linux-kernel - Re: [PATCH MANUALSEL 5.10 3/4] KVM: selftests: Make sure kvm_create_max_vcpus test won't hit RLIMIT

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Date:   Mon, 13 Dec 2021 15:22:01 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sasha Levin <sashal@...nel.org>, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org
Cc:     Vitaly Kuznetsov <vkuznets@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>, shuah@...nel.org,
        kvm@...r.kernel.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH MANUALSEL 5.10 3/4] KVM: selftests: Make sure
 kvm_create_max_vcpus test won't hit RLIMIT_NOFILE

On 12/13/21 15:20, Sasha Levin wrote:
> From: Vitaly Kuznetsov <vkuznets@...hat.com>
> 
> [ Upstream commit 908fa88e420f30dde6d80f092795a18ec72ca6d3 ]
> 
> 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>
> Message-Id: <20211123135953.667434-1-vkuznets@...hat.com>
> [Skip the test if the hard limit can be raised. - Paolo]
> Reviewed-by: Sean Christopherson <seanjc@...gle.com>
> Tested-by: Sean Christopherson <seanjc@...gle.com>
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> Signed-off-by: Sasha Levin <sashal@...nel.org>
> ---
>   .../selftests/kvm/kvm_create_max_vcpus.c      | 30 +++++++++++++++++++
>   1 file changed, 30 insertions(+)
> 
> diff --git a/tools/testing/selftests/kvm/kvm_create_max_vcpus.c b/tools/testing/selftests/kvm/kvm_create_max_vcpus.c
> index 0299cd81b8ba2..aa3795cd7bd3d 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 +41,39 @@ 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) {
> +			int old_rlim_max = rl.rlim_max;
> +			rl.rlim_max = nr_fds_wanted;
> +
> +			int r = setrlimit(RLIMIT_NOFILE, &rl);
> +			if (r < 0) {
> +				printf("RLIMIT_NOFILE hard limit is too low (%d, wanted %d)\n",
> +				       old_rlim_max, nr_fds_wanted);
> +				exit(KSFT_SKIP);
> +			}
> +		} else {
> +			TEST_ASSERT(!setrlimit(RLIMIT_NOFILE, &rl), "setrlimit() failed!");
> +		}
> +	}
> +
>   	/*
>   	 * 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
> 

Acked-by: Paolo Bonzini <pbonzini@...hat.com>