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Commit 40ebdb8e authored by Janosch Frank's avatar Janosch Frank
Browse files

KVM: s390: Make huge pages unavailable in ucontrol VMs 



We currently do not notify all gmaps when using gmap_pmdp_xchg(), due
to locking constraints. This makes ucontrol VMs, which is the only VM
type that creates multiple gmaps, incompatible with huge pages. Also
we would need to hold the guest_table_lock of all gmaps that have this
vmaddr maped to synchronize access to the pmd.

ucontrol VMs are rather exotic and creating a new locking concept is
no easy task. Hence we return EINVAL when trying to active
KVM_CAP_S390_HPAGE_1M and report it as being not available when
checking for it.

Fixes: a4499382 ("KVM: s390: Add huge page enablement control")
Signed-off-by: default avatarJanosch Frank <frankja@linux.ibm.com>
Reviewed-by: default avatarDavid Hildenbrand <david@redhat.com>
Reviewed-by: default avatarClaudio Imbrenda <imbrenda@linux.ibm.com>
Message-Id: <20180801112508.138159-1-frankja@linux.ibm.com>
Signed-off-by: default avatarJanosch Frank <frankja@linux.ibm.com>
parent 1843abd0

Documentation/virtual/kvm/api.txt

+2 −1
Original line number Diff line number Diff line
@@ -4510,7 +4510,8 @@ Do not enable KVM_FEATURE_PV_UNHALT if you disable HLT exits. 
Architectures: s390

Parameters: none

Returns: 0 on success, -EINVAL if hpage module parameter was not set

	 or cmma is enabled

	 or cmma is enabled, or the VM has the KVM_VM_S390_UCONTROL

	 flag set



With this capability the KVM support for memory backing with 1m pages

through hugetlbfs can be enabled for a VM. After the capability is

arch/s390/kvm/kvm-s390.c

+2 −2
Original line number Diff line number Diff line
@@ -481,7 +481,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext) 
		break;

	case KVM_CAP_S390_HPAGE_1M:

		r = 0;

		if (hpage)

		if (hpage && !kvm_is_ucontrol(kvm))

			r = 1;

		break;

	case KVM_CAP_S390_MEM_OP:
@@ -691,7 +691,7 @@ static int kvm_vm_ioctl_enable_cap(struct kvm *kvm, struct kvm_enable_cap *cap) 
		mutex_lock(&kvm->lock);

		if (kvm->created_vcpus)

			r = -EBUSY;

		else if (!hpage || kvm->arch.use_cmma)

		else if (!hpage || kvm->arch.use_cmma || kvm_is_ucontrol(kvm))

			r = -EINVAL;

		else {

			r = 0;