Re: [PATCH 3/4] KVM: arm64: selftests: Align VA space allocator with TTBR0

Sean Christopherson
2022-12-08T00:18:22Z

On Wed, Dec 07, 2022, Oliver Upton wrote:
> diff --git a/tools/testing/selftests/kvm/lib/aarch64/processor.c b/tools/testing/selftests/kvm/lib/aarch64/processor.c
> index 316de70db91d..5972a23b2765 100644
> --- a/tools/testing/selftests/kvm/lib/aarch64/processor.c
> +++ b/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)

Add "arch" so that it's obvious this can be overidden? The "__weak" conveys that
for the implementation, but not for the call site. E.g. vm_arch_vaddr_populate_bitmap().

Actually, IIUC, the issue is that the high half isn't mapped (probably the wrong
terminology). I.e. the calculation for the low half stays the same, and the high
half just goes away.

> +{
> + /*
> + * 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);
> +}
> diff --git a/tools/testing/selftests/kvm/lib/kvm_util.c b/tools/testing/selftests/kvm/lib/kvm_util.c
> index e9607eb089be..c88c3ace16d2 100644
> --- a/tools/testing/selftests/kvm/lib/kvm_util.c
> +++ b/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);

Any objection to fixing up the formatting? Actually, we can do more than just
fix the indentation, e.g. the number of bits is identical, and documenting that
this does a high/low split would be helpful.

Together, what about? The #ifdef is a bit gross, especially around "hi_start",
but it's less duplicate code. And IMO, having things bundled in the same place
makes it a lot easier for newbies (to arm64 or kernel coding in general) to
understand what's going on and why arm64 is different.

---
tools/testing/selftests/kvm/lib/kvm_util.c | 23 +++++++++++++++++-----
1 file changed, 18 insertions(+), 5 deletions(-)

diff --git a/tools/testing/selftests/kvm/lib/kvm_util.c b/tools/testing/selftests/kvm/lib/kvm_util.c
index e9607eb089be..d6f2c17e3d40 100644
--- a/tools/testing/selftests/kvm/lib/kvm_util.c
+++ b/tools/testing/selftests/kvm/lib/kvm_util.c
@@ -186,6 +186,23 @@ 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?");

+static void vm_vaddr_populate_bitmap(struct kvm_vm *vm)
+{
+ /*
+ * All architectures supports splitting the virtual address space into
+ * a high and a low half. Populate both halves, except for arm64 which
+ * currently uses only TTBR0_EL1 (arbitrary selftests "logic"), i.e.
+ * only has a valid low half.
+ */
+ sparsebit_num_t nr_va_bits = (1ULL << (vm->va_bits - 1)) >> vm->page_shift;
+#ifndef __aarch64__
+ sparsebit_num_t hi_start = (~((1ULL << (vm->va_bits - 1)) - 1)) >> vm->page_shift
+
+ sparsebit_set_num(vm->vpages_valid, hi_start, nr_bits);
+#endif
+ sparsebit_set_num(vm->vpages_valid, 0, nr_va_bits);
+}
+
struct kvm_vm *____vm_create(enum vm_guest_mode mode)
{
struct kvm_vm *vm;
@@ -274,11 +291,7 @@ 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);

base-commit: 35aecc3289eebf193fd70a067ea448ae2f0bb9b9
--