kvm: introduce KVM_MAX_VCPU_ID

The KVM_MAX_VCPUS define provides the maximum number of vCPUs per guest, and also the upper limit for vCPU ids. This is okay for all archs except PowerPC which can have higher ids, depending on the cpu/core/thread topology. In the worst case (single threaded guest, host with 8 threads per core), it limits the maximum number of vCPUS to KVM_MAX_VCPUS / 8. This patch separates the vCPU numbering from the total number of vCPUs, with the introduction of KVM_MAX_VCPU_ID, as the maximal valid value for vCPU ids plus one. The corresponding KVM_CAP_MAX_VCPU_ID allows userspace to validate vCPU ids before passing them to KVM_CREATE_VCPU. This patch only implements KVM_MAX_VCPU_ID with a specific value for PowerPC. Other archs continue to return KVM_MAX_VCPUS instead.

Greg Kurz committed 10 years ago

Commit 0b1b1df1 parent 9b9e3fc5 files · +19 −3Browse files

Unified · Split

5 files

Documentation/virtual/kvm/api.txt +8 −2
arch/powerpc/include/asm/kvm_host.h +3 −0
include/linux/kvm_host.h +4 −0
include/uapi/linux/kvm.h +1 −0
virt/kvm/kvm_main.c +3 −1

Documentation/virtual/kvm/api.txt+8−2

@@ -199,8 +199,8 @@ Type: vm ioctl · 198 unmodified lines
199	199	Parameters: vcpu id (apic id on x86)
200	200	Returns: vcpu fd on success, -1 on error
201	201
202		−This API adds a vcpu to a virtual machine. The vcpu id is a small integer
203		−in the range [0, max_vcpus).
	202	+This API adds a vcpu to a virtual machine. No more than max_vcpus may be added.
	203	+The vcpu id is an integer in the range [0, max_vcpu_id).
204	204
205	205	The recommended max_vcpus value can be retrieved using the KVM_CAP_NR_VCPUS of
206	206	the KVM_CHECK_EXTENSION ioctl() at run-time.
@@ -212,6 +212,12 @@ cpus max. · 5 unmodified lines
212	212	If the KVM_CAP_MAX_VCPUS does not exist, you should assume that max_vcpus is
213	213	same as the value returned from KVM_CAP_NR_VCPUS.
214	214
	215	+The maximum possible value for max_vcpu_id can be retrieved using the
	216	+KVM_CAP_MAX_VCPU_ID of the KVM_CHECK_EXTENSION ioctl() at run-time.
	217	+
	218	+If the KVM_CAP_MAX_VCPU_ID does not exist, you should assume that max_vcpu_id
	219	+is the same as the value returned from KVM_CAP_MAX_VCPUS.
	220	+
215	221	On powerpc using book3s_hv mode, the vcpus are mapped onto virtual
216	222	threads in one or more virtual CPU cores. (This is because the
217	223	hardware requires all the hardware threads in a CPU core to be in the

arch/powerpc/include/asm/kvm_host.h+3−0

@@ -40,6 +40,9 @@ · 39 unmodified lines
40	40	#define KVM_MAX_VCORES NR_CPUS
41	41	#define KVM_USER_MEM_SLOTS 512
42	42
	43	+#include <asm/cputhreads.h>
	44	+#define KVM_MAX_VCPU_ID (threads_per_subcore * KVM_MAX_VCORES)
	45	+
43	46	#ifdef CONFIG_KVM_MMIO
44	47	#define KVM_COALESCED_MMIO_PAGE_OFFSET 1
45	48	#endif

include/linux/kvm_host.h+4−0

@@ -35,6 +35,10 @@ · 34 unmodified lines
35	35
36	36	#include <asm/kvm_host.h>
37	37
	38	+#ifndef KVM_MAX_VCPU_ID
	39	+#define KVM_MAX_VCPU_ID KVM_MAX_VCPUS
	40	+#endif
	41	+
38	42	/*
39	43	* The bit 16 ~ bit 31 of kvm_memory_region::flags are internally used
40	44	* in kvm, other bits are visible for userspace which are defined in

include/uapi/linux/kvm.h+1−0

@@ -865,6 +865,7 @@ struct kvm_ppc_smmu_info { · 864 unmodified lines
865	865	#define KVM_CAP_SPAPR_TCE_64 125
866	866	#define KVM_CAP_ARM_PMU_V3 126
867	867	#define KVM_CAP_VCPU_ATTRIBUTES 127
	868	+#define KVM_CAP_MAX_VCPU_ID 128
868	869
869	870	#ifdef KVM_CAP_IRQ_ROUTING
870	871

virt/kvm/kvm_main.c+3−1

@@ -2272,7 +2272,7 @@ static int kvm_vm_ioctl_create_vcpu(struct kvm *kvm, u32 id) · 2271 unmodified lines
2272	2272	int r;
2273	2273	struct kvm_vcpu *vcpu;
2274	2274
2275		− if (id >= KVM_MAX_VCPUS)
	2275	+ if (id >= KVM_MAX_VCPU_ID)
2276	2276	return -EINVAL;
2277	2277
2278	2278	vcpu = kvm_arch_vcpu_create(kvm, id);
@@ -2746,6 +2746,8 @@ static long kvm_vm_ioctl_check_extension_generic(struct kvm *kvm, long arg) · 467 unmodified lines
2746	2746	case KVM_CAP_MULTI_ADDRESS_SPACE:
2747	2747	return KVM_ADDRESS_SPACE_NUM;
2748	2748	#endif
	2749	+ case KVM_CAP_MAX_VCPU_ID:
	2750	+ return KVM_MAX_VCPU_ID;
2749	2751	default:
2750	2752	break;
2751	2753	}