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

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Date:   Mon, 22 Nov 2021 18:19:20 +0100
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>, linux-kernel@...r.kernel.org
Subject: [PATCH] KVM: selftests: Make sure kvm_create_max_vcpus test won't hit RLIMIT_NOFILE

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>
---
 .../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
+
 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);
+	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);
+
+	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