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SubjectRe: [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

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