linux-kernel - Re: [PATCH v2 07/10] KVM: arm/arm64: vgic-its: new helper functions to free the caches

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Message-ID: <20171013133516.GJ8927@cbox>
Date:   Fri, 13 Oct 2017 15:35:16 +0200
From:   Christoffer Dall <cdall@...aro.org>
To:     Eric Auger <eric.auger@...hat.com>
Cc:     eric.auger.pro@...il.com, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, marc.zyngier@....com,
        peter.maydell@...aro.org, andre.przywara@....com,
        wanghaibin.wang@...wei.com, wu.wubin@...wei.com
Subject: Re: [PATCH v2 07/10] KVM: arm/arm64: vgic-its: new helper functions
 to free the caches

On Wed, Sep 27, 2017 at 03:28:37PM +0200, Eric Auger wrote:
> From: wanghaibin <wanghaibin.wang@...wei.com>
> 
> We create 2 new functions that frees the device and

           two                   free

> collection lists. this is currently called by vgic_its_destroy()

                    These are

> and we will add other callers in subsequent patches.
> 
> We also remove the check on its->device_list.next as it looks
> unnecessary:

Could you elude to why you're doing this in the first place in the next
version of the commit message?  Thanks.

> 
> The kvm device is removed by kvm_destroy_devices which loops on
> all the devices added to kvm->devices. kvm_ioctl_create_device
> only adds the device to kvm_devices once the lists have been
> initialized (in vgic_create_its).

I don't understand what this paragraph is trying to tell me beyond what
some code already does irrelevant to this patch?

> 
> We also move vgic_its_free_device to prepare for new callers.
> 
> Signed-off-by: wanghaibin <wanghaibin.wang@...wei.com>
> Signed-off-by: Eric Auger <eric.auger@...hat.com>
> 
> ---
> [Eric] removed its->device_list.next which is not needed as
> pointed out by Wanghaibin. Reword the commit message
> ---
>  virt/kvm/arm/vgic/vgic-its.c | 76 ++++++++++++++++++++++++--------------------
>  1 file changed, 41 insertions(+), 35 deletions(-)
> 
> diff --git a/virt/kvm/arm/vgic/vgic-its.c b/virt/kvm/arm/vgic/vgic-its.c
> index 9e6b556..0df6d5f 100644
> --- a/virt/kvm/arm/vgic/vgic-its.c
> +++ b/virt/kvm/arm/vgic/vgic-its.c
> @@ -611,6 +611,45 @@ static void its_free_ite(struct kvm *kvm, struct its_ite *ite)
>  	kfree(ite);
>  }
>  
> +static void vgic_its_free_device(struct kvm *kvm, struct its_device *dev)
> +{
> +	struct its_ite *ite, *tmp;
> +
> +	list_for_each_entry_safe(ite, tmp, &dev->itt_head, ite_list)
> +		its_free_ite(kvm, ite);
> +	list_del(&dev->dev_list);
> +	kfree(dev);
> +}
> +
> +static void vgic_its_free_device_list(struct kvm *kvm, struct vgic_its *its)
> +{
> +	struct list_head *cur, *temp;
> +
> +	mutex_lock(&its->its_lock);
> +	list_for_each_safe(cur, temp, &its->device_list) {
> +		struct its_device *dev;
> +
> +		dev = list_entry(cur, struct its_device, dev_list);
> +		vgic_its_free_device(kvm, dev);
> +	}
> +	mutex_unlock(&its->its_lock);

this changes semantics from locking across freeing both devices and
collections to taking the locks separately.  Is that valid?

> +}
> +
> +static void vgic_its_free_collection_list(struct kvm *kvm, struct vgic_its *its)
> +{
> +	struct list_head *cur, *temp;
> +
> +	list_for_each_safe(cur, temp, &its->collection_list) {
> +		struct its_collection *coll;
> +
> +		coll = list_entry(cur, struct its_collection, coll_list);
> +		list_del(cur);
> +		kfree(coll);
> +	}
> +	mutex_unlock(&its->its_lock);

no mutex_lock ?

> +}
> +
> +
>  static u64 its_cmd_mask_field(u64 *its_cmd, int word, int shift, int size)
>  {
>  	return (le64_to_cpu(its_cmd[word]) >> shift) & (BIT_ULL(size) - 1);
> @@ -1634,46 +1673,13 @@ static int vgic_its_create(struct kvm_device *dev, u32 type)
>  	return vgic_its_set_abi(its, NR_ITS_ABIS - 1);
>  }
>  
> -static void vgic_its_free_device(struct kvm *kvm, struct its_device *dev)
> -{
> -	struct its_ite *ite, *tmp;
> -
> -	list_for_each_entry_safe(ite, tmp, &dev->itt_head, ite_list)
> -		its_free_ite(kvm, ite);
> -	list_del(&dev->dev_list);
> -	kfree(dev);
> -}
> -
>  static void vgic_its_destroy(struct kvm_device *kvm_dev)
>  {
>  	struct kvm *kvm = kvm_dev->kvm;
>  	struct vgic_its *its = kvm_dev->private;
> -	struct list_head *cur, *temp;
> -
> -	/*
> -	 * We may end up here without the lists ever having been initialized.
> -	 * Check this and bail out early to avoid dereferencing a NULL pointer.
> -	 */
> -	if (!its->device_list.next)
> -		return;

I don't think this is valid.  We can actually have a non-initialized
list and without this check, list_for_each_entry_safe in
vgic_its_free_device_list will crash the kernel.

Note that an initialized empty list_head doesn't have head and tail
pointing to NULL, but pointing to the list_head itself.

> -
> -	mutex_lock(&its->its_lock);
> -	list_for_each_safe(cur, temp, &its->device_list) {
> -		struct its_device *dev;
> -
> -		dev = list_entry(cur, struct its_device, dev_list);
> -		vgic_its_free_device(kvm, dev);
> -	}
> -
> -	list_for_each_safe(cur, temp, &its->collection_list) {
> -		struct its_collection *coll;
> -
> -		coll = list_entry(cur, struct its_collection, coll_list);
> -		list_del(cur);
> -		kfree(coll);
> -	}
> -	mutex_unlock(&its->its_lock);
>  
> +	vgic_its_free_device_list(kvm, its);
> +	vgic_its_free_collection_list(kvm, its);
>  	kfree(its);
>  }
>  
> -- 
> 2.5.5
> 

Thanks,
-Christoffer