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Patch "KVM: s390: add proper locking for CMMA migration bitmap" has been added to the 4.14-stable tree

PATCH [email protected] 1 participant 1 message Jan 26, 2018

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This is a note to let you know that I've just added the patch titled

KVM: s390: add proper locking for CMMA migration bitmap

to the 4.14-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
kvm-s390-add-proper-locking-for-cmma-migration-bitmap.patch
and it can be found in the queue-4.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

Quoted 1 line

From 1de1ea7efeb9e8543212210e34518b4049ccd285 Mon Sep 17 00:00:00 2001

From: Christian Borntraeger <[email protected]>
Date: Fri, 22 Dec 2017 10:54:20 +0100
Subject: KVM: s390: add proper locking for CMMA migration bitmap

From: Christian Borntraeger <[email protected]>

commit 1de1ea7efeb9e8543212210e34518b4049ccd285 upstream.

Some parts of the cmma migration bitmap is already protected with the kvm->lock (e.g. the migration start). On the other hand the read of the cmma bits is not protected against a concurrent free, neither is the emulation of the ESSA instruction. Let's extend the locking to all related ioctls by using the slots lock for
- kvm_s390_vm_start_migration
- kvm_s390_vm_stop_migration
- kvm_s390_set_cmma_bits
- kvm_s390_get_cmma_bits

In addition to that, we use synchronize_srcu before freeing the migration structure as all users hold kvm->srcu for read. (e.g. the ESSA handler).

Reported-by David Hildenbrand <[email protected]>
Signed-off-by Christian Borntraeger <[email protected]>
Fixes 190df4a212a7 (KVM: s390: CMMA tracking, ESSA emulation, migration mode)
Reviewed-by Claudio Imbrenda <[email protected]>
Reviewed-by David Hildenbrand <[email protected]>
Reviewed-by Cornelia Huck <[email protected]>
Signed-off-by Greg Kroah-Hartman <[email protected]>
---
 arch/s390/kvm/kvm-s390.c |   18 +++++++++++-------
 1 file changed, 11 insertions(+), 7 deletions(-)
arch/s390/kvm/kvm-s390.c +11 -7
@@ -768,7 +768,7 @@ static void kvm_s390_sync_request_broadc
 
 /*
  * Must be called with kvm->srcu held to avoid races on memslots, and with
- * kvm->lock to avoid races with ourselves and kvm_s390_vm_stop_migration.
+ * kvm->slots_lock to avoid races with ourselves and kvm_s390_vm_stop_migration.
  */
 static int kvm_s390_vm_start_migration(struct kvm *kvm)
 {

@@ -824,7 +824,7 @@ static int kvm_s390_vm_start_migration(s
 }
 
 /*
- * Must be called with kvm->lock to avoid races with ourselves and
+ * Must be called with kvm->slots_lock to avoid races with ourselves and
  * kvm_s390_vm_start_migration.
  */
 static int kvm_s390_vm_stop_migration(struct kvm *kvm)

@@ -839,6 +839,8 @@ static int kvm_s390_vm_stop_migration(st
 
 	if (kvm->arch.use_cmma) {
 		kvm_s390_sync_request_broadcast(kvm, KVM_REQ_STOP_MIGRATION);
+		/* We have to wait for the essa emulation to finish */
+		synchronize_srcu(&kvm->srcu);
 		vfree(mgs->pgste_bitmap);
 	}
 	kfree(mgs);

@@ -848,14 +850,12 @@ static int kvm_s390_vm_stop_migration(st
 static int kvm_s390_vm_set_migration(struct kvm *kvm,
 				     struct kvm_device_attr *attr)
 {
-	int idx, res = -ENXIO;
+	int res = -ENXIO;
 
-	mutex_lock(&kvm->lock);
+	mutex_lock(&kvm->slots_lock);
 	switch (attr->attr) {
 	case KVM_S390_VM_MIGRATION_START:
-		idx = srcu_read_lock(&kvm->srcu);
 		res = kvm_s390_vm_start_migration(kvm);
-		srcu_read_unlock(&kvm->srcu, idx);
 		break;
 	case KVM_S390_VM_MIGRATION_STOP:
 		res = kvm_s390_vm_stop_migration(kvm);

@@ -863,7 +863,7 @@ static int kvm_s390_vm_set_migration(str
 	default:
 		break;
 	}
-	mutex_unlock(&kvm->lock);
+	mutex_unlock(&kvm->slots_lock);
 
 	return res;
 }

@@ -1753,7 +1753,9 @@ long kvm_arch_vm_ioctl(struct file *filp
 		r = -EFAULT;
 		if (copy_from_user(&args, argp, sizeof(args)))
 			break;
+		mutex_lock(&kvm->slots_lock);
 		r = kvm_s390_get_cmma_bits(kvm, &args);
+		mutex_unlock(&kvm->slots_lock);
 		if (!r) {
 			r = copy_to_user(argp, &args, sizeof(args));
 			if (r)

@@ -1767,7 +1769,9 @@ long kvm_arch_vm_ioctl(struct file *filp
 		r = -EFAULT;
 		if (copy_from_user(&args, argp, sizeof(args)))
 			break;
+		mutex_lock(&kvm->slots_lock);
 		r = kvm_s390_set_cmma_bits(kvm, &args);
+		mutex_unlock(&kvm->slots_lock);
 		break;
 	}
 	default:

Patches currently in stable-queue which might be from [email protected] are

queue-4.14/kvm-s390-add-proper-locking-for-cmma-migration-bitmap.patch