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| author |   Janosch Frank <frankja@linux.ibm.com> | 2018-07-13 11:28:31 +0100 |
|---|---|---|
| committer | Janosch Frank <frankja@linux.ibm.com> | 2018-07-30 23:13:38 +0200 |
| commit | a449938297e55e7e8958f8b48583f7d342da1930 (patch) | |
| tree | 89157c9c2d20a171c5685f3f7b7c1fdad72122cd /Documentation/virtual | |
| parent | s390/mm: Add huge page gmap linking support (diff) | |
| download | linux-dev-a449938297e55e7e8958f8b48583f7d342da1930.tar.xz linux-dev-a449938297e55e7e8958f8b48583f7d342da1930.zip | |
KVM: s390: Add huge page enablement control
General KVM huge page support on s390 has to be enabled via the
kvm.hpage module parameter. Either nested or hpage can be enabled, as
we currently do not support vSIE for huge backed guests. Once the vSIE
support is added we will either drop the parameter or enable it as
default.
For a guest the feature has to be enabled through the new
KVM_CAP_S390_HPAGE_1M capability and the hpage module
parameter. Enabling it means that cmm can't be enabled for the vm and
disables pfmf and storage key interpretation.
This is due to the fact that in some cases, in upcoming patches, we
have to split huge pages in the guest mapping to be able to set more
granular memory protection on 4k pages. These split pages have fake
page tables that are not visible to the Linux memory management which
subsequently will not manage its PGSTEs, while the SIE will. Disabling
these features lets us manage PGSTE data in a consistent matter and
solve that problem.
Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Diffstat (limited to 'Documentation/virtual')
| -rw-r--r-- | Documentation/virtual/kvm/api.txt | 16 |
1 files changed, 16 insertions, 0 deletions
diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt index d10944e619d3..cb8db4f9d097 100644 --- a/Documentation/virtual/kvm/api.txt +++ b/Documentation/virtual/kvm/api.txt @@ -4391,6 +4391,22 @@ all such vmexits. Do not enable KVM_FEATURE_PV_UNHALT if you disable HLT exits. +7.14 KVM_CAP_S390_HPAGE_1M + +Architectures: s390 +Parameters: none +Returns: 0 on success, -EINVAL if hpage module parameter was not set + or cmma is enabled + +With this capability the KVM support for memory backing with 1m pages +through hugetlbfs can be enabled for a VM. After the capability is +enabled, cmma can't be enabled anymore and pfmfi and the storage key +interpretation are disabled. If cmma has already been enabled or the +hpage module parameter is not set to 1, -EINVAL is returned. + +While it is generally possible to create a huge page backed VM without +this capability, the VM will not be able to run. + 8. Other capabilities. ---------------------- |