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

 Parameters: vcpu id (apic id on x86)
 Returns: vcpu fd on success, -1 on error
-This API adds a vcpu to a virtual machine.  The vcpu id is a small integer
+This API adds a vcpu to a virtual machine. No more than max_vcpus may be added.
-in the range [0, max_vcpus).
+The vcpu id is an integer in the range [0, max_vcpu_id).
 The recommended max_vcpus value can be retrieved using the KVM_CAP_NR_VCPUS of
 the KVM_CHECK_EXTENSION ioctl() at run-time.
 If the KVM_CAP_MAX_VCPUS does not exist, you should assume that max_vcpus is
 same as the value returned from KVM_CAP_NR_VCPUS.
+The maximum possible value for max_vcpu_id can be retrieved using the
+KVM_CAP_MAX_VCPU_ID of the KVM_CHECK_EXTENSION ioctl() at run-time.
+If the KVM_CAP_MAX_VCPU_ID does not exist, you should assume that max_vcpu_id
+is the same as the value returned from KVM_CAP_MAX_VCPUS.
 On powerpc using book3s_hv mode, the vcpus are mapped onto virtual
 threads in one or more virtual CPU cores.  (This is because the
 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	#define KVM_MAX_VCORES NR_CPUS	40	#define KVM_MAX_VCORES NR_CPUS
41	#define KVM_USER_MEM_SLOTS 512	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	#ifdef CONFIG_KVM_MMIO	46	#ifdef CONFIG_KVM_MMIO
44	#define KVM_COALESCED_MMIO_PAGE_OFFSET 1	47	#define KVM_COALESCED_MMIO_PAGE_OFFSET 1
45	#endif	48	#endif

include/linux/kvm_host.h+4−0

@@ -35,6 +35,10 @@ · 34 unmodified lines
35		35
36	#include <asm/kvm_host.h>	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	* The bit 16 ~ bit 31 of kvm_memory_region::flags are internally used	43	* The bit 16 ~ bit 31 of kvm_memory_region::flags are internally used
40	* in kvm, other bits are visible for userspace which are defined in	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	#define KVM_CAP_SPAPR_TCE_64 125	865	#define KVM_CAP_SPAPR_TCE_64 125
866	#define KVM_CAP_ARM_PMU_V3 126	866	#define KVM_CAP_ARM_PMU_V3 126
867	#define KVM_CAP_VCPU_ATTRIBUTES 127	867	#define KVM_CAP_VCPU_ATTRIBUTES 127
		868	#define KVM_CAP_MAX_VCPU_ID 128
868		869
869	#ifdef KVM_CAP_IRQ_ROUTING	870	#ifdef KVM_CAP_IRQ_ROUTING
870		871

virt/kvm/kvm_main.c+3−1

 	int r;
 	struct kvm_vcpu *vcpu;
-	if (id >= KVM_MAX_VCPUS)
+	if (id >= KVM_MAX_VCPU_ID)
 		return -EINVAL;
 	vcpu = kvm_arch_vcpu_create(kvm, id);
 	case KVM_CAP_MULTI_ADDRESS_SPACE:
 		return KVM_ADDRESS_SPACE_NUM;
 #endif
+	case KVM_CAP_MAX_VCPU_ID:
+		return KVM_MAX_VCPU_ID;
 	default:
 		break;
 	}