trap & emulate, 1 forces VZ ASE */
+#define KVM_VM_MIPS_TE		0
+#define KVM_VM_MIPS_VZ		1
+
 #define KVM_S390_SIE_PAGE_OFFSET 1
 
 /*
@@ -883,6 +887,8 @@ struct kvm_ppc_resize_hpt {
 #define KVM_CAP_PPC_MMU_RADIX 134
 #define KVM_CAP_PPC_MMU_HASH_V3 135
 #define KVM_CAP_IMMEDIATE_EXIT 136
+#define KVM_CAP_MIPS_VZ 137
+#define KVM_CAP_MIPS_TE 138
 
 #ifdef KVM_CAP_IRQ_ROUTING