linux-kernel - Re: [RFC v2 0/4] vmalloc_exec for modules and BPF programs

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Message-ID: <E8A7DEAE-C1C6-4821-A3A3-FD4996414AFD@fb.com>
Date:   Mon, 17 Oct 2022 16:23:52 +0000
From:   Song Liu <songliubraving@...a.com>
To:     Christoph Hellwig <hch@....de>
CC:     Song Liu <song@...nel.org>, Linux-MM <linux-mm@...ck.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        X86 ML <x86@...nel.org>, Peter Zijlstra <peterz@...radead.org>,
        Kernel Team <Kernel-team@...com>,
        "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>,
        "Hansen, Dave" <dave.hansen@...el.com>,
        "urezki@...il.com" <urezki@...il.com>
Subject: Re: [RFC v2 0/4] vmalloc_exec for modules and BPF programs

Hi Chritoph, 

> On Oct 17, 2022, at 12:26 AM, Christoph Hellwig <hch@....de> wrote:
> 
> On Fri, Oct 07, 2022 at 04:43:11PM -0700, Song Liu wrote:
>> Changes RFC v1 => RFC v2:
>> 1. Major rewrite of the logic of vmalloc_exec and vfree_exec. They now
>>   work fine with BPF programs (patch 1, 2, 4). But module side (patch 3)
>>   still need some work.
> 
> Can you please move the changelog under the description of WTF the
> series actually does like the normal kernel process?  Explaining the
> changes from a previous version before you even describe what the series
> does is completely incoherent.

Will fix in the next version. 

> 
>> This set is a prototype that allows dynamic kernel text (modules, bpf
>> programs, various trampolines, etc.) to share huge pages. The idea is
>> similar to Peter's suggestion in [1]. Please refer to each patch for
>> more detais.
> 
> Well, nothing explains what the method is to avoid having memory
> that is mapped writable and executable at the same time, which really
> could use some explanation here (and in the main patch as well).

Thanks for the feedback. I will add this. 

Does the code look good to you? I personally think patch 1, 2, 4 could
ship with a little more work. 

Thanks,
Song