On Thu, Jan 11, 2018 at 06:11:38PM +0800, wei.guo.simon@xxxxxxxxx wrote: > From: Simon Guo <wei.guo.simon@xxxxxxxxx> > > Currently guest kernel doesn't handle TAR fac unavailable and it always > runs with TAR bit on. PR KVM will lazily enable TAR. TAR is not a > frequent-use reg and it is not included in SVCPU struct. > > To make it work for transaction memory at PR KVM: > 1). Flush/giveup TAR at kvmppc_save_tm_pr(). > 2) If we are receiving a TAR fac unavail exception inside a transaction, > the checkpointed TAR might be a TAR value from another process. So we need > treclaim the transaction, then load the desired TAR value into reg, and > perform trecheckpoint. > 3) Load TAR facility at kvmppc_restore_tm_pr() when TM active. > The reason we always loads TAR when restoring TM is that: > If we don't do this way, when there is a TAR fac unavailable exception > during TM active: > case 1: it is the 1st TAR fac unavail exception after tbegin. > vcpu->arch.tar should be reloaded as checkpoint tar val. > case 2: it is the 2nd or later TAR fac unavail exception after tbegin. > vcpu->arch.tar_tm should be reloaded as checkpoint tar val. > There will be unnecessary difficulty to handle the above 2 cases. > > at the end of emulating treclaim., the correct TAR val need to be loaded > into reg if FSCR_TAR bit is on. > at the beginning of emulating trechkpt., TAR needs to be flushed so that > the right tar val can be copy into tar_tm. Would it be simpler always to load up TAR when guest_MSR[TM] is 1? Paul.
