linux-kernel - Re: [PATCH v2 1/4] usb: usbfs: Enforce page requirements for mmap

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Date:   Tue, 16 May 2023 23:22:56 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Ruihan Li <lrh2000@....edu.cn>
Cc:     linux-mm@...ck.org, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Pasha Tatashin <pasha.tatashin@...een.com>,
        David Hildenbrand <david@...hat.com>,
        Matthew Wilcox <willy@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Christoph Hellwig <hch@...radead.org>,
        Alan Stern <stern@...land.harvard.edu>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        syzbot+fcf1a817ceb50935ce99@...kaller.appspotmail.comm,
        stable@...r.kernel.org
Subject: Re: [PATCH v2 1/4] usb: usbfs: Enforce page requirements for mmap

On Mon, May 15, 2023 at 09:09:55PM +0800, Ruihan Li wrote:
> To address these issues, this patch introduces hcd_alloc_coherent_pages,
> which addresses the above two problems. Specifically,
> hcd_alloc_coherent_pages uses gen_pool_dma_alloc_align instead of
> gen_pool_dma_alloc to ensure that the memory is page-aligned. To replace
> kmalloc, hcd_alloc_coherent_pages directly allocates pages by calling
> __get_free_pages.

This looks reasonable in that it fixes the bug.  But I really don't
like how it makes the mess of USB allocation APIs even messier :P

Not really your faul, but someone really needs to look into the usb
memory allocators and DMA mapping, which is tied to that and just as
bad.