Re: [edk2-devel] [PATCH v8 14/37] UefiCpuPkg: Add CpuMmuLib to UefiCpuPkg

["Pedro Falcato" <pedro.falcato@gmail.com>]

On Wed, Jan 31, 2024 at 1:41 PM Laszlo Ersek <lersek@redhat.com> wrote:
>
> Hi Pedro,
>
> On 1/31/24 11:33, Pedro Falcato wrote:
> > On Fri, Jan 26, 2024 at 6:29 AM Chao Li <lichao@loongson.cn> wrote:
> >>
> >> Add a new library named CpuMmuLib and add a LoongArch64 instance with in
> >> the library.
> >> It provides two-stage MMU libraryinstances, PEI and DXE.
> >>
> >> BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=4584
> >> [...]
> >> diff --git a/UefiCpuPkg/Library/CpuMmuLib/LoongArch64/CommonMmuLib.c b/UefiCpuPkg/Library/CpuMmuLib/LoongArch64/CommonMmuLib.c
> >> new file mode 100644
> >> index 0000000000..2e852c3371
> >> --- /dev/null
> >> +++ b/UefiCpuPkg/Library/CpuMmuLib/LoongArch64/CommonMmuLib.c
> >> @@ -0,0 +1,988 @@
> >> +/** @file
> >> +
> >> +  CPU Memory Map Unit Handler Library common functions.
> >> +
> >> +  Copyright (c) 2024 Loongson Technology Corporation Limited. All rights reserved.<BR>
> >> +
> >> +  SPDX-License-Identifier: BSD-2-Clause-Patent
> >> +
> >> +  @par Glossary:
> >> +    - Pgd or Pgd or PGD    - Page Global Directory
> >> +    - Pud or Pud or PUD    - Page Upper Directory
> >> +    - Pmd or Pmd or PMD    - Page Middle Directory
> >> +    - Pte or pte or PTE    - Page Table Entry
> >> +    - Val or VAL or val    - Value
> >> +    - Dir    - Directory
> >> +**/
> >
> > You took essentially Linux code [...] and EDK2-ify'd it. Congrats,
> > this is cursed.
>
> are you saying this patch is effectively a port of GPL'd Linux code
> (potentially *old* code, but still), with the GPL simply replaced with
> BSD-2-Clause-Patent?

Yes. With a bit of patience, you can get a good idea of the
similarities by kernel-ifying identifiers and searching them on
https://elixir.bootlin.com/linux/latest/source.
The smoking gun being the types and strategy used for the MMU code
(PGD, P4D, PUD, PMD, PTE and VAL/PTEVAL being a very unique linux
strategy that is not emulated elsewhere AFAIK) and SWAP_PAGE_DIR (->
swapper_pg_dir, the kernel's pgd; swap has no meaning whatsoever in
UEFI land).

>
> That sounds... shocking. If such a patch were merged into edk2, it would
> violate both the GPL (the GPL cannot just be "relaxed") and the edk2
> rules (edk2 does not want GPL code).
>
> The only exception would be if Loongson Technology Corporation Limited
> were the Copyright holder of the Linux code, and this patch were a
> relicensing. But then that too would have to be documented, IMO.

FWIW, I wasn't objecting to the patch on legal grounds, but mainly
technical ones, since I was assuming Loongson had written most of this
code.
However (arch/loongarch/include/asm/pgtable.h):
/* SPDX-License-Identifier: GPL-2.0 */
/*
 * Copyright (C) 2020-2022 Loongson Technology Corporation Limited
 *
 * Derived from MIPS:
 * Copyright (C) 1994, 95, 96, 97, 98, 99, 2000, 2003 Ralf Baechle
 * Copyright (C) 1999, 2000, 2001 Silicon Graphics, Inc.
 */

and after a closer look, other functions such as P*AllocGet()
mirroring p4d_alloc, pud_alloc and pmd_alloc (from include/linux/mm.h,
definitely not loongson's copyright) very closely, it seems like this
patch is a walking copyright violation.
Not that implementing something similar to Linux's is impossible in a
clean-room instance, but the code used and the patterns used imitate
Linux's down to a t.

-- 
Pedro


-=-=-=-=-=-=-=-=-=-=-=-
Groups.io Links: You receive all messages sent to this group.
View/Reply Online (#114911): https://edk2.groups.io/g/devel/message/114911
Mute This Topic: https://groups.io/mt/103971653/7686176
Group Owner: devel+owner@edk2.groups.io
Unsubscribe: https://edk2.groups.io/g/devel/unsub [rebecca@openfw.io]
-=-=-=-=-=-=-=-=-=-=-=-