On Mon, Jul 07, 2025, James Houghton wrote:
> + /*
> + * To time the jitter on all faults on pages that are not
> + * undergoing nx huge page recovery, only execute on every
> + * other 1G region, and only time the non-executing pass.
> + */
> + if (page & (1UL << 18)) {
This needs a #define or helper, I have no idea what 1 << 18 is doing.
> + uint64_t tsc1, tsc2;
> +
> + tsc1 = rdtsc();
> + *gva = 0;
> + tsc2 = rdtsc();
> +
> + if (tsc2 - tsc1 > max_cycles)
> + max_cycles = tsc2 - tsc1;
> + } else {
> + *gva = RETURN_OPCODE;
> + ((void (*)(void)) gva)();
> + }
> + }
> +
> + GUEST_SYNC1(max_cycles);
> +}
> +
> +struct kvm_vm *create_vm(uint64_t memory_bytes,
> + enum vm_mem_backing_src_type backing_src)
> +{
> + uint64_t backing_src_pagesz = get_backing_src_pagesz(backing_src);
> + struct guest_args *args = &guest_args;
> + uint64_t guest_num_pages;
> + uint64_t region_end_gfn;
> + uint64_t gpa, size;
> + struct kvm_vm *vm;
> +
> + args->guest_page_size = getpagesize();
> +
> + guest_num_pages = vm_adjust_num_guest_pages(VM_MODE_DEFAULT,
> + memory_bytes / args->guest_page_size);
> +
> + TEST_ASSERT(memory_bytes % getpagesize() == 0,
> + "Guest memory size is not host page size aligned.");
> +
> + vm = __vm_create_with_one_vcpu(&vcpu, guest_num_pages, guest_code);
> +
> + /* Put the test region at the top guest physical memory. */
> + region_end_gfn = vm->max_gfn + 1;
> +
> + /*
> + * If there should be more memory in the guest test region than there
> + * can be pages in the guest, it will definitely cause problems.
> + */
> + TEST_ASSERT(guest_num_pages < region_end_gfn,
> + "Requested more guest memory than address space allows.\n"
> + " guest pages: %" PRIx64 " max gfn: %" PRIx64
> + " wss: %" PRIx64 "]",
Don't wrap this last one.
> + guest_num_pages, region_end_gfn - 1, memory_bytes);
> +
> + gpa = (region_end_gfn - guest_num_pages - 1) * args->guest_page_size;
> + gpa = align_down(gpa, backing_src_pagesz);
> +
> + size = guest_num_pages * args->guest_page_size;
> + pr_info("guest physical test memory: [0x%lx, 0x%lx)\n",
> + gpa, gpa + size);
And don't wrap here either (82 chars is totally fine).
> +
> + /*
> + * Pass in MAP_POPULATE, because we are trying to test how long
> + * we have to wait for a pending NX huge page recovery to take.
> + * We do not want to also wait for GUP itself.
> + */
Right, but we also don't want to wait for the initial fault-in either, no? I.e.
plumbing in MAP_POPULATE only fixes the worst of the delay, and maybe only with
the TDP MMU enabled.
In other words, it seems like we need a helper (option?) to excplitly "prefault",
all memory from within the guest, not the ability to specify MAP_POPULATE.
> + vm_mem_add(vm, backing_src, gpa, 1,
> + guest_num_pages, 0, -1, 0, MAP_POPULATE);
> +
> + virt_map(vm, guest_test_virt_mem, gpa, guest_num_pages);
> +
> + args->pages = guest_num_pages;
> +
> + /* Export the shared variables to the guest. */
> + sync_global_to_guest(vm, guest_args);
> +
> + return vm;
> +}
> +
> +static void run_vcpu(struct kvm_vcpu *vcpu)
> +{
> + struct timespec ts_elapsed;
> + struct timespec ts_start;
> + struct ucall uc = {};
> + int ret;
> +
> + clock_gettime(CLOCK_MONOTONIC, &ts_start);
> +
> + ret = _vcpu_run(vcpu);
> +
> + ts_elapsed = timespec_elapsed(ts_start);
> +
> + TEST_ASSERT(ret == 0, "vcpu_run failed: %d", ret);
> +
> + TEST_ASSERT(get_ucall(vcpu, &uc) == UCALL_SYNC,
> + "Invalid guest sync status: %" PRIu64, uc.cmd);
> +
> + pr_info("Duration: %ld.%09lds\n",
> + ts_elapsed.tv_sec, ts_elapsed.tv_nsec);
> + pr_info("Max fault latency: %" PRIu64 " cycles\n", uc.args[0]);
> +}
> +
> +static void run_test(struct test_params *params)
> +{
> + /*
> + * The fault + execute pattern in the guest relies on having more than
> + * 1GiB to use.
> + */
> + TEST_ASSERT(params->memory_bytes > PAGE_SIZE << 18,
Oooh, the 1 << 18 is 1GiB on PFNs. Ugh. Just use SZ_1G here. And assert immediate
after setting params.memory_bytes, don't wait until the test runs.
> + "Must use more than 1GiB of memory.");
> +
> + create_vm(params->memory_bytes, params->backing_src);
> +
> + pr_info("\n");
> +
> + run_vcpu(vcpu);
> +}
> +
> +static void help(char *name)
> +{
> + puts("");
> + printf("usage: %s [-h] [-b bytes] [-s mem_type]\n",
> + name);
> + puts("");
> + printf(" -h: Display this help message.");
> + printf(" -b: specify the size of the memory region which should be\n"
> + " dirtied by the guest. e.g. 2048M or 3G.\n"
> + " (default: 2G, must be greater than 1G)\n");
> + backing_src_help("-s");
> + puts("");
> + exit(0);
> +}
> +
> +int main(int argc, char *argv[])
> +{
> + struct test_params params = {
> + .backing_src = DEFAULT_VM_MEM_SRC,
> + .memory_bytes = DEFAULT_TEST_MEM_SIZE,
> + };
> + int opt;
> +
> + while ((opt = getopt(argc, argv, "hb:s:")) != -1) {
> + switch (opt) {
> + case 'b':
> + params.memory_bytes = parse_size(optarg);
> + break;
> + case 's':
> + params.backing_src = parse_backing_src_type(optarg);
> + break;
> + case 'h':
> + default:
> + help(argv[0]);
> + break;
> + }
> + }
> +
> + run_test(¶ms);
> +}
> --
> 2.50.0.727.gbf7dc18ff4-goog
>
