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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org,
        Martin Schwidefsky <schwidefsky@de.ibm.com>,
        Christian Borntraeger <borntraeger@de.ibm.com>,
        Janosch Frank <frankja@linux.vnet.ibm.com>,
        David Hildenbrand <david@redhat.com>
Subject: [PATCH 4.9 37/74] KVM: s390: force bp isolation for VSIE
Date:   Fri, 27 Apr 2018 15:58:27 +0200
Message-Id: <20180427135711.467958579@linuxfoundation.org>
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4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Martin Schwidefsky <schwidefsky@de.ibm.com>


From: Christian Borntraeger <borntraeger@de.ibm.com>

[ Upstream commit f315104ad8b0c32be13eac628569ae707c332cb5 ]

If the guest runs with bp isolation when doing a SIE instruction,
we must also run the nested guest with bp isolation when emulating
that SIE instruction.
This is done by activating BPBC in the lpar, which acts as an override
for lower level guests.

Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Reviewed-by: Janosch Frank <frankja@linux.vnet.ibm.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 arch/s390/kvm/vsie.c |   20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

--- a/arch/s390/kvm/vsie.c
+++ b/arch/s390/kvm/vsie.c
@@ -764,6 +764,7 @@ static int do_vsie_run(struct kvm_vcpu *
 {
 	struct kvm_s390_sie_block *scb_s = &vsie_page->scb_s;
 	struct kvm_s390_sie_block *scb_o = vsie_page->scb_o;
+	int guest_bp_isolation;
 	int rc;
 
 	handle_last_fault(vcpu, vsie_page);
@@ -774,6 +775,20 @@ static int do_vsie_run(struct kvm_vcpu *
 		s390_handle_mcck();
 
 	srcu_read_unlock(&vcpu->kvm->srcu, vcpu->srcu_idx);
+
+	/* save current guest state of bp isolation override */
+	guest_bp_isolation = test_thread_flag(TIF_ISOLATE_BP_GUEST);
+
+	/*
+	 * The guest is running with BPBC, so we have to force it on for our
+	 * nested guest. This is done by enabling BPBC globally, so the BPBC
+	 * control in the SCB (which the nested guest can modify) is simply
+	 * ignored.
+	 */
+	if (test_kvm_facility(vcpu->kvm, 82) &&
+	    vcpu->arch.sie_block->fpf & FPF_BPBC)
+		set_thread_flag(TIF_ISOLATE_BP_GUEST);
+
 	local_irq_disable();
 	guest_enter_irqoff();
 	local_irq_enable();
@@ -783,6 +798,11 @@ static int do_vsie_run(struct kvm_vcpu *
 	local_irq_disable();
 	guest_exit_irqoff();
 	local_irq_enable();
+
+	/* restore guest state for bp isolation override */
+	if (!guest_bp_isolation)
+		clear_thread_flag(TIF_ISOLATE_BP_GUEST);
+
 	vcpu->srcu_idx = srcu_read_lock(&vcpu->kvm->srcu);
 
 	if (rc > 0)