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)). 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.

Add a helper that correctly handles both addressing schemes with a comment describing each.

Signed-off-by: Oliver Upton oliver.upton@linux.dev --- .../selftests/kvm/include/kvm_util_base.h | 1 + tools/testing/selftests/kvm/lib/kvm_util.c | 49 ++++++++++++++++--- 2 files changed, 44 insertions(+), 6 deletions(-)

diff --git a/tools/testing/selftests/kvm/include/kvm_util_base.h b/tools/testing/selftests/kvm/include/kvm_util_base.h index 6cd86da698b3..b193863d754f 100644 --- a/tools/testing/selftests/kvm/include/kvm_util_base.h +++ b/tools/testing/selftests/kvm/include/kvm_util_base.h @@ -103,6 +103,7 @@ struct kvm_vm { struct sparsebit *vpages_mapped; bool has_irqchip; bool pgd_created; + bool has_split_va_space; vm_paddr_t ucall_mmio_addr; vm_paddr_t pgd; vm_vaddr_t gdt; diff --git a/tools/testing/selftests/kvm/lib/kvm_util.c b/tools/testing/selftests/kvm/lib/kvm_util.c index a256ec67aff6..53d15f32f220 100644 --- a/tools/testing/selftests/kvm/lib/kvm_util.c +++ b/tools/testing/selftests/kvm/lib/kvm_util.c @@ -186,6 +186,43 @@ 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?");

+/* + * Initializes vm->vpages_valid to match the canonical VA space of the + * architecture. + * + * Most architectures split the range addressed by a single page table into a + * low and high region based on the MSB of the VA. On architectures with this + * behavior the VA region spans [0, 2^(va_bits - 1)), [-(2^(va_bits - 1), -1]. + * + * arm64 is a bit different from the rest of the crowd, as the low and high + * regions of the VA space are addressed by distinct paging structures + * (TTBR{0,1}_EL1). KVM selftests on arm64 only uses TTBR0_EL1, meaning that we + * only have a low VA region. As there is no VA split based on the MSB, the VA + * region spans [0, 2^va_bits). + */ +static void vm_vaddr_populate_bitmap(struct kvm_vm *vm) +{ + sparsebit_num_t contig_va_bits = vm->va_bits; + sparsebit_num_t nr_contig_pages; + + /* + * Depending on the architecture, the MSB of the VA could split between + * low and high regions. When that is the case each region has + * va_bits - 1 of address. + */ + if (vm->has_split_va_space) + contig_va_bits--; + + nr_contig_pages = (1ULL << contig_va_bits) >> vm->page_shift; + + sparsebit_set_num(vm->vpages_valid, 0, nr_contig_pages); + + if (vm->has_split_va_space) + sparsebit_set_num(vm->vpages_valid, + -(1ULL << contig_va_bits), + nr_contig_pages); +} + struct kvm_vm *____vm_create(enum vm_guest_mode mode) { struct kvm_vm *vm; @@ -268,17 +305,17 @@ struct kvm_vm *____vm_create(enum vm_guest_mode mode) #ifdef __aarch64__ if (vm->pa_bits != 40) vm->type = KVM_VM_TYPE_ARM_IPA_SIZE(vm->pa_bits); + + /* selftests use TTBR0 only, meaning there is a single VA region. */ + vm->has_split_va_space = false; +#else + vm->has_split_va_space = true; #endif

vm_open(vm);

- /* 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);