diff options
| author | Ben Gardon | 2022-06-13 21:25:21 +0000 |
|---|---|---|
| committer | Paolo Bonzini | 2022-06-24 04:51:49 -0400 |
| commit | 084cc29f8bbb034cf30a7ee07a816c115e0c28df (patch) | |
| tree | 8324b06915b515128d5490888e78de420e18ae20 /Documentation/virt/kvm | |
| parent | 1c4dc57328bf218e999951824dce75c6125c4f3c (diff) | |
KVM: x86/MMU: Allow NX huge pages to be disabled on a per-vm basis
In some cases, the NX hugepage mitigation for iTLB multihit is not
needed for all guests on a host. Allow disabling the mitigation on a
per-VM basis to avoid the performance hit of NX hugepages on trusted
workloads.
In order to disable NX hugepages on a VM, ensure that the userspace
actor has permission to reboot the system. Since disabling NX hugepages
would allow a guest to crash the system, it is similar to reboot
permissions.
Ideally, KVM would require userspace to prove it has access to KVM's
nx_huge_pages module param, e.g. so that userspace can opt out without
needing full reboot permissions. But getting access to the module param
file info is difficult because it is buried in layers of sysfs and module
glue. Requiring CAP_SYS_BOOT is sufficient for all known use cases.
Suggested-by: Jim Mattson <jmattson@google.com>
Reviewed-by: David Matlack <dmatlack@google.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Ben Gardon <bgardon@google.com>
Message-Id: <20220613212523.3436117-9-bgardon@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'Documentation/virt/kvm')
| -rw-r--r-- | Documentation/virt/kvm/api.rst | 16 |
1 files changed, 16 insertions, 0 deletions
diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst index 320cb04f7bd9..bafaeedd455c 100644 --- a/Documentation/virt/kvm/api.rst +++ b/Documentation/virt/kvm/api.rst @@ -8206,6 +8206,22 @@ PV guests. The `KVM_PV_DUMP` command is available for the dump related UV data. Also the vcpu ioctl `KVM_S390_PV_CPU_COMMAND` is available and supports the `KVM_PV_DUMP_CPU` subcommand. +8.38 KVM_CAP_VM_DISABLE_NX_HUGE_PAGES +--------------------------- + +:Capability KVM_CAP_VM_DISABLE_NX_HUGE_PAGES +:Architectures: x86 +:Type: vm +:Parameters: arg[0] must be 0. +:Returns 0 on success, -EPERM if the userspace process does not + have CAP_SYS_BOOT, -EINVAL if args[0] is not 0 or any vCPUs have been + created. + +This capability disables the NX huge pages mitigation for iTLB MULTIHIT. + +The capability has no effect if the nx_huge_pages module parameter is not set. + +This capability may only be set before any vCPUs are created. 9. Known KVM API problems ========================= |