linux-hardening - Re: [PATCH -next] mm: usercopy: add a debugfs interface to bypass the vmalloc check.

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Message-ID: <8462ee54-790a-f6fa-2145-f4b32ec9c4bd@huawei.com>
Date: Wed, 4 Dec 2024 09:38:15 +0800
From: zuoze <zuoze1@...wei.com>
To: Matthew Wilcox <willy@...radead.org>, Uladzislau Rezki <urezki@...il.com>
CC: Kefeng Wang <wangkefeng.wang@...wei.com>, <gustavoars@...nel.org>,
	<akpm@...ux-foundation.org>, <linux-hardening@...r.kernel.org>,
	<linux-mm@...ck.org>, <keescook@...omium.org>
Subject: Re: [PATCH -next] mm: usercopy: add a debugfs interface to bypass the
 vmalloc check.



在 2024/12/4 3:56, Matthew Wilcox 写道:
> On Tue, Dec 03, 2024 at 08:02:26PM +0100, Uladzislau Rezki wrote:
> 
> I think there are a few other things we can try here.
> 
> First, if the copy is small (and I still don't have an answer to that
> ...), we can skip the vmalloc lookup if the copy doesn't cross a page
> boundary.
> 

large data packet.

> Second, we could try storing this in a maple tree rather than an rbtree.
> That gives us RCU protected lookups rather than under a spinlock.
> 
> It might even be worth going to a rwlock first, in case the problem is
> that there's severe lock contention.
> 
> But I've asked for data on spinlock contention and not received an
> answer on that either, so I don't know what to suggest.

Thank you very much for your suggestions. We will check the spinlock
contention in the future.

> 
> Anyway, NACK to the original patch; that's just a horrible idea.
>