The detection of the maximum number of cpus used incorrect ioctl argument value. This flaw caused that on kvm hosts this returns always "160" as the maximum. This is just a recommended maximum value. The real value is higher than that. This patch tweaks the detection function to behave as described by the kernel docs: https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documen... --- src/qemu/qemu_driver.c | 29 +++++++++++++++++++---------- 1 file changed, 19 insertions(+), 10 deletions(-) diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c index f4bbd74..7ca3e4c 100644 --- a/src/qemu/qemu_driver.c +++ b/src/qemu/qemu_driver.c @@ -1103,23 +1103,32 @@ static int qemuIsAlive(virConnectPtr conn ATTRIBUTE_UNUSED) } -static int kvmGetMaxVCPUs(void) { - int maxvcpus = 1; - - int r, fd; +static int +kvmGetMaxVCPUs(void) { + int fd; + int ret; - fd = open(KVM_DEVICE, O_RDONLY); - if (fd < 0) { + if ((fd = open(KVM_DEVICE, O_RDONLY)) < 0) { virReportSystemError(errno, _("Unable to open %s"), KVM_DEVICE); return -1; } - r = ioctl(fd, KVM_CHECK_EXTENSION, KVM_CAP_NR_VCPUS); - if (r > 0) - maxvcpus = r; + /* at first try KVM_CAP_MAX_VCPUS to determine the maximum count */ + if ((ret = ioctl(fd, KVM_CHECK_EXTENSION, KVM_CAP_MAX_VCPUS)) > 0) + goto cleanup; + + /* as a fallback get KVM_CAP_NR_VCPUS (the recommended maximum number of + * vcpus). Note that on most machines this is set to 160. */ + if ((ret = ioctl(fd, KVM_CHECK_EXTENSION, KVM_CAP_NR_VCPUS)) > 0) + goto cleanup; + + /* if KVM_CAP_NR_VCPUS doesn't exist either, kernel documentation states + * that 4 should be used as the maximum number of cpus */ + ret = 4; +cleanup: VIR_FORCE_CLOSE(fd); - return maxvcpus; + return ret; } -- 1.8.1.5