From: Song Liu <song@kernel.org>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: bpf@vger.kernel.org, linux-mm@kvack.org, peterz@infradead.org,
akpm@linux-foundation.org, x86@kernel.org, hch@lst.de,
rick.p.edgecombe@intel.com, aaron.lu@intel.com, rppt@kernel.org,
mcgrof@kernel.org
Subject: Re: [PATCH bpf-next v2 0/5] execmem_alloc for BPF programs
Date: Fri, 2 Dec 2022 00:38:45 -0800 [thread overview]
Message-ID: <CAPhsuW592J1+Z1e_g_1YPn9KcyX65WFfbbBx6hjyuj0wgN4_XQ@mail.gmail.com> (raw)
In-Reply-To: <87k03ar3e3.ffs@tglx>
Hi Thomas,
Thanks for all these suggestions!
On Thu, Dec 1, 2022 at 5:38 PM Thomas Gleixner <tglx@linutronix.de> wrote:
>
[...] (everything snipped here makes perfect sense).
>
> You have to be aware, that the rodata space needs to be page granular
> while text and data can really aggregate below the page alignment, but
> again might have different alignment requirements.
I don't quite follow why rodata space needs to be page granular. If text can
go below page granular, rodata should also do that, no?
>
> So you need a configuration mechanism which allows to specify per type:
>
> - Initial mapping type (RX, RWX, RW)
> - Alignment
> - Granularity
> - Address space restrictions
[...]
>
> Step 1:
>
These steps are really helpful. Thanks!
[...]
>
> For text that's obviously module_write_text(), but for the [ro]data
> mappings memcpy() is still fine. For the rodata mapping you need
> set_memory_ro() right in the module prepare stage and for the
> ro_after_init_data() you do that after the module init function returns
> success, which is pretty much what the code does today.
I guess this is related to rodata needs to be page granular? But I
don't think I got the idea. Do we allow rodata and rwdata share the
same 2MB page? ro_after_init_data seems trickier.
>
> Step 5:
>
[...]
>
> Linus once said:
>
> "Bad programmers worry about the code. Good programmers worry about
> data structures and their relationships."
>
> He's absolutely right. Here is my version of it:
>
> The order of things to worry about:
>
> 1) Problem analysis
> 2) Concepts
> 3) Data structures and their relationships
> 4) Code
>
> #1 You need to understand the problem fully to come up with
> concepts
>
> #2 Once you understand the problem fully you can talk about
> concepts to solve it
>
> #3 Maps the concept to data structures and forms relationships
>
> #4 Is the logical consequence of #1 + #2 + #3 and because your
> concept makes sense, the data structures and their
> relationships are understandable, the code becomes
> understandable too.
>
> If any of the steps finds a gap in the previous ones, then you
> have to go back and solve those first.
>
> Any attempt to reorder the above is putting the cart before the horse
> and a guarantee for failure.
Thanks for these advices! They would help me for many years.
>
> Now go back and carefully read up on what I wrote above and in my
> previous mail.
>
> The previous mail was mostly about #1 to explain the problem as broad as
> possible and an initial stab at #2 suggesting concepts to solve it.
>
> This one is still covering some aspects of #1, but it is mostly about #2
> and more focussed on particular aspects of the concept. If you look at
> it carefully then you find some bits which map to #3 but still at the
> conceptual level.
>
> Did I talk about code or implementation details?
>
> Not at all and I'm not going to do so before #1 and #2 are agreed
> on. The above pseudo code snippets are just for illustration and I used
> them because I was too lazy to write a novel, but they all are still at
> the conceptual level.
>
> Now you can rightfully argue that if you stich those snippets together
> then they form a picture which outlines the implementation, but that's
> the whole purpose of this exercise, right?
I guess I will do my homework, and come back with as much information
as possible for #1 + #2 + #3. Then, we can discuss whether it makes
sense at all.
Does this sound like the right approach?
Thanks,
Song
next prev parent reply other threads:[~2022-12-02 8:39 UTC|newest]
Thread overview: 91+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-11-07 22:39 [PATCH bpf-next v2 0/5] execmem_alloc for BPF programs Song Liu
2022-11-07 22:39 ` [PATCH bpf-next v2 1/5] vmalloc: introduce execmem_alloc, execmem_free, and execmem_fill Song Liu
2022-11-07 22:39 ` [PATCH bpf-next v2 2/5] x86/alternative: support execmem_alloc() and execmem_free() Song Liu
2022-11-07 22:39 ` [PATCH bpf-next v2 3/5] bpf: use execmem_alloc for bpf program and bpf dispatcher Song Liu
2022-11-07 22:39 ` [PATCH bpf-next v2 4/5] vmalloc: introduce register_text_tail_vm() Song Liu
2022-11-07 22:39 ` [PATCH bpf-next v2 5/5] x86: use register_text_tail_vm Song Liu
2022-11-08 19:04 ` Edgecombe, Rick P
2022-11-08 22:15 ` Song Liu
2022-11-15 17:28 ` Edgecombe, Rick P
2022-11-07 22:55 ` [PATCH bpf-next v2 0/5] execmem_alloc for BPF programs Luis Chamberlain
2022-11-07 23:13 ` Song Liu
2022-11-07 23:39 ` Luis Chamberlain
2022-11-08 0:13 ` Edgecombe, Rick P
2022-11-08 2:45 ` Luis Chamberlain
2022-11-08 18:20 ` Song Liu
2022-11-08 18:12 ` Song Liu
2022-11-08 11:27 ` Mike Rapoport
2022-11-08 12:38 ` Aaron Lu
2022-11-09 6:55 ` Christoph Hellwig
2022-11-09 11:05 ` Peter Zijlstra
2022-11-08 16:51 ` Edgecombe, Rick P
2022-11-08 18:50 ` Song Liu
2022-11-09 11:17 ` Mike Rapoport
2022-11-09 17:04 ` Edgecombe, Rick P
2022-11-09 17:53 ` Song Liu
2022-11-13 10:34 ` Mike Rapoport
2022-11-14 20:30 ` Song Liu
2022-11-15 21:18 ` Luis Chamberlain
2022-11-15 21:39 ` Edgecombe, Rick P
2022-11-16 22:34 ` Luis Chamberlain
2022-11-17 8:50 ` Mike Rapoport
2022-11-17 18:36 ` Song Liu
2022-11-20 10:41 ` Mike Rapoport
2022-11-21 14:52 ` Song Liu
2022-11-30 9:39 ` Mike Rapoport
2022-11-09 17:43 ` Song Liu
2022-11-09 21:23 ` Christophe Leroy
2022-11-10 1:50 ` Song Liu
2022-11-13 10:42 ` Mike Rapoport
2022-11-14 20:45 ` Song Liu
2022-11-15 20:51 ` Luis Chamberlain
2022-11-20 10:44 ` Mike Rapoport
2022-11-08 18:41 ` Song Liu
2022-11-08 19:43 ` Christophe Leroy
2022-11-08 21:40 ` Song Liu
2022-11-13 9:58 ` Mike Rapoport
2022-11-14 20:13 ` Song Liu
2022-11-08 11:44 ` Christophe Leroy
2022-11-08 18:47 ` Song Liu
2022-11-08 19:32 ` Christophe Leroy
2022-11-08 11:48 ` Mike Rapoport
2022-11-15 1:30 ` Song Liu
2022-11-15 17:34 ` Edgecombe, Rick P
2022-11-15 21:54 ` Song Liu
2022-11-15 22:14 ` Edgecombe, Rick P
2022-11-15 22:32 ` Song Liu
2022-11-16 1:20 ` Song Liu
2022-11-16 21:22 ` Edgecombe, Rick P
2022-11-16 22:03 ` Song Liu
2022-11-15 21:09 ` Luis Chamberlain
2022-11-15 21:32 ` Luis Chamberlain
2022-11-15 22:48 ` Song Liu
2022-11-16 22:33 ` Luis Chamberlain
2022-11-16 22:47 ` Edgecombe, Rick P
2022-11-16 23:53 ` Luis Chamberlain
2022-11-17 1:17 ` Song Liu
2022-11-17 9:37 ` Mike Rapoport
2022-11-29 10:23 ` Thomas Gleixner
2022-11-29 17:26 ` Song Liu
2022-11-29 23:56 ` Thomas Gleixner
2022-11-30 16:18 ` Song Liu
2022-12-01 9:08 ` Thomas Gleixner
2022-12-01 19:31 ` Song Liu
2022-12-02 1:38 ` Thomas Gleixner
2022-12-02 8:38 ` Song Liu [this message]
2022-12-02 9:22 ` Thomas Gleixner
2022-12-06 20:25 ` Song Liu
2022-12-07 15:36 ` Thomas Gleixner
2022-12-07 16:53 ` Christophe Leroy
2022-12-07 19:29 ` Song Liu
2022-12-07 21:04 ` Thomas Gleixner
2022-12-07 21:48 ` Christophe Leroy
2022-12-07 19:26 ` Song Liu
2022-12-07 20:57 ` Thomas Gleixner
2022-12-07 23:17 ` Song Liu
2022-12-02 10:46 ` Christophe Leroy
2022-12-02 17:43 ` Thomas Gleixner
2022-12-01 20:23 ` Mike Rapoport
2022-12-01 22:34 ` Thomas Gleixner
2022-12-03 14:46 ` Mike Rapoport
2022-12-03 20:58 ` Thomas Gleixner
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