linux-kernel - Re: [RFC PATCH 00/18] Try to free user PTE page table pages

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Date:   Thu, 19 May 2022 12:03:41 +0800
From:   Qi Zheng <zhengqi.arch@...edance.com>
To:     Matthew Wilcox <willy@...radead.org>,
        David Hildenbrand <david@...hat.com>
Cc:     linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, songmuchun@...edance.com,
        zhouchengming@...edance.com, akpm@...ux-foundation.org,
        tglx@...utronix.de, kirill.shutemov@...ux.intel.com,
        jgg@...dia.com, tj@...nel.org, dennis@...nel.org,
        ming.lei@...hat.com
Subject: Re: [RFC PATCH 00/18] Try to free user PTE page table pages



On 2022/5/18 10:56 PM, Matthew Wilcox wrote:
> On Wed, May 18, 2022 at 04:51:06PM +0200, David Hildenbrand wrote:
>> yes, I talked about the involved challenges, especially, how malicious
>> user space can trigger allocation of almost elusively page tables and
>> essentially consume a lot of unmovable+unswappable memory and even store
>> secrets in the page table structure.
> 
> There are a lot of ways for userspace to consume a large amount of
> kernel memory.  For example, one can open a file and set file locks on

Yes, malicious programs are really hard to avoid, maybe we should try to
solve some common cases first (such as empty PTE tables).

> alternate bytes.  We generally handle this by accounting the memory to
> the process and let the OOM killer, rlimits, memcg or other mechanism
> take care of it.  Just because page tables are (generally) reclaimable
> doesn't mean we need to treat them specially.
> 

-- 
Thanks,
Qi