linux-kernel - [PATCH 8/9] KVM: s390: Do not report unusabled IDs via KVM_CAP_MAX_VCPU

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Date:   Thu, 23 May 2019 18:43:08 +0200
From:   Thomas Huth <thuth@...hat.com>
To:     Christian Borntraeger <borntraeger@...ibm.com>,
        Janosch Frank <frankja@...ux.ibm.com>, kvm@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Shuah Khan <shuah@...nel.org>,
        David Hildenbrand <david@...hat.com>,
        Cornelia Huck <cohuck@...hat.com>,
        Andrew Jones <drjones@...hat.com>,
        linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
        linux-s390@...r.kernel.org
Subject: [PATCH 8/9] KVM: s390: Do not report unusabled IDs via KVM_CAP_MAX_VCPU_ID

KVM_CAP_MAX_VCPU_ID is currently always reporting KVM_MAX_VCPU_ID on all
architectures. However, on s390x, the amount of usable CPUs is determined
during runtime - it is depending on the features of the machine the code
is running on. Since we are using the vcpu_id as an index into the SCA
structures that are defined by the hardware (see e.g. the sca_add_vcpu()
function), it is not only the amount of CPUs that is limited by the hard-
ware, but also the range of IDs that we can use.
Thus KVM_CAP_MAX_VCPU_ID must be determined during runtime on s390x, too.
So the handling of KVM_CAP_MAX_VCPU_ID has to be moved from the common
code into the architecture specific code, and on s390x we have to return
the same value here as for KVM_CAP_MAX_VCPUS.
This problem has been discovered with the kvm_create_max_vcpus selftest.
With this change applied, the selftest now passes on s390x, too.

Signed-off-by: Thomas Huth <thuth@...hat.com>
---
 arch/mips/kvm/mips.c       | 3 +++
 arch/powerpc/kvm/powerpc.c | 3 +++
 arch/s390/kvm/kvm-s390.c   | 1 +
 arch/x86/kvm/x86.c         | 3 +++
 virt/kvm/arm/arm.c         | 3 +++
 virt/kvm/kvm_main.c        | 2 --
 6 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/arch/mips/kvm/mips.c b/arch/mips/kvm/mips.c
index 6d0517ac18e5..0369f26ab96d 100644
--- a/arch/mips/kvm/mips.c
+++ b/arch/mips/kvm/mips.c
@@ -1122,6 +1122,9 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
 	case KVM_CAP_MAX_VCPUS:
 		r = KVM_MAX_VCPUS;
 		break;
+	case KVM_CAP_MAX_VCPU_ID:
+		r = KVM_MAX_VCPU_ID;
+		break;
 	case KVM_CAP_MIPS_FPU:
 		/* We don't handle systems with inconsistent cpu_has_fpu */
 		r = !!raw_cpu_has_fpu;
diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c
index 3393b166817a..aa3a678711be 100644
--- a/arch/powerpc/kvm/powerpc.c
+++ b/arch/powerpc/kvm/powerpc.c
@@ -657,6 +657,9 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
 	case KVM_CAP_MAX_VCPUS:
 		r = KVM_MAX_VCPUS;
 		break;
+	case KVM_CAP_MAX_VCPU_ID:
+		r = KVM_MAX_VCPU_ID;
+		break;
 #ifdef CONFIG_PPC_BOOK3S_64
 	case KVM_CAP_PPC_GET_SMMU_INFO:
 		r = 1;
diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index 8d6d75db8de6..871d2e99b156 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -539,6 +539,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
 		break;
 	case KVM_CAP_NR_VCPUS:
 	case KVM_CAP_MAX_VCPUS:
+	case KVM_CAP_MAX_VCPU_ID:
 		r = KVM_S390_BSCA_CPU_SLOTS;
 		if (!kvm_s390_use_sca_entries())
 			r = KVM_MAX_VCPUS;
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 536b78c4af6e..09a07d6a154e 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3122,6 +3122,9 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
 	case KVM_CAP_MAX_VCPUS:
 		r = KVM_MAX_VCPUS;
 		break;
+	case KVM_CAP_MAX_VCPU_ID:
+		r = KVM_MAX_VCPU_ID;
+		break;
 	case KVM_CAP_PV_MMU:	/* obsolete */
 		r = 0;
 		break;
diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c
index 90cedebaeb94..7eeebe5e9da2 100644
--- a/virt/kvm/arm/arm.c
+++ b/virt/kvm/arm/arm.c
@@ -224,6 +224,9 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
 	case KVM_CAP_MAX_VCPUS:
 		r = KVM_MAX_VCPUS;
 		break;
+	case KVM_CAP_MAX_VCPU_ID:
+		r = KVM_MAX_VCPU_ID;
+		break;
 	case KVM_CAP_MSI_DEVID:
 		if (!kvm)
 			r = -EINVAL;
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index f0d13d9d125d..c09259dd6286 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -3146,8 +3146,6 @@ static long kvm_vm_ioctl_check_extension_generic(struct kvm *kvm, long arg)
 	case KVM_CAP_MULTI_ADDRESS_SPACE:
 		return KVM_ADDRESS_SPACE_NUM;
 #endif
-	case KVM_CAP_MAX_VCPU_ID:
-		return KVM_MAX_VCPU_ID;
 	case KVM_CAP_NR_MEMSLOTS:
 		return KVM_USER_MEM_SLOTS;
 	default:
-- 
2.21.0