KVM: selftests: Add configurable demand paging delay

When running the demand paging test with the -u option, the User Fault
FD handler essentially adds an arbitrary delay to page fault resolution.
To enable better simulation of a real demand paging scenario, add a
configurable delay to the UFFD handler.

Reviewed-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Ben Gardon <bgardon@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/tools/testing/selftests/kvm/demand_paging_test.c b/tools/testing/selftests/kvm/demand_paging_test.c
index 6be9793..ab302e1 100644 (file)
--- a/tools/testing/selftests/kvm/demand_paging_test.c
+++ b/tools/testing/selftests/kvm/demand_paging_test.c
@@ -145,6 +145,7 @@ bool quit_uffd_thread;
 struct uffd_handler_args {
        int uffd;
        int pipefd;
+       useconds_t delay;
 };
 
 static void *uffd_handler_thread_fn(void *arg)
@@ -152,6 +153,7 @@ static void *uffd_handler_thread_fn(void *arg)
        struct uffd_handler_args *uffd_args = (struct uffd_handler_args *)arg;
        int uffd = uffd_args->uffd;
        int pipefd = uffd_args->pipefd;
+       useconds_t delay = uffd_args->delay;
        int64_t pages = 0;
 
        while (!quit_uffd_thread) {
@@ -212,6 +214,8 @@ static void *uffd_handler_thread_fn(void *arg)
                if (!(msg.event & UFFD_EVENT_PAGEFAULT))
                        continue;
 
+               if (delay)
+                       usleep(delay);
                addr =  msg.arg.pagefault.address;
                r = handle_uffd_page_request(uffd, addr);
                if (r < 0)
@@ -223,7 +227,8 @@ static void *uffd_handler_thread_fn(void *arg)
 }
 
 static int setup_demand_paging(struct kvm_vm *vm,
-                              pthread_t *uffd_handler_thread, int pipefd)
+                              pthread_t *uffd_handler_thread, int pipefd,
+                              useconds_t uffd_delay)
 {
        int uffd;
        struct uffdio_api uffdio_api;
@@ -264,6 +269,7 @@ static int setup_demand_paging(struct kvm_vm *vm,
 
        uffd_args.uffd = uffd;
        uffd_args.pipefd = pipefd;
+       uffd_args.delay = uffd_delay;
        pthread_create(uffd_handler_thread, NULL, uffd_handler_thread_fn,
                       &uffd_args);
 
@@ -273,7 +279,8 @@ static int setup_demand_paging(struct kvm_vm *vm,
 #define GUEST_MEM_SHIFT 30 /* 1G */
 #define PAGE_SHIFT_4K  12
 
-static void run_test(enum vm_guest_mode mode, bool use_uffd)
+static void run_test(enum vm_guest_mode mode, bool use_uffd,
+                    useconds_t uffd_delay)
 {
        pthread_t vcpu_thread;
        pthread_t uffd_handler_thread;
@@ -341,7 +348,8 @@ static void run_test(enum vm_guest_mode mode, bool use_uffd)
                r = pipe2(pipefd, O_CLOEXEC | O_NONBLOCK);
                TEST_ASSERT(!r, "Failed to set up pipefd");
 
-               r = setup_demand_paging(vm, &uffd_handler_thread, pipefd[0]);
+               r = setup_demand_paging(vm, &uffd_handler_thread, pipefd[0],
+                                       uffd_delay);
                if (r < 0)
                        exit(-r);
        }
@@ -395,7 +403,7 @@ static void help(char *name)
        int i;
 
        puts("");
-       printf("usage: %s [-h] [-m mode] [-u]\n", name);
+       printf("usage: %s [-h] [-m mode] [-u] [-d uffd_delay_usec]\n", name);
        printf(" -m: specify the guest mode ID to test\n"
               "     (default: test all supported modes)\n"
               "     This option may be used multiple times.\n"
@@ -404,7 +412,11 @@ static void help(char *name)
                printf("         %d:    %s%s\n", i, vm_guest_mode_string(i),
                       guest_modes[i].supported ? " (supported)" : "");
        }
-       printf(" -u: Use User Fault FD to handle vCPU page faults.\n");
+       printf(" -u: use User Fault FD to handle vCPU page\n"
+              "     faults.\n");
+       printf(" -d: add a delay in usec to the User Fault\n"
+              "     FD handler to simulate demand paging\n"
+              "     overheads. Ignored without -u.\n");
        puts("");
        exit(0);
 }
@@ -415,6 +427,7 @@ int main(int argc, char *argv[])
        unsigned int mode;
        int opt, i;
        bool use_uffd = false;
+       useconds_t uffd_delay = 0;
 
 #ifdef __x86_64__
        guest_mode_init(VM_MODE_PXXV48_4K, true, true);
@@ -437,7 +450,7 @@ int main(int argc, char *argv[])
        guest_mode_init(VM_MODE_P40V48_4K, true, true);
 #endif
 
-       while ((opt = getopt(argc, argv, "hm:u")) != -1) {
+       while ((opt = getopt(argc, argv, "hm:ud:")) != -1) {
                switch (opt) {
                case 'm':
                        if (!mode_selected) {
@@ -453,6 +466,11 @@ int main(int argc, char *argv[])
                case 'u':
                        use_uffd = true;
                        break;
+               case 'd':
+                       uffd_delay = strtoul(optarg, NULL, 0);
+                       TEST_ASSERT(uffd_delay >= 0,
+                                   "A negative UFFD delay is not supported.");
+                       break;
                case 'h':
                default:
                        help(argv[0]);
@@ -466,7 +484,7 @@ int main(int argc, char *argv[])
                TEST_ASSERT(guest_modes[i].supported,
                            "Guest mode ID %d (%s) not supported.",
                            i, vm_guest_mode_string(i));
-               run_test(i, use_uffd);
+               run_test(i, use_uffd, uffd_delay);
        }
 
        return 0;