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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: Janosch Frank <frankja@linux.ibm.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Message-Id: <20180801112508.138159-1-frankja@linux.ibm.com>
Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
This commit is contained in:
Janosch Frank 2018-08-01 11:48:28 +01:00
parent 1843abd032
commit 40ebdb8e59
2 changed files with 4 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

3
Documentation/virtual/kvm/api.txt
View File

@ -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

4
arch/s390/kvm/kvm-s390.c
View File

@ -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;