path: root/Documentation/virtual
diff options
authorPaul Mackerras <paulus@samba.org>2014-06-02 11:02:59 +1000
committerAlexander Graf <agraf@suse.de>2014-07-28 15:22:17 +0200
commit699a0ea0823d32030b0666b28ff8633960f7ffa7 (patch)
treefdfa3e767593f47b66a08313e97cd0fe35b12300 /Documentation/virtual
parent1f0eeb7e1a88f46afa0f435cf7c34b0c84cf2394 (diff)
KVM: PPC: Book3S: Controls for in-kernel sPAPR hypercall handling
This provides a way for userspace controls which sPAPR hcalls get handled in the kernel. Each hcall can be individually enabled or disabled for in-kernel handling, except for H_RTAS. The exception for H_RTAS is because userspace can already control whether individual RTAS functions are handled in-kernel or not via the KVM_PPC_RTAS_DEFINE_TOKEN ioctl, and because the numeric value for H_RTAS is out of the normal sequence of hcall numbers. Hcalls are enabled or disabled using the KVM_ENABLE_CAP ioctl for the KVM_CAP_PPC_ENABLE_HCALL capability on the file descriptor for the VM. The args field of the struct kvm_enable_cap specifies the hcall number in args[0] and the enable/disable flag in args[1]; 0 means disable in-kernel handling (so that the hcall will always cause an exit to userspace) and 1 means enable. Enabling or disabling in-kernel handling of an hcall is effective across the whole VM. The ability for KVM_ENABLE_CAP to be used on a VM file descriptor on PowerPC is new, added by this commit. The KVM_CAP_ENABLE_CAP_VM capability advertises that this ability exists. When a VM is created, an initial set of hcalls are enabled for in-kernel handling. The set that is enabled is the set that have an in-kernel implementation at this point. Any new hcall implementations from this point onwards should not be added to the default set without a good reason. No distinction is made between real-mode and virtual-mode hcall implementations; the one setting controls them both. Signed-off-by: Paul Mackerras <paulus@samba.org> Signed-off-by: Alexander Graf <agraf@suse.de>
Diffstat (limited to 'Documentation/virtual')
1 files changed, 39 insertions, 2 deletions
diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
index 0fe36497642c..5c54d196f4c8 100644
--- a/Documentation/virtual/kvm/api.txt
+++ b/Documentation/virtual/kvm/api.txt
@@ -2863,8 +2863,8 @@ The fields in each entry are defined as follows:
this function/index combination
-6. Capabilities that can be enabled
+6. Capabilities that can be enabled on vCPUs
There are certain capabilities that change the behavior of the virtual CPU when
enabled. To enable them, please see section 4.37. Below you can find a list of
@@ -3002,3 +3002,40 @@ Parameters: args[0] is the XICS device fd
args[1] is the XICS CPU number (server ID) for this vcpu
This capability connects the vcpu to an in-kernel XICS device.
+7. Capabilities that can be enabled on VMs
+There are certain capabilities that change the behavior of the virtual
+machine when enabled. To enable them, please see section 4.37. Below
+you can find a list of capabilities and what their effect on the VM
+is when enabling them.
+The following information is provided along with the description:
+ Architectures: which instruction set architectures provide this ioctl.
+ x86 includes both i386 and x86_64.
+ Parameters: what parameters are accepted by the capability.
+ Returns: the return value. General error numbers (EBADF, ENOMEM, EINVAL)
+ are not detailed, but errors with specific meanings are.
+Architectures: ppc
+Parameters: args[0] is the sPAPR hcall number
+ args[1] is 0 to disable, 1 to enable in-kernel handling
+This capability controls whether individual sPAPR hypercalls (hcalls)
+get handled by the kernel or not. Enabling or disabling in-kernel
+handling of an hcall is effective across the VM. On creation, an
+initial set of hcalls are enabled for in-kernel handling, which
+consists of those hcalls for which in-kernel handlers were implemented
+before this capability was implemented. If disabled, the kernel will
+not to attempt to handle the hcall, but will always exit to userspace
+to handle it. Note that it may not make sense to enable some and
+disable others of a group of related hcalls, but KVM does not prevent
+userspace from doing that.

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