netdev - Re: [PATCH net-next v4 1/4] mm: add a signature in struct page

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [day] [month] [year] [list]
Message-ID: <8f815871-e384-3e65-56a8-39e379dea4ce@huawei.com>
Date:   Thu, 13 May 2021 11:25:22 +0800
From:   Yunsheng Lin <linyunsheng@...wei.com>
To:     Matthew Wilcox <willy@...radead.org>
CC:     Ilias Apalodimas <ilias.apalodimas@...aro.org>,
        Matteo Croce <mcroce@...ux.microsoft.com>,
        Networking <netdev@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>,
        Ayush Sawal <ayush.sawal@...lsio.com>,
        "Vinay Kumar Yadav" <vinay.yadav@...lsio.com>,
        Rohit Maheshwari <rohitm@...lsio.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        Marcin Wojtas <mw@...ihalf.com>,
        Russell King <linux@...linux.org.uk>,
        Mirko Lindner <mlindner@...vell.com>,
        Stephen Hemminger <stephen@...workplumber.org>,
        "Tariq Toukan" <tariqt@...dia.com>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        "Alexei Starovoitov" <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        "John Fastabend" <john.fastabend@...il.com>,
        Boris Pismenny <borisp@...dia.com>,
        Arnd Bergmann <arnd@...db.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Vlastimil Babka <vbabka@...e.cz>, Yu Zhao <yuzhao@...gle.com>,
        Will Deacon <will@...nel.org>,
        Michel Lespinasse <walken@...gle.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Roman Gushchin <guro@...com>, Hugh Dickins <hughd@...gle.com>,
        Peter Xu <peterx@...hat.com>, Jason Gunthorpe <jgg@...pe.ca>,
        Jonathan Lemon <jonathan.lemon@...il.com>,
        Alexander Lobakin <alobakin@...me>,
        Cong Wang <cong.wang@...edance.com>, wenxu <wenxu@...oud.cn>,
        Kevin Hao <haokexin@...il.com>,
        Jakub Sitnicki <jakub@...udflare.com>,
        Marco Elver <elver@...gle.com>,
        Willem de Bruijn <willemb@...gle.com>,
        Miaohe Lin <linmiaohe@...wei.com>,
        Guillaume Nault <gnault@...hat.com>,
        open list <linux-kernel@...r.kernel.org>,
        <linux-rdma@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        David Ahern <dsahern@...il.com>,
        Lorenzo Bianconi <lorenzo@...nel.org>,
        Saeed Mahameed <saeedm@...dia.com>,
        Andrew Lunn <andrew@...n.ch>, Paolo Abeni <pabeni@...hat.com>,
        Sven Auhagen <sven.auhagen@...eatech.de>
Subject: Re: [PATCH net-next v4 1/4] mm: add a signature in struct page

On 2021/5/13 10:35, Matthew Wilcox wrote:
> On Thu, May 13, 2021 at 10:15:26AM +0800, Yunsheng Lin wrote:
>> On 2021/5/12 23:57, Matthew Wilcox wrote:
>>> You'll need something like this because of the current use of
>>> page->index to mean "pfmemalloc".
>>>
>>> @@ -1682,12 +1684,12 @@ static inline bool page_is_pfmemalloc(const struct page *page)
>>>   */
>>>  static inline void set_page_pfmemalloc(struct page *page)
>>>  {
>>> -	page->index = -1UL;
>>> +	page->compound_head = 2;
>>
>> Is there any reason why not use "page->compound_head |= 2"? as
>> corresponding to the "page->compound_head & 2" in the above
>> page_is_pfmemalloc()?
>>
>> Also, this may mean we need to make sure to pass head page or
>> base page to set_page_pfmemalloc() if using
>> "page->compound_head = 2", because it clears the bit 0 and head
>> page ptr for tail page too, right?
> 
> I think what you're missing here is that this page is freshly allocated.
> This is information being passed from the page allocator to any user
> who cares to look at it.  By definition, it's set on the head/base page, and
> there is nothing else present in the page->compound_head.  Doing an OR
> is more expensive than just setting it to 2.

Thanks for clarifying.

> 
> I'm not really sure why set/clear page_pfmemalloc are defined in mm.h.
> They should probably be in mm/page_alloc.c where nobody else would ever
> think that they could or should be calling them.>
>>>  		struct {	/* page_pool used by netstack */
>>> -			/**
>>> -			 * @dma_addr: might require a 64-bit value on
>>> -			 * 32-bit architectures.
>>> -			 */
>>> +			unsigned long pp_magic;
>>> +			struct page_pool *pp;
>>> +			unsigned long _pp_mapping_pad;
>>>  			unsigned long dma_addr[2];
>>
>> It seems the dma_addr[1] aliases with page->private, and
>> page_private() is used in skb_copy_ubufs()?
>>
>> It seems we can avoid using page_private() in skb_copy_ubufs()
>> by using a dynamic allocated array to store the page ptr?
> 
> This is why I hate it when people use page_private() instead of
> documenting what they're doing in struct page.  There is no way to know
> (as an outsider to networking) whether the page in skb_copy_ubufs()
> comes from page_pool.  I looked at it, and thought it didn't:
> 
>                 page = alloc_page(gfp_mask);
> 
> but if you say those pages can come from page_pool, I believe you.

page_private() using in skb_copy_ubufs() does indeed seem ok here.
the page_private() is used on the page which is freshly allocated
from alloc_page().

Sorry for the confusion.

> 
> .
>