KVM: selftests: Add helpers to pin pages with CONFIG_GUP_TEST

Add helper functions to allow KVM selftests to pin memory using
CONFIG_GUP_TEST. This is useful for creating test scenarios where some page
has an increased refcount, such as when testing guest_memfd in-place
conversion.

The helpers open /sys/kernel/debug/gup_test and invoke the
PIN_LONGTERM_TEST_START and PIN_LONGTERM_TEST_STOP ioctls. Since this
functionality depends on the kernel being built with CONFIG_GUP_TEST,
provide stub implementations that trigger a test failure if the
configuration is missing.

Signed-off-by: Ackerley Tng <ackerleytng@google.com>
Tested-by: Shivank Garg <shivankg@amd.com>
Reviewed-by: Fuad Tabba <tabba@google.com>
Tested-by: Yan Zhao <yan.y.zhao@intel.com>
Link: https://patch.msgid.link/20260910-gmem-inplace-conversion-v13-36-dd6fbf94f4e1@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

2 files changed, 28 insertions, 0 deletions

diff --git a/tools/testing/selftests/kvm/include/kvm_util.h b/tools/testing/selftests/kvm/include/kvm_util.h
index 575032e9791d..3cfe243d7c8b 100644
--- a/tools/testing/selftests/kvm/include/kvm_util.h
+++ b/tools/testing/selftests/kvm/include/kvm_util.h
@@ -1206,6 +1206,9 @@ static inline int pin_self_to_any_cpu(void)
 	return pin_task_to_any_cpu(pthread_self());
 }
 
+void pin_pages(void *vaddr, uint64_t size);
+void unpin_pages(void);
+
 void kvm_print_vcpu_pinning_help(void);
 void kvm_parse_vcpu_pinning(const char *pcpus_string, u32 vcpu_to_pcpu[],
 			    int nr_vcpus);
diff --git a/tools/testing/selftests/kvm/lib/kvm_util.c b/tools/testing/selftests/kvm/lib/kvm_util.c
index cd468b2bb834..b1456ed76e27 100644
--- a/tools/testing/selftests/kvm/lib/kvm_util.c
+++ b/tools/testing/selftests/kvm/lib/kvm_util.c
@@ -19,6 +19,8 @@
 #include <unistd.h>
 #include <linux/kernel.h>
 
+#include "../../../../../mm/gup_test.h"
+
 #define KVM_UTIL_MIN_PFN	2
 
 u32 kvm_random_seed;
@@ -645,6 +647,29 @@ int __pin_task_to_cpu(pthread_t task, int cpu)
 	return pthread_setaffinity_np(task, sizeof(cpuset), &cpuset);
 }
 
+static int gup_test_fd = -1;
+
+void pin_pages(void *vaddr, uint64_t size)
+{
+	const struct pin_longterm_test args = {
+		.addr = (uint64_t)vaddr,
+		.size = size,
+		.flags = PIN_LONGTERM_TEST_FLAG_USE_WRITE,
+	};
+
+	gup_test_fd = __open_path_or_exit("/sys/kernel/debug/gup_test", O_RDWR,
+					  "Is CONFIG_GUP_TEST enabled?");
+
+	TEST_ASSERT_EQ(ioctl(gup_test_fd, PIN_LONGTERM_TEST_START, &args), 0);
+}
+
+void unpin_pages(void)
+{
+	TEST_ASSERT_EQ(ioctl(gup_test_fd, PIN_LONGTERM_TEST_STOP), 0);
+
+	kvm_free_fd(gup_test_fd);
+}
+
 static u32 parse_pcpu(const char *cpu_str, const cpu_set_t *allowed_mask)
 {
 	u32 pcpu = atoi_non_negative("CPU number", cpu_str);