Today the maximum number of vcpus of a kvm guest is set via a #define in a header file. In order to support higher vcpu numbers for guests without generally increasing the memory consumption of guests on the host especially on very large systems add a boot parameter for specifying the number of allowed vcpus for guests. The default will still be the current setting of 288. The value 0 has the special meaning to limit the number of possible vcpus to the number of possible cpus of the host. Signed-off-by: Juergen Gross <jgross@xxxxxxxx> --- Documentation/admin-guide/kernel-parameters.txt | 10 ++++++++++ arch/x86/include/asm/kvm_host.h | 5 ++++- arch/x86/kvm/x86.c | 7 +++++++ 3 files changed, 21 insertions(+), 1 deletion(-) diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index 99bfa53a2bbd..8eb856396ffa 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -2373,6 +2373,16 @@ guest can't have more vcpus than the set value + 1. Default: 1023 + kvm.max_vcpus= [KVM,X86] Set the maximum allowed numbers of vcpus per + guest. The special value 0 sets the limit to the number + of physical cpus possible on the host (including not + yet hotplugged cpus). Higher values will result in + slightly higher memory consumption per guest. Depending + on the value and the virtual topology the maximum + allowed vcpu-id might need to be raised, too (see + kvm.max_vcpu_id parameter). + Default: 288 + l1tf= [X86] Control mitigation of the L1TF vulnerability on affected CPUs diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h index 39cbc4b6bffb..65ae82a5d444 100644 --- a/arch/x86/include/asm/kvm_host.h +++ b/arch/x86/include/asm/kvm_host.h @@ -37,7 +37,8 @@ #define __KVM_HAVE_ARCH_VCPU_DEBUGFS -#define KVM_MAX_VCPUS 288 +#define KVM_DEFAULT_MAX_VCPUS 288 +#define KVM_MAX_VCPUS max_vcpus #define KVM_SOFT_MAX_VCPUS 240 #define KVM_DEFAULT_MAX_VCPU_ID 1023 #define KVM_MAX_VCPU_ID max_vcpu_id @@ -1509,6 +1510,8 @@ extern u64 kvm_max_tsc_scaling_ratio; extern u64 kvm_default_tsc_scaling_ratio; /* bus lock detection supported? */ extern bool kvm_has_bus_lock_exit; +/* maximum number of vcpus per guest */ +extern unsigned int max_vcpus; /* maximum vcpu-id */ extern unsigned int max_vcpu_id; /* per cpu vcpu bitmasks (disable preemption during usage) */ diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index a9b0bb2221ea..888c4507504d 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -177,6 +177,10 @@ module_param(force_emulation_prefix, bool, S_IRUGO); int __read_mostly pi_inject_timer = -1; module_param(pi_inject_timer, bint, S_IRUGO | S_IWUSR); +unsigned int __read_mostly max_vcpus = KVM_DEFAULT_MAX_VCPUS; +module_param(max_vcpus, uint, S_IRUGO); +EXPORT_SYMBOL_GPL(max_vcpus); + unsigned int __read_mostly max_vcpu_id = KVM_DEFAULT_MAX_VCPU_ID; module_param(max_vcpu_id, uint, S_IRUGO); @@ -10648,6 +10652,9 @@ int kvm_arch_hardware_setup(void *opaque) if (boot_cpu_has(X86_FEATURE_XSAVES)) rdmsrl(MSR_IA32_XSS, host_xss); + if (max_vcpus == 0) + max_vcpus = num_possible_cpus(); + kvm_pcpu_vcpu_mask = __alloc_percpu(KVM_VCPU_MASK_SZ, sizeof(unsigned long)); kvm_hv_vp_bitmap = __alloc_percpu(KVM_HV_VPMAP_SZ, sizeof(u64)); -- 2.26.2
