powerpc64/ftrace: Disable ftrace during kvm entry/exit

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>

diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index 4d07fca5121c56270aafd6f820009561d399d628..f604cbd8fc3466ccbe2b5ef4d38d91d84d2485be 100644 (file)
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -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();

diff --git a/arch/powerpc/kvm/book3s_hv_rmhandlers.S b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
index bd63fa8a08b5dd3edd0800ac34e483a8501f401c..2c3cbe0067b246bc94aeddf3b34a16ad6fc9484b 100644 (file)
--- a/arch/powerpc/kvm/book3s_hv_rmhandlers.S
+++ b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
@@ -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)