[PATCH v3 6/8] KVM: s390: Take srcu when importing watchpoint data

[Christian Borntraeger <borntraeger@linux.ibm.com>]

__import_wp_info() backs up the original guest memory contents of a
watchpoint with read_guest_abs(), which is kvm_read_guest() and therefore
resolves the memslot via __kvm_memslots(). That requires kvm->srcu (or
kvm->slots_lock) to be held, otherwise a concurrent memslot update can
free the memslots array under us once its SRCU grace period has elapsed.

As this is not fast path, following lock ordering (mutex first, then
srcu) take the big hammer and hold the srcu for the full import.

Fixes: 27291e2165b6 ("KVM: s390: hardware support for guest debugging")
Cc: stable@vger.kernel.org
Signed-off-by: Christian Borntraeger <borntraeger@linux.ibm.com>
---
 arch/s390/kvm/kvm-s390.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index c47c3a930db7..e0548926dc49 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -4247,8 +4247,10 @@ int kvm_arch_vcpu_ioctl_set_guest_debug(struct kvm_vcpu *vcpu,
 		/* enforce guest PER */
 		kvm_s390_set_cpuflags(vcpu, CPUSTAT_P);
 
-		if (dbg->control & KVM_GUESTDBG_USE_HW_BP)
-			rc = kvm_s390_import_bp_data(vcpu, dbg);
+		if (dbg->control & KVM_GUESTDBG_USE_HW_BP) {
+			scoped_guard(srcu, &vcpu->kvm->srcu)
+				rc = kvm_s390_import_bp_data(vcpu, dbg);
+		}
 	} else {
 		kvm_s390_clear_cpuflags(vcpu, CPUSTAT_P);
 		vcpu->arch.guestdbg.last_bp = 0;
-- 
2.53.0