linux-kernel - Re: [PATCH v2] KVM: selftests: Make sure kvm_create_max_vcpus test won't hit RLIMIT

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Message-ID: <YZ6JWGCaDihh4KoG@google.com>
Date:   Wed, 24 Nov 2021 18:50:00 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:     kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] KVM: selftests: Make sure kvm_create_max_vcpus test
 won't hit RLIMIT_NOFILE

On Tue, Nov 23, 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@...hat.com>
> ---
> Changes since v1:
> - Drop 'NOFD' define replacing it with 'int nr_fds_wanted' [Sean]
> - Drop 'errno' printout as TEST_ASSERT() already does that.
> ---
>  .../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..ca957fe3f903 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"
>  
> @@ -40,10 +41,31 @@ 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);
> +	/*
> +	 * Number of file descriptors reqired, KVM_CAP_MAX_VCPUS for vCPU fds +
> +	 * an arbitrary number for everything else.
> +	 */
> +	int nr_fds_wanted = kvm_max_vcpus + 100;
> +	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);
>  
> +	/*
> +	 * Check that we're allowed to open nr_fds_wanted file descriptors and
> +	 * try raising the limits if needed.
> +	 */
> +	TEST_ASSERT(!getrlimit(RLIMIT_NOFILE, &rl), "getrlimit() failed!");
> +
> +	if (rl.rlim_cur < nr_fds_wanted) {
> +		rl.rlim_cur = nr_fds_wanted;
> +
> +		if (rl.rlim_max <  nr_fds_wanted)
> +			rl.rlim_max = nr_fds_wanted;

Nit, this could use max().

Reviewed-and-tested-by: Sean Christopherson <seanjc@...gle.com>