From: Marc Zyngier <marc.zyngier@arm.com>
Date: Tue, 19 Mar 2019 12:47:11 +0000
Subject: KVM: arm/arm64: vgic-its: Take the srcu lock when writing to guest
 memory
Patch-mainline: v5.1-rc3
Git-commit: a6ecfb11bf37743c1ac49b266595582b107b61d4
References: bsc#1133021

When halting a guest, QEMU flushes the virtual ITS caches, which
amounts to writing to the various tables that the guest has allocated.

When doing this, we fail to take the srcu lock, and the kernel
shouts loudly if running a lockdep kernel:

[   69.680416] =============================
[   69.680819] WARNING: suspicious RCU usage
[   69.681526] 5.1.0-rc1-00008-g600025238f51-dirty #18 Not tainted
[   69.682096] -----------------------------
[   69.682501] ./include/linux/kvm_host.h:605 suspicious rcu_dereference_check() usage!
[   69.683225]
[   69.683225] other info that might help us debug this:
[   69.683225]
[   69.683975]
[   69.683975] rcu_scheduler_active = 2, debug_locks = 1
[   69.684598] 6 locks held by qemu-system-aar/4097:
[   69.685059]  #0: 0000000034196013 (&kvm->lock){+.+.}, at: vgic_its_set_attr+0x244/0x3a0
[   69.686087]  #1: 00000000f2ed935e (&its->its_lock){+.+.}, at: vgic_its_set_attr+0x250/0x3a0
[   69.686919]  #2: 000000005e71ea54 (&vcpu->mutex){+.+.}, at: lock_all_vcpus+0x64/0xd0
[   69.687698]  #3: 00000000c17e548d (&vcpu->mutex){+.+.}, at: lock_all_vcpus+0x64/0xd0
[   69.688475]  #4: 00000000ba386017 (&vcpu->mutex){+.+.}, at: lock_all_vcpus+0x64/0xd0
[   69.689978]  #5: 00000000c2c3c335 (&vcpu->mutex){+.+.}, at: lock_all_vcpus+0x64/0xd0
[   69.690729]
[   69.690729] stack backtrace:
[   69.691151] CPU: 2 PID: 4097 Comm: qemu-system-aar Not tainted 5.1.0-rc1-00008-g600025238f51-dirty #18
[   69.691984] Hardware name: rockchip evb_rk3399/evb_rk3399, BIOS 2019.04-rc3-00124-g2feec69fb1 03/15/2019
[   69.692831] Call trace:
[   69.694072]  lockdep_rcu_suspicious+0xcc/0x110
[   69.694490]  gfn_to_memslot+0x174/0x190
[   69.694853]  kvm_write_guest+0x50/0xb0
[   69.695209]  vgic_its_save_tables_v0+0x248/0x330
[   69.695639]  vgic_its_set_attr+0x298/0x3a0
[   69.696024]  kvm_device_ioctl_attr+0x9c/0xd8
[   69.696424]  kvm_device_ioctl+0x8c/0xf8
[   69.696788]  do_vfs_ioctl+0xc8/0x960
[   69.697128]  ksys_ioctl+0x8c/0xa0
[   69.697445]  __arm64_sys_ioctl+0x28/0x38
[   69.697817]  el0_svc_common+0xd8/0x138
[   69.698173]  el0_svc_handler+0x38/0x78
[   69.698528]  el0_svc+0x8/0xc

The fix is to obviously take the srcu lock, just like we do on the
read side of things since bf308242ab98. One wonders why this wasn't
fixed at the same time, but hey...

Fixes: bf308242ab98 ("KVM: arm/arm64: VGIC/ITS: protect kvm_read_guest() calls with SRCU lock")
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Acked-by: Liang Yan <lyan@suse.com>
---
 arch/arm/include/asm/kvm_mmu.h   |   11 +++++++++++
 arch/arm64/include/asm/kvm_mmu.h |   11 +++++++++++
 virt/kvm/arm/vgic/vgic-its.c     |    8 ++++----
 virt/kvm/arm/vgic/vgic-v3.c      |    4 ++--
 4 files changed, 28 insertions(+), 6 deletions(-)

--- a/arch/arm/include/asm/kvm_mmu.h
+++ b/arch/arm/include/asm/kvm_mmu.h
@@ -244,6 +244,17 @@ static inline int kvm_read_guest_lock(st
 	return ret;
 }
 
+static inline int kvm_write_guest_lock(struct kvm *kvm, gpa_t gpa,
+				       const void *data, unsigned long len)
+{
+	int srcu_idx = srcu_read_lock(&kvm->srcu);
+	int ret = kvm_write_guest(kvm, gpa, data, len);
+
+	srcu_read_unlock(&kvm->srcu, srcu_idx);
+
+	return ret;
+}
+
 static inline void *kvm_get_hyp_vector(void)
 {
 	switch(read_cpuid_part()) {
--- a/arch/arm64/include/asm/kvm_mmu.h
+++ b/arch/arm64/include/asm/kvm_mmu.h
@@ -340,6 +340,17 @@ static inline int kvm_read_guest_lock(st
 	return ret;
 }
 
+static inline int kvm_write_guest_lock(struct kvm *kvm, gpa_t gpa,
+                                       const void *data, unsigned long len)
+{
+       int srcu_idx = srcu_read_lock(&kvm->srcu);
+       int ret = kvm_write_guest(kvm, gpa, data, len);
+
+       srcu_read_unlock(&kvm->srcu, srcu_idx);
+
+       return ret;
+}
+
 #ifdef CONFIG_HARDEN_BRANCH_PREDICTOR
 #include <asm/mmu.h>
 
--- a/virt/kvm/arm/vgic/vgic-its.c
+++ b/virt/kvm/arm/vgic/vgic-its.c
@@ -1930,7 +1930,7 @@ static int vgic_its_save_ite(struct vgic
 	       ((u64)ite->irq->intid << KVM_ITS_ITE_PINTID_SHIFT) |
 		ite->collection->collection_id;
 	val = cpu_to_le64(val);
-	return kvm_write_guest(kvm, gpa, &val, ite_esz);
+	return kvm_write_guest_lock(kvm, gpa, &val, ite_esz);
 }
 
 /**
@@ -2077,7 +2077,7 @@ static int vgic_its_save_dte(struct vgic
 	       (itt_addr_field << KVM_ITS_DTE_ITTADDR_SHIFT) |
 		(dev->num_eventid_bits - 1));
 	val = cpu_to_le64(val);
-	return kvm_write_guest(kvm, ptr, &val, dte_esz);
+	return kvm_write_guest_lock(kvm, ptr, &val, dte_esz);
 }
 
 /**
@@ -2257,7 +2257,7 @@ static int vgic_its_save_cte(struct vgic
 	       ((u64)collection->target_addr << KVM_ITS_CTE_RDBASE_SHIFT) |
 	       collection->collection_id);
 	val = cpu_to_le64(val);
-	return kvm_write_guest(its->dev->kvm, gpa, &val, esz);
+	return kvm_write_guest_lock(its->dev->kvm, gpa, &val, esz);
 }
 
 static int vgic_its_restore_cte(struct vgic_its *its, gpa_t gpa, int esz)
@@ -2328,7 +2328,7 @@ static int vgic_its_save_collection_tabl
 	 */
 	val = 0;
 	BUG_ON(cte_esz > sizeof(val));
-	ret = kvm_write_guest(its->dev->kvm, gpa, &val, cte_esz);
+	ret = kvm_write_guest_lock(its->dev->kvm, gpa, &val, cte_esz);
 	return ret;
 }
 
--- a/virt/kvm/arm/vgic/vgic-v3.c
+++ b/virt/kvm/arm/vgic/vgic-v3.c
@@ -317,7 +317,7 @@ retry:
 	if (status) {
 		/* clear consumed data */
 		val &= ~(1 << bit_nr);
-		ret = kvm_write_guest(kvm, ptr, &val, 1);
+		ret = kvm_write_guest_lock(kvm, ptr, &val, 1);
 		if (ret)
 			return ret;
 	}
@@ -368,7 +368,7 @@ int vgic_v3_save_pending_tables(struct k
 		else
 			val &= ~(1 << bit_nr);
 
-		ret = kvm_write_guest(kvm, ptr, &val, 1);
+		ret = kvm_write_guest_lock(kvm, ptr, &val, 1);
 		if (ret)
 			return ret;
 	}