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authorDominik Dingel <dingel@linux.vnet.ibm.com>2014-10-31 14:10:41 +0100
committerChristian Borntraeger <borntraeger@de.ibm.com>2015-01-23 13:25:30 +0100
commit8c0a7ce60676caa89c204a1a3b748e065f3d7182 (patch)
tree8f3b3f85b3c99edb88933dd27c210916752aa75e /Documentation/virtual
parentdafd032a15f8f165a7d10e00217d3b74f70a7b0f (diff)
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KVM: s390: Allow userspace to limit guest memory size
With commit c6c956b80bdf ("KVM: s390/mm: support gmap page tables with less than 5 levels") we are able to define a limit for the guest memory size. As we round up the guest size in respect to the levels of page tables we get to guest limits of: 2048 MB, 4096 GB, 8192 TB and 16384 PB. We currently limit the guest size to 16 TB, which means we end up creating a page table structure supporting guest sizes up to 8192 TB. This patch introduces an interface that allows userspace to tune this limit. This may bring performance improvements for small guests. Signed-off-by: Dominik Dingel <dingel@linux.vnet.ibm.com> Acked-by: Cornelia Huck <cornelia.huck@de.ibm.com> Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Diffstat (limited to 'Documentation/virtual')
-rw-r--r--Documentation/virtual/kvm/devices/vm.txt14
1 files changed, 14 insertions, 0 deletions
diff --git a/Documentation/virtual/kvm/devices/vm.txt b/Documentation/virtual/kvm/devices/vm.txt
index d426fc87fe93..c3b17c61b7dd 100644
--- a/Documentation/virtual/kvm/devices/vm.txt
+++ b/Documentation/virtual/kvm/devices/vm.txt
@@ -24,3 +24,17 @@ Returns: 0
Clear the CMMA status for all guest pages, so any pages the guest marked
as unused are again used any may not be reclaimed by the host.
+
+1.3. ATTRIBUTE KVM_S390_VM_MEM_LIMIT_SIZE
+Parameters: in attr->addr the address for the new limit of guest memory
+Returns: -EFAULT if the given address is not accessible
+ -EINVAL if the virtual machine is of type UCONTROL
+ -E2BIG if the given guest memory is to big for that machine
+ -EBUSY if a vcpu is already defined
+ -ENOMEM if not enough memory is available for a new shadow guest mapping
+ 0 otherwise
+
+Allows userspace to query the actual limit and set a new limit for
+the maximum guest memory size. The limit will be rounded up to
+2048 MB, 4096 GB, 8192 TB respectively, as this limit is governed by
+the number of page table levels.
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