KVM: arm64: selftests: Align VA space allocator with TTBR0

An interesting feature of the Arm architecture is that the stage-1 MMU
supports two distinct VA regions, controlled by TTBR{0,1}_EL1. As KVM
selftests on arm64 only uses TTBR0_EL1, the VA space is constrained to
[0, 2^(va_bits-1)). This is different from other architectures that
allow for addressing low and high regions of the VA space from a single
page table.

KVM selftests' VA space allocator presumes the valid address range is
split between low and high memory based the MSB, which of course is a
poor match for arm64's TTBR0 region.

Allow architectures to override the default VA space layout. Make use of
the override to align vpages_valid with the behavior of TTBR0 on arm64.

Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
Message-Id: <20221207214809.489070-4-oliver.upton@linux.dev>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

tools/testing/selftests/kvm/include/kvm_util_base.h

@@ -408,6 +408,7 @@ void vm_mem_region_set_flags(struct kvm_vm *vm, uint32_t slot, uint32_t flags);
 void vm_mem_region_move(struct kvm_vm *vm, uint32_t slot, uint64_t new_gpa);
 void vm_mem_region_delete(struct kvm_vm *vm, uint32_t slot);
 struct kvm_vcpu *__vm_vcpu_add(struct kvm_vm *vm, uint32_t vcpu_id);
+void vm_populate_vaddr_bitmap(struct kvm_vm *vm);
 vm_vaddr_t vm_vaddr_unused_gap(struct kvm_vm *vm, size_t sz, vm_vaddr_t vaddr_min);
 vm_vaddr_t vm_vaddr_alloc(struct kvm_vm *vm, size_t sz, vm_vaddr_t vaddr_min);
 vm_vaddr_t __vm_vaddr_alloc(struct kvm_vm *vm, size_t sz, vm_vaddr_t vaddr_min,

tools/testing/selftests/kvm/lib/aarch64/processor.c

@@ -541,3 +541,13 @@ void kvm_selftest_arch_init(void)
 	 */
 	guest_modes_append_default();
 }
+
+void vm_vaddr_populate_bitmap(struct kvm_vm *vm)
+{
+	/*
+	 * arm64 selftests use only TTBR0_EL1, meaning that the valid VA space
+	 * is [0, 2^(64 - TCR_EL1.T0SZ)).
+	 */
+	sparsebit_set_num(vm->vpages_valid, 0,
+			  (1ULL << vm->va_bits) >> vm->page_shift);
+}

tools/testing/selftests/kvm/lib/kvm_util.c

@@ -186,6 +186,15 @@ const struct vm_guest_mode_params vm_guest_mode_params[] = {
 _Static_assert(sizeof(vm_guest_mode_params)/sizeof(struct vm_guest_mode_params) == NUM_VM_MODES,
 	       "Missing new mode params?");
 
+__weak void vm_vaddr_populate_bitmap(struct kvm_vm *vm)
+{
+	sparsebit_set_num(vm->vpages_valid,
+		0, (1ULL << (vm->va_bits - 1)) >> vm->page_shift);
+	sparsebit_set_num(vm->vpages_valid,
+		(~((1ULL << (vm->va_bits - 1)) - 1)) >> vm->page_shift,
+		(1ULL << (vm->va_bits - 1)) >> vm->page_shift);
+}
+
 struct kvm_vm *____vm_create(enum vm_guest_mode mode)
 {
 	struct kvm_vm *vm;
@@ -274,11 +283,7 @@ struct kvm_vm *____vm_create(enum vm_guest_mode mode)
 
 	/* Limit to VA-bit canonical virtual addresses. */
 	vm->vpages_valid = sparsebit_alloc();
-	sparsebit_set_num(vm->vpages_valid,
-		0, (1ULL << (vm->va_bits - 1)) >> vm->page_shift);
-	sparsebit_set_num(vm->vpages_valid,
-		(~((1ULL << (vm->va_bits - 1)) - 1)) >> vm->page_shift,
-		(1ULL << (vm->va_bits - 1)) >> vm->page_shift);
+	vm_vaddr_populate_bitmap(vm);
 
 	/* Limit physical addresses to PA-bits. */
 	vm->max_gfn = vm_compute_max_gfn(vm);