[PATCH 2/9] KVM: selftests: Add __packed attribute fallback

[PATCH 2/9] KVM: selftests: Add __packed attribute fallback

[Aqib Faruqui]

Kernel UAPI headers use __packed but don't provide the definition in
userspace builds.

Add a fallback definition matching the kernel's implementation. This
follows the same pattern used by BPF and SGX selftests.

Signed-off-by: Aqib Faruqui <aqibaf@amazon.com>
---
 tools/testing/selftests/kvm/include/kvm_util.h | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/tools/testing/selftests/kvm/include/kvm_util.h b/tools/testing/selftests/kvm/include/kvm_util.h
index 23a506d7e..7fae7f5e7 100644
--- a/tools/testing/selftests/kvm/include/kvm_util.h
+++ b/tools/testing/selftests/kvm/include/kvm_util.h
@@ -5,6 +5,10 @@
 #ifndef SELFTEST_KVM_UTIL_H
 #define SELFTEST_KVM_UTIL_H
 
+#ifndef __packed
+#define __packed __attribute__((__packed__))
+#endif
+
 #include "test_util.h"
 
 #include <linux/compiler.h>
-- 
2.47.3

Re: [PATCH 2/9] KVM: selftests: Add __packed attribute fallback

[Sean Christopherson]

On Fri, Aug 29, 2025, Aqib Faruqui wrote:
> Kernel UAPI headers use __packed but don't provide the definition in
> userspace builds.
> 
> Add a fallback definition matching the kernel's implementation. This
> follows the same pattern used by BPF and SGX selftests.

Ugh.  No, this needs to be fixed in a central location, not splattered all over
random subsystem selftests.  My first choice would be to copy (and keep synchronize)
all of the include/linux/compiler*.h headers to tools/include/linux/.

If for some reason that's not a viable option, we should yank the __packed and
similar #defines out of tools/include/linux/compiler-gcc.h and place them in
tools/include/linux/compiler.h.  AFAICT, none of them are actually GCC-only.

> Signed-off-by: Aqib Faruqui <aqibaf@amazon.com>
> ---
>  tools/testing/selftests/kvm/include/kvm_util.h | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/tools/testing/selftests/kvm/include/kvm_util.h b/tools/testing/selftests/kvm/include/kvm_util.h
> index 23a506d7e..7fae7f5e7 100644
> --- a/tools/testing/selftests/kvm/include/kvm_util.h
> +++ b/tools/testing/selftests/kvm/include/kvm_util.h
> @@ -5,6 +5,10 @@
>  #ifndef SELFTEST_KVM_UTIL_H
>  #define SELFTEST_KVM_UTIL_H
>  
> +#ifndef __packed
> +#define __packed __attribute__((__packed__))
> +#endif
> +
>  #include "test_util.h"
>  
>  #include <linux/compiler.h>
> -- 
> 2.47.3
> 

Re: [PATCH 2/9] KVM: selftests: Add __packed attribute fallback

[Faruqui, Aqib]

After investigating a little, looks like tools/include/linux/compiler.h already defines __packed correctly. While UAPI headers (e.g. linux/kvm.h) use __packed but don't include it themselves, the include ordering looks fine for this to be handled by the build system.

I'll drop this patch and investigate further why the tools infrastructure isn't working correctly in my setup.

Thanks for the feedback!

-- 
Aqib Faruqui 
Software Dev Intern (Embedded) | EC2 Accelerated Nitro | AWS 
+44 7763104413 




On 29/08/2025, 23:48, "Sean Christopherson" <seanjc@google.com <mailto:seanjc@google.com>> wrote:


CAUTION: This email originated from outside of the organization. Do not click links or open attachments unless you can confirm the sender and know the content is safe.






On Fri, Aug 29, 2025, Aqib Faruqui wrote:
> Kernel UAPI headers use __packed but don't provide the definition in
> userspace builds.
>
> Add a fallback definition matching the kernel's implementation. This
> follows the same pattern used by BPF and SGX selftests.


Ugh. No, this needs to be fixed in a central location, not splattered all over
random subsystem selftests. My first choice would be to copy (and keep synchronize)
all of the include/linux/compiler*.h headers to tools/include/linux/.


If for some reason that's not a viable option, we should yank the __packed and
similar #defines out of tools/include/linux/compiler-gcc.h and place them in
tools/include/linux/compiler.h. AFAICT, none of them are actually GCC-only.


> Signed-off-by: Aqib Faruqui <aqibaf@amazon.com <mailto:aqibaf@amazon.com>>
> ---
> tools/testing/selftests/kvm/include/kvm_util.h | 4 ++++
> 1 file changed, 4 insertions(+)
>
> diff --git a/tools/testing/selftests/kvm/include/kvm_util.h b/tools/testing/selftests/kvm/include/kvm_util.h
> index 23a506d7e..7fae7f5e7 100644
> --- a/tools/testing/selftests/kvm/include/kvm_util.h
> +++ b/tools/testing/selftests/kvm/include/kvm_util.h
> @@ -5,6 +5,10 @@
> #ifndef SELFTEST_KVM_UTIL_H
> #define SELFTEST_KVM_UTIL_H
>
> +#ifndef __packed
> +#define __packed __attribute__((__packed__))
> +#endif
> +
> #include "test_util.h"
>
> #include <linux/compiler.h>
> --
> 2.47.3
>

[PATCH 3/9] KVM: selftests: Add pthread_attr_setaffinity_np fallback

[Aqib Faruqui]

The pthread_attr_setaffinity_np function is a GNU extension that may not
be available in non-glibc C libraries. Some KVM selftests use this
function for CPU affinity control.

Add a function declaration and weak stub implementation for non-glibc
builds. This allows tests to build, with the affinity setting being a
no-op and errno set for the caller when the actual function is not available.

Signed-off-by: Aqib Faruqui <aqibaf@amazon.com>
---
 tools/testing/selftests/kvm/include/kvm_util.h |  4 ++++
 tools/testing/selftests/kvm/lib/kvm_util.c     | 11 +++++++++++
 2 files changed, 15 insertions(+)

diff --git a/tools/testing/selftests/kvm/include/kvm_util.h b/tools/testing/selftests/kvm/include/kvm_util.h
index 7fae7f5e7..8177178b5 100644
--- a/tools/testing/selftests/kvm/include/kvm_util.h
+++ b/tools/testing/selftests/kvm/include/kvm_util.h
@@ -31,6 +31,10 @@
 #include "kvm_util_types.h"
 #include "sparsebit.h"
 
+#ifndef __GLIBC__
+int pthread_attr_setaffinity_np(pthread_attr_t *attr, size_t cpusetsize, const cpu_set_t *cpuset);
+#endif /* __GLIBC__ */
+
 #define KVM_DEV_PATH "/dev/kvm"
 #define KVM_MAX_VCPUS 512
 
diff --git a/tools/testing/selftests/kvm/lib/kvm_util.c b/tools/testing/selftests/kvm/lib/kvm_util.c
index c3f5142b0..5ce80303d 100644
--- a/tools/testing/selftests/kvm/lib/kvm_util.c
+++ b/tools/testing/selftests/kvm/lib/kvm_util.c
@@ -20,6 +20,17 @@
 
 #define KVM_UTIL_MIN_PFN	2
 
+#ifndef __GLIBC__
+int __attribute__((weak))
+pthread_attr_setaffinity_np(pthread_attr_t *__attr,
+				size_t __cpusetsize,
+				const cpu_set_t *__cpuset)
+{
+	errno = ENOSYS;
+	return -1;
+}
+#endif
+
 uint32_t guest_random_seed;
 struct guest_random_state guest_rng;
 static uint32_t last_guest_seed;
-- 
2.47.3

Re: [PATCH 3/9] KVM: selftests: Add pthread_attr_setaffinity_np fallback

[Sean Christopherson]

On Fri, Aug 29, 2025, Aqib Faruqui wrote:
> The pthread_attr_setaffinity_np function is a GNU extension that may not
> be available in non-glibc C libraries. Some KVM selftests use this
> function for CPU affinity control.
> 
> Add a function declaration and weak stub implementation for non-glibc
> builds. This allows tests to build, with the affinity setting being a
> no-op and errno set for the caller when the actual function is not available.

Except this isn't a fallback, for all intents and purposes it silently breaks
the test.  A "fallback" is generally something that provides roughly equivalent
functionality.  This particular test will still pass because forced preemption
isn't strictly necessary, but this is still gross.  

Luckily, KVM selftests already provides APIs to pin tasks, just use those and
the problem naturally goes away.

--
From: Sean Christopherson <seanjc@google.com>
Date: Fri, 29 Aug 2025 15:31:44 -0700
Subject: [PATCH] KVM: selftests: Use KVM's task pinning APIs in steal_time
 time

Use pin_self_to_cpu() and pin_task_to_cpu() to pin the vCPU thread and
the stealer thread to pCPU0 in the steal_time.  Eliminating the usage of
pthread_attr_setaffinity_np() in particular allows building the test
again non-glibc C libraries.

Reported-by: Aqib Faruqui <aqibaf@amazon.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 tools/testing/selftests/kvm/steal_time.c | 12 ++++--------
 1 file changed, 4 insertions(+), 8 deletions(-)

diff --git a/tools/testing/selftests/kvm/steal_time.c b/tools/testing/selftests/kvm/steal_time.c
index cce2520af720..663c99c81703 100644
--- a/tools/testing/selftests/kvm/steal_time.c
+++ b/tools/testing/selftests/kvm/steal_time.c
@@ -341,9 +341,7 @@ int main(int ac, char **av)
 {
 	struct kvm_vcpu *vcpus[NR_VCPUS];
 	struct kvm_vm *vm;
-	pthread_attr_t attr;
 	pthread_t thread;
-	cpu_set_t cpuset;
 	unsigned int gpages;
 	long stolen_time;
 	long run_delay;
@@ -353,11 +351,7 @@ int main(int ac, char **av)
 	verbose = ac > 1 && (!strncmp(av[1], "-v", 3) || !strncmp(av[1], "--verbose", 10));
 
 	/* Set CPU affinity so we can force preemption of the VCPU */
-	CPU_ZERO(&cpuset);
-	CPU_SET(0, &cpuset);
-	pthread_attr_init(&attr);
-	pthread_attr_setaffinity_np(&attr, sizeof(cpu_set_t), &cpuset);
-	pthread_setaffinity_np(pthread_self(), sizeof(cpu_set_t), &cpuset);
+	pin_self_to_cpu(0);
 
 	/* Create a VM and an identity mapped memslot for the steal time structure */
 	vm = vm_create_with_vcpus(NR_VCPUS, guest_code, vcpus);
@@ -389,7 +383,9 @@ int main(int ac, char **av)
 
 		/* Steal time from the VCPU. The steal time thread has the same CPU affinity as the VCPUs. */
 		run_delay = get_run_delay();
-		pthread_create(&thread, &attr, do_steal_time, NULL);
+		pthread_create(&thread, NULL, do_steal_time, NULL);
+		pin_task_to_cpu(thread, 0);
+
 		do
 			sched_yield();
 		while (get_run_delay() - run_delay < MIN_RUN_DELAY_NS);

base-commit: ecbcc2461839e848970468b44db32282e5059925
--

[PATCH 4/9] selftests: kselftest: Add memfd_create syscall compatibility

[Aqib Faruqui]

The memfd_create function and related MFD_* flags may not be available
in non-glibc C libraries. Some selftests use memfd_create for
memory backing operations.

Add fallback definitions for MFD_CLOEXEC and MFD_HUGETLB flags, and
provide a memfd_create wrapper.

Signed-off-by: Aqib Faruqui <aqibaf@amazon.com>
---
 tools/testing/selftests/kselftest.h        | 19 +++++++++++++++++++
 tools/testing/selftests/kvm/lib/kvm_util.c |  1 +
 2 files changed, 20 insertions(+)

diff --git a/tools/testing/selftests/kselftest.h b/tools/testing/selftests/kselftest.h
index c3b6d2604..f362c6766 100644
--- a/tools/testing/selftests/kselftest.h
+++ b/tools/testing/selftests/kselftest.h
@@ -57,6 +57,7 @@
 #include <string.h>
 #include <stdio.h>
 #include <sys/utsname.h>
+#include <sys/syscall.h>
 #endif
 
 #ifndef ARRAY_SIZE
@@ -80,6 +81,24 @@
 #endif
 #endif /* end arch */
 
+#ifndef MFD_CLOEXEC
+#define MFD_CLOEXEC 0x0001U
+#endif
+
+#ifndef MFD_HUGETLB
+#define MFD_HUGETLB 0x0004U
+#endif
+
+static inline int memfd_create(const char *name, unsigned int flags)
+{
+#ifdef __NR_memfd_create
+	return syscall(__NR_memfd_create, name, flags);
+#else
+	errno = ENOSYS;
+	return -1;
+#endif
+}
+
 /* define kselftest exit codes */
 #define KSFT_PASS  0
 #define KSFT_FAIL  1
diff --git a/tools/testing/selftests/kvm/lib/kvm_util.c b/tools/testing/selftests/kvm/lib/kvm_util.c
index 5ce80303d..cb5209f6a 100644
--- a/tools/testing/selftests/kvm/lib/kvm_util.c
+++ b/tools/testing/selftests/kvm/lib/kvm_util.c
@@ -15,6 +15,7 @@
 #include <sys/resource.h>
 #include <sys/types.h>
 #include <sys/stat.h>
+#include <sys/syscall.h>
 #include <unistd.h>
 #include <linux/kernel.h>
 
-- 
2.47.3

[PATCH 5/9] KVM: selftests: Prevent PAGE_SIZE redefinition on x86

[Aqib Faruqui]

Prevent PAGE_SIZE redefinition warnings that can occur due to namespace
pollution from included headers.

Add an #ifndef directive before defining PAGE_SIZE to avoid redefinition
conflicts.

Signed-off-by: Aqib Faruqui <aqibaf@amazon.com>
---
 tools/testing/selftests/kvm/include/x86/processor.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/tools/testing/selftests/kvm/include/x86/processor.h b/tools/testing/selftests/kvm/include/x86/processor.h
index 2efb05c2f..3f93d1b4f 100644
--- a/tools/testing/selftests/kvm/include/x86/processor.h
+++ b/tools/testing/selftests/kvm/include/x86/processor.h
@@ -368,7 +368,9 @@ static inline unsigned int x86_model(unsigned int eax)
 #define PHYSICAL_PAGE_MASK      GENMASK_ULL(51, 12)
 
 #define PAGE_SHIFT		12
+#ifndef PAGE_SIZE
 #define PAGE_SIZE		(1ULL << PAGE_SHIFT)
+#endif
 #define PAGE_MASK		(~(PAGE_SIZE-1) & PHYSICAL_PAGE_MASK)
 
 #define HUGEPAGE_SHIFT(x)	(PAGE_SHIFT + (((x) - 1) * 9))
-- 
2.47.3

Re: [PATCH 5/9] KVM: selftests: Prevent PAGE_SIZE redefinition on x86

[Sean Christopherson]

On Fri, Aug 29, 2025, Aqib Faruqui wrote:
> Prevent PAGE_SIZE redefinition warnings that can occur due to namespace
> pollution from included headers.
> 
> Add an #ifndef directive before defining PAGE_SIZE to avoid redefinition
> conflicts.

Please provide more details on what is causing the conflicts.  Blindly using a
PAGE_SIZE without _knowing_ it's aligned with PAGE_SHIFT and PHYSICAL_PAGE_MASK
is far from ideal.

> Signed-off-by: Aqib Faruqui <aqibaf@amazon.com>
> ---
>  tools/testing/selftests/kvm/include/x86/processor.h | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/tools/testing/selftests/kvm/include/x86/processor.h b/tools/testing/selftests/kvm/include/x86/processor.h
> index 2efb05c2f..3f93d1b4f 100644
> --- a/tools/testing/selftests/kvm/include/x86/processor.h
> +++ b/tools/testing/selftests/kvm/include/x86/processor.h
> @@ -368,7 +368,9 @@ static inline unsigned int x86_model(unsigned int eax)
>  #define PHYSICAL_PAGE_MASK      GENMASK_ULL(51, 12)
>  
>  #define PAGE_SHIFT		12
> +#ifndef PAGE_SIZE
>  #define PAGE_SIZE		(1ULL << PAGE_SHIFT)
> +#endif
>  #define PAGE_MASK		(~(PAGE_SIZE-1) & PHYSICAL_PAGE_MASK)
>  
>  #define HUGEPAGE_SHIFT(x)	(PAGE_SHIFT + (((x) - 1) * 9))
> -- 
> 2.47.3
> 

[PATCH 6/9] KVM: selftests: Add backtrace fallback

[Aqib Faruqui]

The backtrace() function is a GNU extension available in glibc but may
not be present in non-glibc libraries. KVM selftests use backtrace() for
error reporting and debugging.

Add conditional inclusion of execinfo.h only for glibc builds and
provide a weak stub implementation of backtrace() that returns 0 (stack
trace empty) for non-glibc systems.

Signed-off-by: Aqib Faruqui <aqibaf@amazon.com>
---
 tools/testing/selftests/kvm/lib/assert.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/kvm/lib/assert.c b/tools/testing/selftests/kvm/lib/assert.c
index b49690658..c9778dc6c 100644
--- a/tools/testing/selftests/kvm/lib/assert.c
+++ b/tools/testing/selftests/kvm/lib/assert.c
@@ -6,11 +6,19 @@
  */
 #include "test_util.h"
 
-#include <execinfo.h>
 #include <sys/syscall.h>
 
+#ifdef __GLIBC__
+#include <execinfo.h> /* backtrace */
+#endif
+
 #include "kselftest.h"
 
+int __attribute__((weak)) backtrace(void **buffer, int size)
+{
+	return 0;
+}
+
 /* Dumps the current stack trace to stderr. */
 static void __attribute__((noinline)) test_dump_stack(void);
 static void test_dump_stack(void)
-- 
2.47.3