linux-kernel - Re: [PATCH v2 3/4] iommu/ioasid: Add custom allocators

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Date:   Wed, 2 Oct 2019 18:18:25 +0200
From:   Jean-Philippe Brucker <jean-philippe@...aro.org>
To:     Jacob Pan <jacob.jun.pan@...ux.intel.com>
Cc:     iommu@...ts.linux-foundation.org,
        LKML <linux-kernel@...r.kernel.org>,
        Joerg Roedel <joro@...tes.org>,
        David Woodhouse <dwmw2@...radead.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        Jean-Philippe Brucker <jean-philippe@...aro.com>,
        Yi Liu <yi.l.liu@...el.com>,
        "Tian, Kevin" <kevin.tian@...el.com>,
        Raj Ashok <ashok.raj@...el.com>,
        Christoph Hellwig <hch@...radead.org>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Jonathan Cameron <jic23@...nel.org>,
        Eric Auger <eric.auger@...hat.com>
Subject: Re: [PATCH v2 3/4] iommu/ioasid: Add custom allocators

Hi Jacob,

I have four tiny comments below but the patch looks great otherwise, no
major concern from me.

On Sat, Sep 21, 2019 at 05:07:49PM -0700, Jacob Pan wrote:
> +/*
> + * struct ioasid_allocator_data - Internal data structure to hold information
> + * about an allocator. There are two types of allocators:
> + *
> + * - Default allocator always has its own XArray to track the IOASIDs allocated.
> + * - Custom allocators may share allocation helpers with different private data.
> + *   Custom allocators that share the same helper functions also share the same
> + *   XArray.
> + * Rules:
> + * 1. Default allocator is always available, not dynamically registered. This is
> + *    to prevent race conditions with early boot code that want to register
> + *    custom allocators or allocate IOASIDs.
> + * 2. Custom allocators take precedence over the default allocator.
> + * 3. When all custom allocators sharing the same helper functions are
> + *    unregistered (e.g. due to hotplug), all outstanding IOASIDs must be
> + *    freed. Otherwise, outstand IOASIDs will be lost and orphaned.

                           outstanding

[...]
>  ioasid_t ioasid_alloc(struct ioasid_set *set, ioasid_t min, ioasid_t max,
>  		      void *private)
>  {
> -	ioasid_t id;
>  	struct ioasid_data *data;
> +	void *adata;
> +	ioasid_t id;

nit: changing the location of id could be in patch 2/4.

> -	data = kzalloc(sizeof(*data), GFP_KERNEL);
> +	data = kzalloc(sizeof(*data), GFP_ATOMIC);

I don't think that one needs to be GFP_ATOMIC. Otherwise it should
probably be done from the start, by patch 2/4.

>  	if (!data)
>  		return INVALID_IOASID;
>  
>  	data->set = set;
>  	data->private = private;
>  
> -	if (xa_alloc(&ioasid_xa, &id, data, XA_LIMIT(min, max), GFP_KERNEL)) {
> -		pr_err("Failed to alloc ioasid from %d to %d\n", min, max);
> +	/*
> +	 * Custom allocator needs allocator data to perform platform specific
> +	 * operations.
> +	 */
> +	spin_lock(&ioasid_allocator_lock);
> +	adata = active_allocator->flags & IOASID_ALLOCATOR_CUSTOM ? active_allocator->ops->pdata : data;
> +	id = active_allocator->ops->alloc(min, max, adata);
> +	if (id == INVALID_IOASID) {
> +		pr_err("Failed ASID allocation %lu\n", active_allocator->flags);
> +		goto exit_free;
> +	}
> +
> +	if ((active_allocator->flags & IOASID_ALLOCATOR_CUSTOM) &&
> +		xa_alloc(&active_allocator->xa, &id, data, XA_LIMIT(id, id), GFP_ATOMIC)) {

nit: aligning at the "if (" would make this block more readable.

> +		/* Custom allocator needs framework to store and track allocation results */
> +		pr_err("Failed to alloc ioasid from %d\n", id);
> +		active_allocator->ops->free(id, active_allocator->ops->pdata);
>  		goto exit_free;
>  	}

Thanks,
Jean