From feb84f6daa7e7d51444d13fa65df7d5562fd0075 Mon Sep 17 00:00:00 2001 From: Paolo Bonzini Date: Mon, 12 Dec 2022 05:36:53 -0500 Subject: KVM: selftests: document the default implementation of vm_vaddr_populate_bitmap Explain the meaning of the bit manipulations of vm_vaddr_populate_bitmap. These correspond to the "canonical addresses" of x86 and other architectures, but that is not obvious. Signed-off-by: Paolo Bonzini --- tools/testing/selftests/kvm/lib/kvm_util.c | 9 +++++++++ 1 file changed, 9 insertions(+) (limited to 'tools') diff --git a/tools/testing/selftests/kvm/lib/kvm_util.c b/tools/testing/selftests/kvm/lib/kvm_util.c index c88c3ace16d2..bd892a814951 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?"); +/* + * Initializes vm->vpages_valid to match the canonical VA space of the + * architecture. + * + * The default implementation is valid for architectures which 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]. + */ __weak void vm_vaddr_populate_bitmap(struct kvm_vm *vm) { sparsebit_set_num(vm->vpages_valid, -- cgit v1.2.3