[PATCH AUTOSEL 5.7 288/388] KVM: PPC: Book3S: Fix some RCU-list locks

Sasha Levin
2020-06-18T02:35:12Z

From: Qian Cai <cai@lca.pw>

[ Upstream commit ab8b65be183180c3eef405d449163964ecc4b571 ]

It is unsafe to traverse kvm->arch.spapr_tce_tables and
stt->iommu_tables without the RCU read lock held. Also, add
cond_resched_rcu() in places with the RCU read lock held that could take
a while to finish.

arch/powerpc/kvm/book3s_64_vio.c:76 RCU-list traversed in non-reader section!!

other info that might help us debug this:

rcu_scheduler_active = 2, debug_locks = 1
no locks held by qemu-kvm/4265.

stack backtrace:
CPU: 96 PID: 4265 Comm: qemu-kvm Not tainted 5.7.0-rc4-next-20200508+ #2
Call Trace:
[c000201a8690f720] [c000000000715948] dump_stack+0xfc/0x174 (unreliable)
[c000201a8690f770] [c0000000001d9470] lockdep_rcu_suspicious+0x140/0x164
[c000201a8690f7f0] [c008000010b9fb48] kvm_spapr_tce_release_iommu_group+0x1f0/0x220 [kvm]
[c000201a8690f870] [c008000010b8462c] kvm_spapr_tce_release_vfio_group+0x54/0xb0 [kvm]
[c000201a8690f8a0] [c008000010b84710] kvm_vfio_destroy+0x88/0x140 [kvm]
[c000201a8690f8f0] [c008000010b7d488] kvm_put_kvm+0x370/0x600 [kvm]
[c000201a8690f990] [c008000010b7e3c0] kvm_vm_release+0x38/0x60 [kvm]
[c000201a8690f9c0] [c0000000005223f4] __fput+0x124/0x330
[c000201a8690fa20] [c000000000151cd8] task_work_run+0xb8/0x130
[c000201a8690fa70] [c0000000001197e8] do_exit+0x4e8/0xfa0
[c000201a8690fb70] [c00000000011a374] do_group_exit+0x64/0xd0
[c000201a8690fbb0] [c000000000132c90] get_signal+0x1f0/0x1200
[c000201a8690fcc0] [c000000000020690] do_notify_resume+0x130/0x3c0
[c000201a8690fda0] [c000000000038d64] syscall_exit_prepare+0x1a4/0x280
[c000201a8690fe20] [c00000000000c8f8] system_call_common+0xf8/0x278

====
arch/powerpc/kvm/book3s_64_vio.c:368 RCU-list traversed in non-reader section!!

other info that might help us debug this:

rcu_scheduler_active = 2, debug_locks = 1
2 locks held by qemu-kvm/4264:
#0: c000201ae2d000d8 (&vcpu->mutex){+.+.}-{3:3}, at: kvm_vcpu_ioctl+0xdc/0x950 [kvm]
#1: c000200c9ed0c468 (&kvm->srcu){....}-{0:0}, at: kvmppc_h_put_tce+0x88/0x340 [kvm]

====
arch/powerpc/kvm/book3s_64_vio.c:108 RCU-list traversed in non-reader section!!

other info that might help us debug this:

rcu_scheduler_active = 2, debug_locks = 1
1 lock held by qemu-kvm/4257:
#0: c000200b1b363a40 (&kv->lock){+.+.}-{3:3}, at: kvm_vfio_set_attr+0x598/0x6c0 [kvm]

====
arch/powerpc/kvm/book3s_64_vio.c:146 RCU-list traversed in non-reader section!!

other info that might help us debug this:

rcu_scheduler_active = 2, debug_locks = 1
1 lock held by qemu-kvm/4257:
#0: c000200b1b363a40 (&kv->lock){+.+.}-{3:3}, at: kvm_vfio_set_attr+0x598/0x6c0 [kvm]

Signed-off-by: Qian Cai <cai@lca.pw>
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/powerpc/kvm/book3s_64_vio.c | 18 ++++++++++++++----
1 file changed, 14 insertions(+), 4 deletions(-)

diff --git a/arch/powerpc/kvm/book3s_64_vio.c b/arch/powerpc/kvm/book3s_64_vio.c
index 50555ad1db93..1a529df0ab44 100644
--- a/arch/powerpc/kvm/book3s_64_vio.c
+++ b/arch/powerpc/kvm/book3s_64_vio.c
@@ -73,6 +73,7 @@ extern void kvm_spapr_tce_release_iommu_group(struct kvm *kvm,
struct kvmppc_spapr_tce_iommu_table *stit, *tmp;
struct iommu_table_group *table_group = NULL;

+ rcu_read_lock();
list_for_each_entry_rcu(stt, &kvm->arch.spapr_tce_tables, list) {

table_group = iommu_group_get_iommudata(grp);
@@ -87,7 +88,9 @@ extern void kvm_spapr_tce_release_iommu_group(struct kvm *kvm,
kref_put(&stit->kref, kvm_spapr_tce_liobn_put);
}
}
+ cond_resched_rcu();
}
+ rcu_read_unlock();
}

extern long kvm_spapr_tce_attach_iommu_group(struct kvm *kvm, int tablefd,
@@ -105,12 +108,14 @@ extern long kvm_spapr_tce_attach_iommu_group(struct kvm *kvm, int tablefd,
if (!f.file)
return -EBADF;

+ rcu_read_lock();
list_for_each_entry_rcu(stt, &kvm->arch.spapr_tce_tables, list) {
if (stt == f.file->private_data) {
found = true;
break;
}
}
+ rcu_read_unlock();

fdput(f);

@@ -143,6 +148,7 @@ extern long kvm_spapr_tce_attach_iommu_group(struct kvm *kvm, int tablefd,
if (!tbl)
return -EINVAL;

+ rcu_read_lock();
list_for_each_entry_rcu(stit, &stt->iommu_tables, next) {
if (tbl != stit->tbl)
continue;
@@ -150,14 +156,17 @@ extern long kvm_spapr_tce_attach_iommu_group(struct kvm *kvm, int tablefd,
if (!kref_get_unless_zero(&stit->kref)) {
/* stit is being destroyed */
iommu_tce_table_put(tbl);
+ rcu_read_unlock();
return -ENOTTY;
}
/*
* The table is already known to this KVM, we just increased
* its KVM reference counter and can return.
*/
+ rcu_read_unlock();
return 0;
}
+ rcu_read_unlock();

stit = kzalloc(sizeof(*stit), GFP_KERNEL);
if (!stit) {
@@ -365,18 +374,19 @@ static long kvmppc_tce_validate(struct kvmppc_spapr_tce_table *stt,
if (kvmppc_tce_to_ua(stt->kvm, tce, &ua))
return H_TOO_HARD;

+ rcu_read_lock();
list_for_each_entry_rcu(stit, &stt->iommu_tables, next) {
unsigned long hpa = 0;
struct mm_iommu_table_group_mem_t *mem;
long shift = stit->tbl->it_page_shift;

mem = mm_iommu_lookup(stt->kvm->mm, ua, 1ULL << shift);
- if (!mem)
- return H_TOO_HARD;
-
- if (mm_iommu_ua_to_hpa(mem, ua, shift, &hpa))
+ if (!mem || mm_iommu_ua_to_hpa(mem, ua, shift, &hpa)) {
+ rcu_read_unlock();
return H_TOO_HARD;
+ }
}
+ rcu_read_unlock();

return H_SUCCESS;
}
--
2.25.1