Re: [PATCH v2 01/10] iommu/vt-d: add wrapper functions for page allocations

Liu, Jingqi
2023-12-26T06:10:48Z

On 12/15/2023 3:16 AM, Pasha Tatashin wrote:
> On Thu, Dec 14, 2023 at 12:58 PM David Rientjes <rientjes@google.com> wrote:
>>
>> On Thu, 30 Nov 2023, Pasha Tatashin wrote:
>>
>>> diff --git a/drivers/iommu/iommu-pages.h b/drivers/iommu/iommu-pages.h
>>> new file mode 100644
>>> index 000000000000..2332f807d514
>>> --- /dev/null
>>> +++ b/drivers/iommu/iommu-pages.h
>>> @@ -0,0 +1,199 @@
>>> +/* SPDX-License-Identifier: GPL-2.0-only */
>>> +/*
>>> + * Copyright (c) 2023, Google LLC.
>>> + * Pasha Tatashin <pasha.tatashin@soleen.com>
>>> + */
>>> +
>>> +#ifndef __IOMMU_PAGES_H
>>> +#define __IOMMU_PAGES_H
>>> +
>>> +#include <linux/vmstat.h>
>>> +#include <linux/gfp.h>
>>> +#include <linux/mm.h>
>>> +
>>> +/*
>>> + * All page allocation that are performed in the IOMMU subsystem must use one of
>>> + * the functions below. This is necessary for the proper accounting as IOMMU
>>> + * state can be rather large, i.e. multiple gigabytes in size.
>>> + */
>>> +
>>> +/**
>>> + * __iommu_alloc_pages_node - allocate a zeroed page of a given order from
>>> + * specific NUMA node.
>>> + * @nid: memory NUMA node id
>>
>> NUMA_NO_NODE if no locality requirements?
>
> If no locality is required, there is a better interface:
> __iommu_alloc_pages(). That one will also take a look at the calling
> process policies to determine the proper NUMA node when nothing is
> specified. However, when policies should be ignored, and no locality
> required, NUMA_NO_NODE can be passed.
>
>>
>>> + * @gfp: buddy allocator flags
>>> + * @order: page order
>>> + *
>>> + * returns the head struct page of the allocated page.
>>> + */
>>> +static inline struct page *__iommu_alloc_pages_node(int nid, gfp_t gfp,
>>> + int order)
>>> +{
>>> + struct page *pages;
>>
>> s/pages/page/ here and later in this file.
>
> In this file, where there a page with an "order", I reference it with
> "pages", when no order (i.e. order = 0), I reference it with "page"
>
> I.e.: __iommu_alloc_page vs. __iommu_alloc_pages
>
>>
>>> +
>>> + pages = alloc_pages_node(nid, gfp | __GFP_ZERO, order);
>>> + if (!pages)
>>
>> unlikely()?
>
> Will add it.
>
>>
>>> + return NULL;
>>> +
>>> + return pages;
>>> +}
>>> +
>>> +/**
>>> + * __iommu_alloc_pages - allocate a zeroed page of a given order.
>>> + * @gfp: buddy allocator flags
>>> + * @order: page order
>>> + *
>>> + * returns the head struct page of the allocated page.
>>> + */
>>> +static inline struct page *__iommu_alloc_pages(gfp_t gfp, int order)
>>> +{
>>> + struct page *pages;
>>> +
>>> + pages = alloc_pages(gfp | __GFP_ZERO, order);
>>> + if (!pages)
>>> + return NULL;
>>> +
>>> + return pages;
>>> +}
>>> +
>>> +/**
>>> + * __iommu_alloc_page_node - allocate a zeroed page at specific NUMA node.
>>> + * @nid: memory NUMA node id
>>> + * @gfp: buddy allocator flags
>>> + *
>>> + * returns the struct page of the allocated page.
>>> + */
>>> +static inline struct page *__iommu_alloc_page_node(int nid, gfp_t gfp)
>>> +{
>>> + return __iommu_alloc_pages_node(nid, gfp, 0);
>>> +}
>>> +
>>> +/**
>>> + * __iommu_alloc_page - allocate a zeroed page
>>> + * @gfp: buddy allocator flags
>>> + *
>>> + * returns the struct page of the allocated page.
>>> + */
>>> +static inline struct page *__iommu_alloc_page(gfp_t gfp)
>>> +{
>>> + return __iommu_alloc_pages(gfp, 0);
>>> +}
>>> +
>>> +/**
>>> + * __iommu_free_pages - free page of a given order
>>> + * @pages: head struct page of the page
>>
>> I think "pages" implies more than one page, this is just a (potentially
>> compound) page?
>
> Yes, more than one page, basically, when order may be > 0.
>
>>> +/**
>>> + * iommu_free_page - free page
>>> + * @virt: virtual address of the page to be freed.
>>> + */
>>> +static inline void iommu_free_page(void *virt)
>>> +{
>>> + iommu_free_pages(virt, 0);
>>> +}
>>> +
>>> +/**
>>> + * iommu_free_pages_list - free a list of pages.
>>> + * @pages: the head of the lru list to be freed.
>>
>> Document the locking requirements for this?
>
> Thank you for the review. I will add info about locking requirements,
> in fact they are very relaxed.
>
> These pages are added to the list by unmaps or remaps operation in
> Intel IOMMU implementation. These calls assume that whoever is doing
> those operations has exclusive access to the VA range in the page
> table of that operation. The pages in this freelist only belong to the
> former page-tables from the IOVA range for those operations.

These pages maybe be accessed concurrently by thread contexts other than
the IOMMU driver (such as debugfs).

Thanks,
Jingqi
>
>>> + */
>>> +static inline void iommu_free_pages_list(struct list_head *pages)
>>> +{
>>> + while (!list_empty(pages)) {
>>> + struct page *p = list_entry(pages->prev, struct page, lru);
>>> +
>>> + list_del(&p->lru);
>>> + put_page(p);
>>> + }
>>> +}