[PATCH] kvm tools: Limit CPU count by KVM_CAP_NR_VCPUS

[Pekka Enberg]

This patch limits the number of CPUs to KVM_CAP_NR_VCPUS when user specifies
more CPUs with the "--cpus=N" command line option than what the in-kernel KVM
is able to handle.

Cc: Asias He <asias.he...@gmail.com>
Cc: Cyrill Gorcunov <gorcu...@gmail.com>
Cc: Ingo Molnar <mi...@elte.hu>
Cc: Prasad Joshi <prasadjoshi...@gmail.com>
Cc: Sasha Levin <levinsasha...@gmail.com>
Signed-off-by: Pekka Enberg <penb...@kernel.org>
---
 tools/kvm/include/kvm/kvm.h |    1 +
 tools/kvm/kvm-run.c         |   10 +++++++++-
 tools/kvm/kvm.c             |   11 +++++++++++
 3 files changed, 21 insertions(+), 1 deletions(-)

diff --git a/tools/kvm/include/kvm/kvm.h b/tools/kvm/include/kvm/kvm.h
index f697579..3dab78d 100644
--- a/tools/kvm/include/kvm/kvm.h
+++ b/tools/kvm/include/kvm/kvm.h
@@ -29,6 +29,7 @@ struct kvm {
 };
 
 struct kvm *kvm__init(const char *kvm_dev, unsigned long ram_size);
+int kvm__max_cpus(struct kvm *self);
 void kvm__init_ram(struct kvm *self);
 void kvm__delete(struct kvm *self);
 bool kvm__load_kernel(struct kvm *kvm, const char *kernel_filename,
diff --git a/tools/kvm/kvm-run.c b/tools/kvm/kvm-run.c
index 2504ab0..ec1e462 100644
--- a/tools/kvm/kvm-run.c
+++ b/tools/kvm/kvm-run.c
@@ -311,11 +311,12 @@ static char *host_image(char *cmd_line, size_t size)
 int kvm_cmd_run(int argc, const char **argv, const char *prefix)
 {
        static char real_cmdline[2048];
+       unsigned int nr_online_cpus;
+       int max_cpus;
        int exit_code = 0;
        int i;
        struct virtio_net_parameters net_params;
        char *hi;
-       unsigned int nr_online_cpus;
 
        signal(SIGALRM, handle_sigalrm);
        signal(SIGQUIT, handle_sigquit);
@@ -383,6 +384,13 @@ int kvm_cmd_run(int argc, const char **argv, const char 
*prefix)
 
        kvm = kvm__init(kvm_dev, ram_size);
 
+       max_cpus = kvm__max_cpus(kvm);
+
+       if (nrcpus > max_cpus) {
+               printf("  # Limit the number of CPUs to %d\n", max_cpus);
+               kvm->nrcpus     = max_cpus;
+       }
+
        kvm->nrcpus = nrcpus;
 
        memset(real_cmdline, 0, sizeof(real_cmdline));
diff --git a/tools/kvm/kvm.c b/tools/kvm/kvm.c
index b3adb6b..65793f2 100644
--- a/tools/kvm/kvm.c
+++ b/tools/kvm/kvm.c
@@ -170,6 +170,17 @@ void kvm__init_ram(struct kvm *self)
                die_perror("KVM_SET_USER_MEMORY_REGION ioctl");
 }
 
+int kvm__max_cpus(struct kvm *self)
+{
+       int ret;
+
+       ret = ioctl(self->sys_fd, KVM_CHECK_EXTENSION, KVM_CAP_NR_VCPUS);
+       if (ret < 0)
+               die_perror("KVM_CAP_NR_VCPUS");
+
+       return ret;
+}
+
 struct kvm *kvm__init(const char *kvm_dev, unsigned long ram_size)
 {
        struct kvm_pit_config pit_config = { .flags = 0, };
-- 
1.7.0.4

--
To unsubscribe from this list: send the line "unsubscribe kvm" in
the body of a message to majord...@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html