From 93b0f4dc29c5f077a1c97bd1d484147230c3779a Mon Sep 17 00:00:00 2001 From: Paul Mackerras Date: Fri, 6 Sep 2013 13:17:46 +1000 Subject: KVM: PPC: Book3S HV: Implement timebase offset for guests This allows guests to have a different timebase origin from the host. This is needed for migration, where a guest can migrate from one host to another and the two hosts might have a different timebase origin. However, the timebase seen by the guest must not go backwards, and should go forwards only by a small amount corresponding to the time taken for the migration. Therefore this provides a new per-vcpu value accessed via the one_reg interface using the new KVM_REG_PPC_TB_OFFSET identifier. This value defaults to 0 and is not modified by KVM. On entering the guest, this value is added onto the timebase, and on exiting the guest, it is subtracted from the timebase. This is only supported for recent POWER hardware which has the TBU40 (timebase upper 40 bits) register. Writing to the TBU40 register only alters the upper 40 bits of the timebase, leaving the lower 24 bits unchanged. This provides a way to modify the timebase for guest migration without disturbing the synchronization of the timebase registers across CPU cores. The kernel rounds up the value given to a multiple of 2^24. Timebase values stored in KVM structures (struct kvm_vcpu, struct kvmppc_vcore, etc.) are stored as host timebase values. The timebase values in the dispatch trace log need to be guest timebase values, however, since that is read directly by the guest. This moves the setting of vcpu->arch.dec_expires on guest exit to a point after we have restored the host timebase so that vcpu->arch.dec_expires is a host timebase value. Signed-off-by: Paul Mackerras Signed-off-by: Alexander Graf --- Documentation/virtual/kvm/api.txt | 1 + 1 file changed, 1 insertion(+) (limited to 'Documentation/virtual') diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt index 354a51ba456b..e43c6f14c225 100644 --- a/Documentation/virtual/kvm/api.txt +++ b/Documentation/virtual/kvm/api.txt @@ -1810,6 +1810,7 @@ registers, find a list below: PPC | KVM_REG_PPC_TLB3PS | 32 PPC | KVM_REG_PPC_EPTCFG | 32 PPC | KVM_REG_PPC_ICP_STATE | 64 + PPC | KVM_REG_PPC_TB_OFFSET | 64 PPC | KVM_REG_PPC_SPMC1 | 32 PPC | KVM_REG_PPC_SPMC2 | 32 PPC | KVM_REG_PPC_IAMR | 64 -- cgit v1.2.3