[PATCH v2 2/3] KVM: PPC: Book3S HV: Don't push XIVE context when not using XIVE device

[Paul Mackerras]

At present, when running a guest on POWER9 using HV KVM but not using
an in-kernel interrupt controller (XICS or XIVE), for example if QEMU
is run with the kernel_irqchip=off option, the guest entry code goes
ahead and tries to load the guest context into the XIVE hardware, even
though no context has been set up.

To fix this, we check that the "CAM word" is non-zero before pushing
it to the hardware.  The CAM word is initialized to a non-zero value
in kvmppc_xive_connect_vcpu() and kvmppc_xive_native_connect_vcpu(),
and is now cleared in kvmppc_xive_{,native_}cleanup_vcpu.

Cc: stable at vger.kernel.org # v4.11+
Reported-by: Cédric Le Goater <clg at kaod.org>
Fixes: 5af50993850a ("KVM: PPC: Book3S HV: Native usage of the XIVE interrupt controller")
Signed-off-by: Paul Mackerras <paulus at ozlabs.org>
---
 arch/powerpc/kvm/book3s_hv_rmhandlers.S |  2 ++
 arch/powerpc/kvm/book3s_xive.c          | 11 ++++++++++-
 arch/powerpc/kvm/book3s_xive_native.c   |  3 +++
 3 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/kvm/book3s_hv_rmhandlers.S b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
index 2e7e788..07181d0 100644
--- a/arch/powerpc/kvm/book3s_hv_rmhandlers.S
+++ b/arch/powerpc/kvm/book3s_hv_rmhandlers.S
@@ -942,6 +942,8 @@ ALT_FTR_SECTION_END_IFCLR(CPU_FTR_ARCH_300)
 	ld	r11, VCPU_XIVE_SAVED_STATE(r4)
 	li	r9, TM_QW1_OS
 	lwz	r8, VCPU_XIVE_CAM_WORD(r4)
+	cmpwi	r8, 0
+	beq	no_xive
 	li	r7, TM_QW1_OS + TM_WORD2
 	mfmsr	r0
 	andi.	r0, r0, MSR_DR		/* in real mode? */
diff --git a/arch/powerpc/kvm/book3s_xive.c b/arch/powerpc/kvm/book3s_xive.c
index 09f838a..586867e 100644
--- a/arch/powerpc/kvm/book3s_xive.c
+++ b/arch/powerpc/kvm/book3s_xive.c
@@ -67,8 +67,14 @@ void kvmppc_xive_push_vcpu(struct kvm_vcpu *vcpu)
 	void __iomem *tima = local_paca->kvm_hstate.xive_tima_virt;
 	u64 pq;
 
-	if (!tima)
+	/*
+	 * Nothing to do if the platform doesn't have a XIVE
+	 * or this vCPU doesn't have its own XIVE context
+	 * (e.g. because it's not using an in-kernel interrupt controller).
+	 */
+	if (!tima || !vcpu->arch.xive_cam_word)
 		return;
+
 	eieio();
 	__raw_writeq(vcpu->arch.xive_saved_state.w01, tima + TM_QW1_OS);
 	__raw_writel(vcpu->arch.xive_cam_word, tima + TM_QW1_OS + TM_WORD2);
@@ -1146,6 +1152,9 @@ void kvmppc_xive_cleanup_vcpu(struct kvm_vcpu *vcpu)
 	/* Disable the VP */
 	xive_native_disable_vp(xc->vp_id);
 
+	/* Clear the cam word so guest entry won't try to push context */
+	vcpu->arch.xive_cam_word = 0;
+
 	/* Free the queues */
 	for (i = 0; i < KVMPPC_XIVE_Q_COUNT; i++) {
 		struct xive_q *q = &xc->queues[i];
diff --git a/arch/powerpc/kvm/book3s_xive_native.c b/arch/powerpc/kvm/book3s_xive_native.c
index 368427f..11b91b4 100644
--- a/arch/powerpc/kvm/book3s_xive_native.c
+++ b/arch/powerpc/kvm/book3s_xive_native.c
@@ -81,6 +81,9 @@ void kvmppc_xive_native_cleanup_vcpu(struct kvm_vcpu *vcpu)
 	/* Disable the VP */
 	xive_native_disable_vp(xc->vp_id);
 
+	/* Clear the cam word so guest entry won't try to push context */
+	vcpu->arch.xive_cam_word = 0;
+
 	/* Free the queues */
 	for (i = 0; i < KVMPPC_XIVE_Q_COUNT; i++) {
 		kvmppc_xive_native_cleanup_queue(vcpu, i);
-- 
2.7.4