Re: [PATCH 11/12] efi/loongarch: libstub: remove dependency on flattened DT

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On Mon, Sep 19, 2022 at 7:21 PM Ard Biesheuvel <ardb@xxxxxxxxxx> wrote:
>
> On Mon, 19 Sept 2022 at 13:15, Huacai Chen <chenhuacai@xxxxxxxxxx> wrote:
> >
> > On Mon, Sep 19, 2022 at 6:49 PM Ard Biesheuvel <ardb@xxxxxxxxxx> wrote:
> > >
> > > On Mon, 19 Sept 2022 at 12:47, Huacai Chen <chenhuacai@xxxxxxxxxx> wrote:
> > > >
> > > > On Mon, Sep 19, 2022 at 6:37 PM Ard Biesheuvel <ardb@xxxxxxxxxx> wrote:
> > > > >
> > > > > On Mon, 19 Sept 2022 at 12:33, Huacai Chen <chenhuacai@xxxxxxxxxx> wrote:
> > > > > >
> > > > > > Hi, Ard,
> > > > > >
> > > > > > On Mon, Sep 19, 2022 at 2:22 PM Ard Biesheuvel <ardb@xxxxxxxxxx> wrote:
> > > > > > >
> > > > > > > On Mon, 19 Sept 2022 at 08:06, Huacai Chen <chenhuacai@xxxxxxxxxx> wrote:
> > > > > > > >
> > > > > > > >  Hi, Ard,
> > > > > > > >
> > > > > > > > On Mon, Sep 19, 2022 at 1:15 PM Ard Biesheuvel <ardb@xxxxxxxxxx> wrote:
> > > > > > > > >
> > > > > > > > > On Mon, 19 Sept 2022 at 03:58, Huacai Chen <chenhuacai@xxxxxxxxxx> wrote:
> > > > > > > > > >
> > > > > > > > > > Hi, Ard,
> > > > > > > > > >
> > > > > > > > > > I think the parameters passed to the core kernel need to be discussed.
> > > > > > > > > > The old way (so-called old world):
> > > > > > > > > > a0=argc, a1=argv, a1=bpi
> > > > > > > > > >
> > > > > > > > > > The current way (so-called new world):
> > > > > > > > > > a0=efi boot flag, a1=fdt pointer
> > > > > > > > > >
> > > > > > > > > > The new way (in this patchset):
> > > > > > > > > > a0=efi boot flag, a1=systemtable, a2=cmdline
> > > > > > > > > >
> > > > > > > > > > I prefer to use the current way, there are 3 reasons:
> > > > > > > > > > 1, both acpi system and dt system can use the same parameters passing method;
> > > > > > > > >
> > > > > > > > > DT systems will use this too. The distinction is between EFI boot and
> > > > > > > > > non-EFI boot. We *really* should keep these separate, given the
> > > > > > > > > experience on ARM, where other projects invent ways to pass those
> > > > > > > > > values to the kernel without going through the stub.
> > > > > > > > In the last patch I see:
> > > > > > > > +               void *fdt_ptr = early_memremap_ro(fw_arg1, SZ_64K);
> > > > > > > > +
> > > > > > > > +               early_init_dt_scan(fdt_ptr);
> > > > > > > > +               early_init_fdt_reserve_self();
> > > > > > > > +
> > > > > > > >                 clear_bit(EFI_BOOT, &efi.flags);
> > > > > > > > So I suppose for the DT system that means a0=efi boot flag, a1=fdt
> > > > > > > > pointer, a2=cmdline? Then it is not exactly the same as the ACPI
> > > > > > > > system, but similar.
> > > > > > > >
> > > > > > >
> > > > > > > No, for non-EFI DT boot, the command line is passed via the DT, so
> > > > > > > a0=0x0 (non-efi), a1=DT, a2=0x0
> > > > > > >
> > > > > > > Do you intend to support non-EFI DT boot by the way?
> > > > > > I think we needn't support non-EFI DT boot, so a0=efi boot flag,
> > > > > > a1=systemtable, a2=cmdline is just OK (or maybe we can exchange a1/a2,
> > > > > > which looks similar to the old-world).
> > > > >
> > > > > Excellent. If non-EFI boot is not supported, we can drop the code that
> > > > > deals with that.
> > > > >
> > > > > > But I have another question: is
> > > > > > it early enough to get DT from systemtable for DT boot (in the current
> > > > > > way DT is the earliest thing)?
> > > > > >
> > > > >
> > > > > If you rely on DT only for the hardware description, then loading it
> > > > > from efi_init() should be fine.
> > > > OK, then please drop patch #12 at this time. It can be added when we
> > > > add Loongson-2K support.
> > > >
> > >
> > > OK
> > >
> > > > > > > I don't think it makes sense to allow efi=novamap on LoongArch, given
> > > > > > > that we cannot make use of the runtime services that way. So in my
> > > > > > > code, efi_novamap is set to false unconditionally.
> > > > > > Emm, I prefer to support "efi=novamap", the core kernel has already
> > > > > > supported "noefi" to disable runtime, I don't want to hack
> > > > > > efi_novamap. So please keep the efi boot flag, thanks.
> > > > > >
> > > > >
> > > > > Fair enough. Do you have any uses for efi_novamap in mind?
> > > > I usually use "efi=novamap" in EFI shell to see whether it can work
> > > > well without runtime. And I think I will modify this patch these days
> > > > because in another thread you said that this series cannot boot.
> > >
> > > It works fine now.
> > >
> > > However, clearing the EFI_BOOT flag is not the correct way to disable
> > > runtime services only. And note that we also have efi=noruntime - does
> > > that currently work on LoongArch?
> > OK, but we don't need to add a new "efi=noruntime" parameter, I can
> > use "noefi" instead.
>
> OK
>
> > But I think support "efi=novamap" is not a bad
> > idea (maybe I misunderstood its usage).
> >
>
> It basically exists to deal with broken EFI firmware on ARM laptops
> that were only intended to run Windows. Windows calls
> SetVirtualAddressMap() *after* creating the new mappings, and some
> broken firmware drivers will access those regions too early.
>
> On Linux, we install the mapping first, and then much later, we
> actually create the mappings and only activate them on a single CPU
> while the EFI runtime service call is in progress.
>
> In any case, I will reinstate the efi_novamap logic for now - we can
> always revisit it later.
OK, now I think there are no big problems. Only some bikesheddings:
1, Please use "a0=efi boot flag, a1=cmdline a2=systemtable" to pass
boot information, it looks most similar to the old-world, and we can
distinguish old-world/new-world by judging whether a0 is greater than
1.
2, I prefer "early return" in efi_init, i.e., if (boot_memmap ==
EFI_INVALID_TABLE_ADDR) then return immediately, this makes
indentation look better.
3, Declare "cmdline" out of the if() condition in init_environ() looks better.
4, I prefer "kernel_addr" rather than "image_addr" in efi_boot_kernel().
5, It seems that one line is enough for the last statement in efi_boot_kernel().

Hope this series will be stable as soon as possible, our kexec/kdump
work needs to adjust because of this change. :)

Huacai

>



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