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

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

On Tue, Feb 6, 2024 at 2:32 PM Laszlo Ersek <lersek@redhat.com> wrote:
>
> On 2/6/24 03:57, Chao Li wrote:
> > Hi Pedro, Laszlo,
> >
> > I have double-check this patch and I'd like to point out the following:
> >
> > 1. Some of the code in this patch actually refers to the Linux kernel.
> > But only used the name of kernel code , such as PUD, PMD, PTE, Swapper
> > Page Dir, etc.
> >
> > 2. Refer to the LoongArch TLB rules, if we use the multi-level page
> > table to search and filling, the usual logic is as follows:
> >
> >     a. Get the first level page table, called PGD, in reigster PGDL or PGDH.
> >
> >     b. PGD will index the 2st Dir, and the 2st Dir will index the 3st
> > Dir, and so on.
> >
> >     c. We would like to use the four-level page table, because if we use
> > two- or three-level page tables, the page tables will larger and must be
> > continuous, so we think the four-level is better(Linux kernel also uses
> > the four-level page tables).
> >
> >     d. LoongArch paging logic is shown in the image below(URL:
> > https://loongson.github.io/LoongArch-Documentation/LoongArch-Vol1-EN.html#memory-management-of-page-table-mapping):
> >
> > Referring to the above, should I use the old logic, rewrite the Linux
> > kernel-like code to EFI style and clean up some unused code and redesign
> > the PEI library, it that OK?
>
> I don't like the expression "rewrite the Linux kernel-like code to EFI
> style".
>
> You should not start with, or incorporate, anything that comes from
> Linux. Whatever you do, make sure it is not a derivative of Linux. Don't
> *derive* your edk2 contribution from Linux code.
>
> I think you are fine to implement any paging logic you prefer, as long
> as you start with an empty source file, and consult only the public
> LoongArch architecture specs, plus the rest of edk2 while writing the code.
>
> Consider the current source files from this patch "tainted". I don't
> encourage a piecemeal approach on this, "replace this", "rewrite that".
> The files look like they are a derivative of Linux code, so any further
> modifications in these files will just result in more derived code.
> Let's not play "where does this line come from" games. Scrap it all;
> implement it again from the ground up, using only the public arch specs.
>
> Just my opinion.
> Laszlo

I completely agree. Note that (AFAIK) you can also consult other
*license-compatible* code (BSD licenses, MIT, ISC, whatever).

-- 
Pedro


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