kvm tools: Update max VCPU limit

Use the newly introduced KVM_CAP_MAX_VCPUS to determine max VCPU count
the kernel side supports.

Using more VCPUs than the recommended limit will issue a warning, using more
than the absolute maximum will limit it down to the absolute maximum.

Note this patch contains a hack to define KVM_CAP_MAX_VCPUS and should be
removed when the kernel patch is merged with mainline.

Signed-off-by: Sasha Levin <levinsasha928@gmail.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>

diff --git a/tools/kvm/builtin-run.c b/tools/kvm/builtin-run.c
index af2e089c699b4251ee2c186ad0f5f43f634173d2..3345bf80e80f62765baa52af89c3bebe52ec6bec 100644 (file)
--- a/tools/kvm/builtin-run.c
+++ b/tools/kvm/builtin-run.c
@@ -478,7 +478,7 @@ int kvm_cmd_run(int argc, const char **argv, const char *prefix)
        struct framebuffer *fb = NULL;
        unsigned int nr_online_cpus;
        int exit_code = 0;
-       int max_cpus;
+       int max_cpus, recommended_cpus;
        char *hi;
        int i;
        void *ret;
@@ -578,10 +578,14 @@ int kvm_cmd_run(int argc, const char **argv, const char *prefix)
        ioeventfd__init();
 
        max_cpus = kvm__max_cpus(kvm);
+       recommended_cpus = kvm__recommended_cpus(kvm);
 
        if (nrcpus > max_cpus) {
                printf("  # Limit the number of CPUs to %d\n", max_cpus);
                kvm->nrcpus     = max_cpus;
+       } else if (nrcpus > recommended_cpus) {
+               printf("  # Warning: The maximum recommended amount of VCPUs"
+                       " is %d\n", recommended_cpus);
        }
 
        kvm->nrcpus = nrcpus;

diff --git a/tools/kvm/include/kvm/kvm.h b/tools/kvm/include/kvm/kvm.h
index 8792af21f7dae19f9a3a9510bd2601702321a64d..eeb55b6f32265ae04710a9bc64db87efe15c6bd9 100644 (file)
--- a/tools/kvm/include/kvm/kvm.h
+++ b/tools/kvm/include/kvm/kvm.h
@@ -51,6 +51,7 @@ struct kvm {
 };
 
 struct kvm *kvm__init(const char *kvm_dev, u64 ram_size, const char *name);
+int kvm__recommended_cpus(struct kvm *kvm);
 int kvm__max_cpus(struct kvm *kvm);
 void kvm__init_ram(struct kvm *kvm);
 void kvm__delete(struct kvm *kvm);

diff --git a/tools/kvm/kvm.c b/tools/kvm/kvm.c
index 248eaf4b9e5ec741abd43248c32d645f7c64c24d..107a9223febe7a9d011ae2673bd0452eb4d3b2d7 100644 (file)
--- a/tools/kvm/kvm.c
+++ b/tools/kvm/kvm.c
@@ -304,17 +304,36 @@ void kvm__init_ram(struct kvm *kvm)
        }
 }
 
-int kvm__max_cpus(struct kvm *kvm)
+int kvm__recommended_cpus(struct kvm *kvm)
 {
        int ret;
 
        ret = ioctl(kvm->sys_fd, KVM_CHECK_EXTENSION, KVM_CAP_NR_VCPUS);
-       if (ret < 0)
+       if (ret <= 0)
                die_perror("KVM_CAP_NR_VCPUS");
 
        return ret;
 }
 
+/*
+ * The following hack should be removed once 'x86: Raise the hard
+ * VCPU count limit' makes it's way into the mainline.
+ */
+#ifndef KVM_CAP_MAX_VCPUS
+#define KVM_CAP_MAX_VCPUS 66
+#endif
+
+int kvm__max_cpus(struct kvm *kvm)
+{
+       int ret;
+
+       ret = ioctl(kvm->sys_fd, KVM_CHECK_EXTENSION, KVM_CAP_MAX_VCPUS);
+       if (ret <= 0)
+               ret = kvm__recommended_cpus(kvm);
+
+       return ret;
+}
+
 struct kvm *kvm__init(const char *kvm_dev, u64 ram_size, const char *name)
 {
        struct kvm_pit_config pit_config = { .flags = 0, };