[PATCH 0/4] KVM: selftests: Improve error handling when opening files

[PATCH 0/4] KVM: selftests: Improve error handling when opening files

[Sean Christopherson]

Improve selftests' error reporting when opening a file fails, e.g. so that
failure to access a module param spits out a message about KVM not being
loaded, instead of a cryptic message about a param not being supported.

Sean Christopherson (4):
  KVM: selftests: Verify KVM is loaded when getting a KVM module param
  KVM: selftests: Add __open_path_or_exit() variant to provide extra
    help info
  KVM: selftests: Play nice with EACCES errors in open_path_or_exit()
  KVM: selftests: Print a more helpful message for EACCESS in access
    tracking test

 .../selftests/kvm/access_tracking_perf_test.c |  7 ++----
 .../testing/selftests/kvm/include/kvm_util.h  |  1 +
 .../selftests/kvm/include/x86/processor.h     |  6 ++++-
 tools/testing/selftests/kvm/lib/kvm_util.c    | 23 +++++++++++++++----
 .../testing/selftests/kvm/lib/x86/processor.c | 10 --------
 .../vmx_exception_with_invalid_guest_state.c  |  2 +-
 6 files changed, 28 insertions(+), 21 deletions(-)


base-commit: 7ef51a41466bc846ad794d505e2e34ff97157f7f
-- 
2.49.0.1112.g889b7c5bd8-goog

[PATCH 1/4] KVM: selftests: Verify KVM is loaded when getting a KVM module param

[Sean Christopherson]

Probe /dev/kvm when getting a KVM module param so that attempting to load
a module param super early in a selftest generates a SKIP message about
KVM not being loaded/enabled, versus some random parameter not existing.

E.g. KVM x86's unconditional retrieval of force_emulation_prefix during
kvm_selftest_arch_init() generates a rather confusing error message that
takes far too much triage to understand.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 tools/testing/selftests/kvm/include/x86/processor.h    |  6 +++++-
 tools/testing/selftests/kvm/lib/kvm_util.c             |  3 +++
 tools/testing/selftests/kvm/lib/x86/processor.c        | 10 ----------
 .../kvm/x86/vmx_exception_with_invalid_guest_state.c   |  2 +-
 4 files changed, 9 insertions(+), 12 deletions(-)

diff --git a/tools/testing/selftests/kvm/include/x86/processor.h b/tools/testing/selftests/kvm/include/x86/processor.h
index b11b5a53ebd5..2efb05c2f2fb 100644
--- a/tools/testing/selftests/kvm/include/x86/processor.h
+++ b/tools/testing/selftests/kvm/include/x86/processor.h
@@ -1150,7 +1150,6 @@ do {											\
 
 void kvm_get_cpu_address_width(unsigned int *pa_bits, unsigned int *va_bits);
 void kvm_init_vm_address_properties(struct kvm_vm *vm);
-bool vm_is_unrestricted_guest(struct kvm_vm *vm);
 
 struct ex_regs {
 	uint64_t rax, rcx, rdx, rbx;
@@ -1325,6 +1324,11 @@ static inline bool kvm_is_forced_emulation_enabled(void)
 	return !!get_kvm_param_integer("force_emulation_prefix");
 }
 
+static inline bool kvm_is_unrestricted_guest_enabled(void)
+{
+	return get_kvm_intel_param_bool("unrestricted_guest");
+}
+
 uint64_t *__vm_get_page_table_entry(struct kvm_vm *vm, uint64_t vaddr,
 				    int *level);
 uint64_t *vm_get_page_table_entry(struct kvm_vm *vm, uint64_t vaddr);
diff --git a/tools/testing/selftests/kvm/lib/kvm_util.c b/tools/testing/selftests/kvm/lib/kvm_util.c
index 50edc59cc0ca..b21ba80e3015 100644
--- a/tools/testing/selftests/kvm/lib/kvm_util.c
+++ b/tools/testing/selftests/kvm/lib/kvm_util.c
@@ -64,6 +64,9 @@ static ssize_t get_module_param(const char *module_name, const char *param,
 	ssize_t bytes_read;
 	int fd, r;
 
+	/* Verify KVM is loaded, to provide a more helpful SKIP message. */
+	close(open_kvm_dev_path_or_exit());
+
 	r = snprintf(path, path_size, "/sys/module/%s/parameters/%s",
 		     module_name, param);
 	TEST_ASSERT(r < path_size,
diff --git a/tools/testing/selftests/kvm/lib/x86/processor.c b/tools/testing/selftests/kvm/lib/x86/processor.c
index a92dc1dad085..d4c19ac885a9 100644
--- a/tools/testing/selftests/kvm/lib/x86/processor.c
+++ b/tools/testing/selftests/kvm/lib/x86/processor.c
@@ -1264,16 +1264,6 @@ unsigned long vm_compute_max_gfn(struct kvm_vm *vm)
 	return min(max_gfn, ht_gfn - 1);
 }
 
-/* Returns true if kvm_intel was loaded with unrestricted_guest=1. */
-bool vm_is_unrestricted_guest(struct kvm_vm *vm)
-{
-	/* Ensure that a KVM vendor-specific module is loaded. */
-	if (vm == NULL)
-		close(open_kvm_dev_path_or_exit());
-
-	return get_kvm_intel_param_bool("unrestricted_guest");
-}
-
 void kvm_selftest_arch_init(void)
 {
 	host_cpu_is_intel = this_cpu_is_intel();
diff --git a/tools/testing/selftests/kvm/x86/vmx_exception_with_invalid_guest_state.c b/tools/testing/selftests/kvm/x86/vmx_exception_with_invalid_guest_state.c
index 3fd6eceab46f..2cae86d9d5e2 100644
--- a/tools/testing/selftests/kvm/x86/vmx_exception_with_invalid_guest_state.c
+++ b/tools/testing/selftests/kvm/x86/vmx_exception_with_invalid_guest_state.c
@@ -110,7 +110,7 @@ int main(int argc, char *argv[])
 	struct kvm_vm *vm;
 
 	TEST_REQUIRE(host_cpu_is_intel);
-	TEST_REQUIRE(!vm_is_unrestricted_guest(NULL));
+	TEST_REQUIRE(!kvm_is_unrestricted_guest_enabled());
 
 	vm = vm_create_with_one_vcpu(&vcpu, guest_code);
 	get_set_sigalrm_vcpu(vcpu);
-- 
2.49.0.1112.g889b7c5bd8-goog

[PATCH 2/4] KVM: selftests: Add __open_path_or_exit() variant to provide extra help info

[Sean Christopherson]

Add an inner __open_path_or_exit() API to let the caller provide additional
information on ENOENT to try and help the user figure out why the test is
being skipped, e.g. for files like the page_idle bitmap needed by the
access tracking perf, which is dependent on a Kconfig.

Immediately convert /dev/kvm to the new API, both as an example and because
users might not know that some architectures/setups require loading KVM.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 .../testing/selftests/kvm/include/kvm_util.h  |  1 +
 tools/testing/selftests/kvm/lib/kvm_util.c    | 19 +++++++++++++++----
 2 files changed, 16 insertions(+), 4 deletions(-)

diff --git a/tools/testing/selftests/kvm/include/kvm_util.h b/tools/testing/selftests/kvm/include/kvm_util.h
index a1fc52bbdf7a..ee29e5d0c5ad 100644
--- a/tools/testing/selftests/kvm/include/kvm_util.h
+++ b/tools/testing/selftests/kvm/include/kvm_util.h
@@ -247,6 +247,7 @@ struct vm_guest_mode_params {
 };
 extern const struct vm_guest_mode_params vm_guest_mode_params[];
 
+int __open_path_or_exit(const char *path, int flags, const char *enoent_help);
 int open_path_or_exit(const char *path, int flags);
 int open_kvm_dev_path_or_exit(void);
 
diff --git a/tools/testing/selftests/kvm/lib/kvm_util.c b/tools/testing/selftests/kvm/lib/kvm_util.c
index b21ba80e3015..b133f2b1dbf7 100644
--- a/tools/testing/selftests/kvm/lib/kvm_util.c
+++ b/tools/testing/selftests/kvm/lib/kvm_util.c
@@ -26,15 +26,26 @@ static uint32_t last_guest_seed;
 
 static int vcpu_mmap_sz(void);
 
-int open_path_or_exit(const char *path, int flags)
+int __open_path_or_exit(const char *path, int flags, const char *enoent_help)
 {
 	int fd;
 
 	fd = open(path, flags);
-	__TEST_REQUIRE(fd >= 0 || errno != ENOENT, "Cannot open %s: %s", path, strerror(errno));
-	TEST_ASSERT(fd >= 0, "Failed to open '%s'", path);
+	if (fd < 0)
+		goto error;
 
 	return fd;
+
+error:
+	if (errno == ENOENT)
+		ksft_exit_skip("- Cannot open '%s': %s.  %s\n",
+			       path, strerror(errno), enoent_help);
+	TEST_FAIL("Failed to open '%s'", path);
+}
+
+int open_path_or_exit(const char *path, int flags)
+{
+	return __open_path_or_exit(path, flags, "");
 }
 
 /*
@@ -48,7 +59,7 @@ int open_path_or_exit(const char *path, int flags)
  */
 static int _open_kvm_dev_path_or_exit(int flags)
 {
-	return open_path_or_exit(KVM_DEV_PATH, flags);
+	return __open_path_or_exit(KVM_DEV_PATH, flags, "Is KVM loaded and enabled?");
 }
 
 int open_kvm_dev_path_or_exit(void)
-- 
2.49.0.1112.g889b7c5bd8-goog

[PATCH 3/4] KVM: selftests: Play nice with EACCES errors in open_path_or_exit()

[Sean Christopherson]

Expand the SKIP conditions of the open_path_or_exit() helper to skip on
EACCES as well as ENOENT.  Most often, lack of permissions to a file
needed by a KVM selftests is due to a file being root-only by default,
not because of any bug/misconfiguration that warrants failing a test.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 tools/testing/selftests/kvm/lib/kvm_util.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/kvm/lib/kvm_util.c b/tools/testing/selftests/kvm/lib/kvm_util.c
index b133f2b1dbf7..cd415f70de98 100644
--- a/tools/testing/selftests/kvm/lib/kvm_util.c
+++ b/tools/testing/selftests/kvm/lib/kvm_util.c
@@ -37,9 +37,10 @@ int __open_path_or_exit(const char *path, int flags, const char *enoent_help)
 	return fd;
 
 error:
-	if (errno == ENOENT)
+	if (errno == EACCES || errno == ENOENT)
 		ksft_exit_skip("- Cannot open '%s': %s.  %s\n",
-			       path, strerror(errno), enoent_help);
+			       path, strerror(errno),
+			       errno == EACCES ? "Root required?" : enoent_help);
 	TEST_FAIL("Failed to open '%s'", path);
 }
 
-- 
2.49.0.1112.g889b7c5bd8-goog

[PATCH 4/4] KVM: selftests: Print a more helpful message for EACCESS in access tracking test

[Sean Christopherson]

Use open_path_or_exit() helper to probe /sys/kernel/mm/page_idle/bitmap in
the access tracking perf test so that a helpful/pertinent SKIP message is
printed if the file exists but is inaccessible, e.g. because the file has
the kernel's default 0600 permissions.

Cc: James Houghton <jthoughton@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 tools/testing/selftests/kvm/access_tracking_perf_test.c | 7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/tools/testing/selftests/kvm/access_tracking_perf_test.c b/tools/testing/selftests/kvm/access_tracking_perf_test.c
index da7196fd1b23..c9de66537ec3 100644
--- a/tools/testing/selftests/kvm/access_tracking_perf_test.c
+++ b/tools/testing/selftests/kvm/access_tracking_perf_test.c
@@ -596,11 +596,8 @@ int main(int argc, char *argv[])
 		if (ret)
 			return ret;
 	} else {
-		page_idle_fd = open("/sys/kernel/mm/page_idle/bitmap", O_RDWR);
-		__TEST_REQUIRE(page_idle_fd >= 0,
-			       "Couldn't open /sys/kernel/mm/page_idle/bitmap. "
-			       "Is CONFIG_IDLE_PAGE_TRACKING enabled?");
-
+		page_idle_fd = __open_path_or_exit("/sys/kernel/mm/page_idle/bitmap", O_RDWR,
+						   "Is CONFIG_IDLE_PAGE_TRACKING enabled?");
 		close(page_idle_fd);
 
 		puts("Using page_idle for aging");
-- 
2.49.0.1112.g889b7c5bd8-goog

Re: [PATCH 0/4] KVM: selftests: Improve error handling when opening files

[Sean Christopherson]

On Fri, 16 May 2025 14:59:05 -0700, Sean Christopherson wrote:
> Improve selftests' error reporting when opening a file fails, e.g. so that
> failure to access a module param spits out a message about KVM not being
> loaded, instead of a cryptic message about a param not being supported.
> 
> Sean Christopherson (4):
>   KVM: selftests: Verify KVM is loaded when getting a KVM module param
>   KVM: selftests: Add __open_path_or_exit() variant to provide extra
>     help info
>   KVM: selftests: Play nice with EACCES errors in open_path_or_exit()
>   KVM: selftests: Print a more helpful message for EACCESS in access
>     tracking test
> 
> [...]

Applied to kvm-x86 selftests, thanks!

[1/4] KVM: selftests: Verify KVM is loaded when getting a KVM module param
      https://github.com/kvm-x86/linux/commit/fcab107abe1a
[2/4] KVM: selftests: Add __open_path_or_exit() variant to provide extra help info
      https://github.com/kvm-x86/linux/commit/6e1cce7cda1b
[3/4] KVM: selftests: Play nice with EACCES errors in open_path_or_exit()
      https://github.com/kvm-x86/linux/commit/ba300a728f6f
[4/4] KVM: selftests: Print a more helpful message for EACCESS in access tracking test
      https://github.com/kvm-x86/linux/commit/71443210e26d

--
https://github.com/kvm-x86/kvm-unit-tests/tree/next