[PATCH v4 02/10] powerpc64/ftrace: Disable ftrace during kvm guest entry/exit

["Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>]

During guest entry/exit, we switch over to/from the guest MMU context.
While doing so, we set our state to KVM_GUEST_MODE_HOST_HV to note down
the fact that we cannot take any 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. Once we exit the
guest and restore host MMU context, we re-enable ftrace.

Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
---
 arch/powerpc/kvm/book3s_hv_rmhandlers.S | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/arch/powerpc/kvm/book3s_hv_rmhandlers.S b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
index bd63fa8a08b5..6f2d7206a12b 100644
--- a/arch/powerpc/kvm/book3s_hv_rmhandlers.S
+++ b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
@@ -598,6 +598,10 @@ kvmppc_hv_entry:
 	/* Save R1 in the PACA */
 	std	r1, HSTATE_HOST_R1(r13)
 
+	/* Disable ftrace since we can't take a trap any more */
+	li	r6, 0
+	stb	r6, PACA_FTRACE_ENABLED(r13)
+
 	li	r6, KVM_GUEST_MODE_HOST_HV
 	stb	r6, HSTATE_IN_GUEST(r13)
 
@@ -2078,6 +2082,8 @@ END_FTR_SECTION_IFSET(CPU_FTR_ARCH_300)
 	/* Unset guest mode */
 	li	r0, KVM_GUEST_MODE_NONE
 	stb	r0, HSTATE_IN_GUEST(r13)
+	li	r0, 1
+	stb	r0, PACA_FTRACE_ENABLED(r13)
 
 	lwz	r12, STACK_SLOT_TRAP(r1)	/* return trap # in r12 */
 	ld	r0, SFS+PPC_LR_STKOFF(r1)
@@ -3547,6 +3553,8 @@ END_MMU_FTR_SECTION_IFSET(MMU_FTR_TYPE_RADIX)
 	ld	r8, KVM_HOST_LPCR(r10)
 	mtspr	SPRN_LPCR, r8
 	isync
+	li	r0, 1
+	stb	r0, PACA_FTRACE_ENABLED(r13)
 	li	r0, KVM_GUEST_MODE_NONE
 	stb	r0, HSTATE_IN_GUEST(r13)
 
-- 
2.16.2