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powerpc64/ftrace: Disable ftrace during kvm entry/exit

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During guest entry/exit, we switch over to/from the guest MMU context
and we cannot take exceptions in the hypervisor code.

Since ftrace may be enabled and since it can result in us taking a trap,
disable ftrace by setting paca->ftrace_enabled to zero. There are two
paths through which we enter/exit a guest:
1. If we are the vcore runner, then we enter the guest via
__kvmppc_vcore_entry() and we disable ftrace around this. This is always
the case for Power9, and for the primary thread on Power8.
2. If we are a secondary thread in Power8, then we would be in nap due
to SMT being disabled. We are woken up by an IPI to enter the guest. In
this scenario, we enter the guest through kvm_start_guest(). We disable
ftrace at this point. In this scenario, ftrace would only get re-enabled
on the secondary thread when SMT is re-enabled (via start_secondary()).

Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
This commit is contained in:
Naveen N. Rao 2018-04-19 12:34:05 +05:30 committed by Michael Ellerman
parent 424ef0160f
commit a4bc64d305
2 changed files with 7 additions and 0 deletions
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4
arch/powerpc/kvm/book3s_hv.c
View file

@ -2911,8 +2911,12 @@ static noinline void kvmppc_run_core(struct kvmppc_vcore *vc)
srcu_idx = srcu_read_lock(&vc->kvm->srcu);
this_cpu_disable_ftrace();
trap = __kvmppc_vcore_entry();
this_cpu_enable_ftrace();
srcu_read_unlock(&vc->kvm->srcu, srcu_idx);
trace_hardirqs_off();

3
arch/powerpc/kvm/book3s_hv_rmhandlers.S
View file

@ -342,6 +342,9 @@ kvm_start_guest:
ld r2,PACATOC(r13)
li r0,0
stb r0,PACA_FTRACE_ENABLED(r13)
li r0,KVM_HWTHREAD_IN_KVM
stb r0,HSTATE_HWTHREAD_STATE(r13)