linux-kernel - Re: [PATCH 0/4] Fix type confusion in page_table

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Message-ID: <zwixiok55avpjvfiknp7tzm7e4aragjj43a46abna4qqegdvdx@suat6sk34lgb>
Date:   Fri, 12 May 2023 00:19:09 +0800
From:   Ruihan Li <lrh2000@....edu.cn>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        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>,
        Ruihan Li <lrh2000@....edu.cn>
Subject: Re: [PATCH 0/4] Fix type confusion in page_table_check

On Thu, May 11, 2023 at 08:32:01AM -0700, Christoph Hellwig wrote:
> On Thu, May 11, 2023 at 09:44:55PM +0800, Ruihan Li wrote:
> > Christoph's patch perfectly fixes _one_ problem: kmalloc'ed memory
> > cannot be mapped to user space. However, as I detailed in the commit
> > message, this series of patches fixes _three_ problems.
> 
> FYI, I agree with you.  My simple patch was sent before reading
> your new series, and is a strict subset of it.

Thank you for the clarification.

> > I have to say that the original code is quite buggy. In the
> > gen_pool_dma_alloc path, there is no guarantee of page alignment. 
> 
> I also find this whole interface very problematic to start with,
> but that's a separate discussion for later.

Yes. I don't think hybrid allocation of DMA memory and normal memory in
one function is a good thing, but currently there is no clear way to fix
this. Mixing memory allocation and page allocation is another bad thing,
and at least, my patch can (hopefully) solve the second (and much
easier) issue.

Thanks,
Ruihan Li