Re: [PATCH v2 03/10] selftests: kvm: s390: Add s390x ucontrol test suite with hpage test

[Janosch Frank <frankja@linux.ibm.com>]

On 7/23/24 11:31, Christoph Schlameuss wrote:
> Add test suite to validate the s390x architecture specific ucontrol KVM
> interface.
> 
> Make use of the selftest test harness.
> 
> * uc_cap_hpage testcase verifies that a ucontrol VM cannot be run with
>    hugepages.
> 
> To allow testing of the ucontrol interface the kernel needs a
> non-default config containing CONFIG_KVM_S390_UCONTROL.
> This config needs to be set to built-in (y) as this cannot be built as
> module.
> 
> Signed-off-by: Christoph Schlameuss <schlameuss@linux.ibm.com>
> Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
> ---

[...]

> +#include "kselftest_harness.h"
> +#include "kvm_util.h"
> +
> +#include <linux/capability.h>
> +#include <linux/sizes.h>
> +
> +#define SYS_ADMIN_CAP 0x200000

This looked suspicious to me.
Surely this would be available in some form in capability.h since 
CAP_SYS_ADMIN is something that's regularly checked.

[...]

> +
> +/* so directly declare capget to check caps without libcap */
> +int capget(cap_user_header_t header, cap_user_data_t data);
> +
> +/**
> + * In order to create user controlled virtual machines on S390,
> + * check KVM_CAP_S390_UCONTROL and use the flag KVM_VM_S390_UCONTROL
> + * as privileged user (SYS_ADMIN).
> + */
> +void require_ucontrol_admin(void)
> +{
> +	struct __user_cap_data_struct data[_LINUX_CAPABILITY_U32S_3];
> +	struct __user_cap_header_struct hdr = {
> +		.version = _LINUX_CAPABILITY_VERSION_3,
> +	};
> +	int rc;
> +
> +	rc = capget(&hdr, data);
> +	TEST_ASSERT_EQ(0, rc);
> +	TEST_REQUIRE((data->effective & SYS_ADMIN_CAP) > 0);

And in fact capability.h does have defines which hide the magic constant:
data->effective & CAP_TO_MASK(CAP_SYS_ADMIN)


> +
> +	TEST_REQUIRE(kvm_has_cap(KVM_CAP_S390_UCONTROL));
> +}
> +