On Mon, Nov 22, 2021, Vitaly Kuznetsov wrote:
> With the elevated 'KVM_CAP_MAX_VCPUS' value kvm_create_max_vcpus test
> may hit RLIMIT_NOFILE limits:
>
> # ./kvm_create_max_vcpus
> KVM_CAP_MAX_VCPU_ID: 4096
> KVM_CAP_MAX_VCPUS: 1024
> Testing creating 1024 vCPUs, with IDs 0...1023.
> /dev/kvm not available (errno: 24), skipping test
>
> Adjust RLIMIT_NOFILE limits to make sure KVM_CAP_MAX_VCPUS fds can be
> opened. Note, raising hard limit ('rlim_max') requires CAP_SYS_RESOURCE
> capability which is generally not needed to run kvm selftests (but without
> raising the limit the test is doomed to fail anyway).
>
> Signed-off-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
> ---
> .../selftests/kvm/kvm_create_max_vcpus.c | 22 +++++++++++++++++++
> 1 file changed, 22 insertions(+)
>
> diff --git a/tools/testing/selftests/kvm/kvm_create_max_vcpus.c b/tools/testing/selftests/kvm/kvm_create_max_vcpus.c
> index f968dfd4ee88..19198477a10e 100644
> --- a/tools/testing/selftests/kvm/kvm_create_max_vcpus.c
> +++ b/tools/testing/selftests/kvm/kvm_create_max_vcpus.c
> @@ -12,6 +12,7 @@
> #include <stdio.h>
> #include <stdlib.h>
> #include <string.h>
> +#include <sys/resource.h>
>
> #include "test_util.h"
>
> @@ -19,6 +20,9 @@
> #include "asm/kvm.h"
> #include "linux/kvm.h"
>
> +/* 'Safe' number of open file descriptors in addition to vCPU fds needed */
> +#define NOFD 16
Any reason not to make this "buffer" extra large, e.g. 100+ to avoid having to
debug this issue again in the future?
> +
> void test_vcpu_creation(int first_vcpu_id, int num_vcpus)
> {
> struct kvm_vm *vm;
> @@ -40,10 +44,28 @@ int main(int argc, char *argv[])
> {
> int kvm_max_vcpu_id = kvm_check_cap(KVM_CAP_MAX_VCPU_ID);
> int kvm_max_vcpus = kvm_check_cap(KVM_CAP_MAX_VCPUS);
Rather than a separate define that's hard to describe succintly, what about:
int nr_fds_wanted = kvm_max_vcpus + <arbitrary number>
and then the body becomes
if (nr_fds_wanted > rl.rlim_cur) {
rl.rlim_cur = nr_fds_wanted;
rl.rlim_max = max(rl.rlim_max, nr_fds_wanted);
...
}
> + struct rlimit rl;
>
> pr_info("KVM_CAP_MAX_VCPU_ID: %d\n", kvm_max_vcpu_id);
> pr_info("KVM_CAP_MAX_VCPUS: %d\n", kvm_max_vcpus);
>
> + /*
> + * Creating KVM_CAP_MAX_VCPUS vCPUs require KVM_CAP_MAX_VCPUS open
> + * file decriptors.
> + */
> + TEST_ASSERT(!getrlimit(RLIMIT_NOFILE, &rl),
> + "getrlimit() failed (errno: %d)", errno);
And strerror() output too?
> +
> + if (kvm_max_vcpus > rl.rlim_cur - NOFD) {
> + rl.rlim_cur = kvm_max_vcpus + NOFD;
> +
> + if (kvm_max_vcpus > rl.rlim_max - NOFD)
> + rl.rlim_max = kvm_max_vcpus + NOFD;
> +
> + TEST_ASSERT(!setrlimit(RLIMIT_NOFILE, &rl),
> + "setrlimit() failed (errno: %d)", errno);
> + }
> +
> /*
> * Upstream KVM prior to 4.8 does not support KVM_CAP_MAX_VCPU_ID.
> * Userspace is supposed to use KVM_CAP_MAX_VCPUS as the maximum ID
> --
> 2.33.1
>
