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authorAlexey Kardashevskiy <aik@ozlabs.ru>2016-02-15 12:55:09 +1100
committerPaul Mackerras <paulus@samba.org>2016-02-16 13:44:26 +1100
commitd3695aa4f452bc09c834a5010484f65fca37d87c (patch)
tree57fd47030041118378ea56619fc148f023123fcb /Documentation/virtual
parent5ee7af18642ce38c79b35927872f13d292cc3e27 (diff)
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KVM: PPC: Add support for multiple-TCE hcalls
This adds real and virtual mode handlers for the H_PUT_TCE_INDIRECT and H_STUFF_TCE hypercalls for user space emulated devices such as IBMVIO devices or emulated PCI. These calls allow adding multiple entries (up to 512) into the TCE table in one call which saves time on transition between kernel and user space. The current implementation of kvmppc_h_stuff_tce() allows it to be executed in both real and virtual modes so there is one helper. The kvmppc_rm_h_put_tce_indirect() needs to translate the guest address to the host address and since the translation is different, there are 2 helpers - one for each mode. This implements the KVM_CAP_PPC_MULTITCE capability. When present, the kernel will try handling H_PUT_TCE_INDIRECT and H_STUFF_TCE if these are enabled by the userspace via KVM_CAP_PPC_ENABLE_HCALL. If they can not be handled by the kernel, they are passed on to the user space. The user space still has to have an implementation for these. Both HV and PR-syle KVM are supported. Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru> Reviewed-by: David Gibson <david@gibson.dropbear.id.au> Signed-off-by: Paul Mackerras <paulus@samba.org>
Diffstat (limited to 'Documentation/virtual')
-rw-r--r--Documentation/virtual/kvm/api.txt25
1 files changed, 25 insertions, 0 deletions
diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
index 07e4cdf02407..da3943586a2b 100644
--- a/Documentation/virtual/kvm/api.txt
+++ b/Documentation/virtual/kvm/api.txt
@@ -3035,6 +3035,31 @@ Returns: 0 on success, -1 on error
Queues an SMI on the thread's vcpu.
+4.97 KVM_CAP_PPC_MULTITCE
+
+Capability: KVM_CAP_PPC_MULTITCE
+Architectures: ppc
+Type: vm
+
+This capability means the kernel is capable of handling hypercalls
+H_PUT_TCE_INDIRECT and H_STUFF_TCE without passing those into the user
+space. This significantly accelerates DMA operations for PPC KVM guests.
+User space should expect that its handlers for these hypercalls
+are not going to be called if user space previously registered LIOBN
+in KVM (via KVM_CREATE_SPAPR_TCE or similar calls).
+
+In order to enable H_PUT_TCE_INDIRECT and H_STUFF_TCE use in the guest,
+user space might have to advertise it for the guest. For example,
+IBM pSeries (sPAPR) guest starts using them if "hcall-multi-tce" is
+present in the "ibm,hypertas-functions" device-tree property.
+
+The hypercalls mentioned above may or may not be processed successfully
+in the kernel based fast path. If they can not be handled by the kernel,
+they will get passed on to user space. So user space still has to have
+an implementation for these despite the in kernel acceleration.
+
+This capability is always enabled.
+
5. The kvm_run structure
------------------------