linux-kernel - Re: [PATCH 1/1] efi/libstub: DRAM base calculation

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Message-ID: <CAD8XO3YGKwqbt6cYZQgauioeywLFg56tm+PFM6_nGhuJwSk4Jg@mail.gmail.com>
Date:   Mon, 7 Sep 2020 13:21:43 +0300
From:   Maxim Uvarov <maxim.uvarov@...aro.org>
To:     Heinrich Schuchardt <xypron.glpk@....de>
Cc:     Ard Biesheuvel <ardb@...nel.org>, Ingo Molnar <mingo@...nel.org>,
        Arvind Sankar <nivedita@...m.mit.edu>,
        linux-efi@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Jens Wiklander <jens.wiklander@...aro.org>,
        Ilias Apalodimas <ilias.apalodimas@...aro.org>
Subject: Re: [PATCH 1/1] efi/libstub: DRAM base calculation

On Mon, 7 Sep 2020 at 11:31, Heinrich Schuchardt <xypron.glpk@....de> wrote:
>
> On 07.09.20 09:00, Maxim Uvarov wrote:
> > On Fri, 4 Sep 2020 at 18:50, Heinrich Schuchardt <xypron.glpk@....de> wrote:
> >>
> >> In the memory map the regions with the lowest addresses may be of type
> >> EFI_RESERVED_TYPE. The reserved areas may be discontinuous relative to the
> >> rest of the memory. So for calculating the maximum loading address for the
> >> device tree and the initial ramdisk image these reserved areas should not
> >> be taken into account.
> >>
> >> Signed-off-by: Heinrich Schuchardt <xypron.glpk@....de>
> >> ---
> >>  drivers/firmware/efi/libstub/efi-stub.c | 3 ++-
> >>  1 file changed, 2 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/drivers/firmware/efi/libstub/efi-stub.c b/drivers/firmware/efi/libstub/efi-stub.c
> >> index c2484bf75c5d..13058ac75765 100644
> >> --- a/drivers/firmware/efi/libstub/efi-stub.c
> >> +++ b/drivers/firmware/efi/libstub/efi-stub.c
> >> @@ -106,7 +106,8 @@ static unsigned long get_dram_base(void)
> >>         map.map_end = map.map + map_size;
> >>
> >>         for_each_efi_memory_desc_in_map(&map, md) {
> >> -               if (md->attribute & EFI_MEMORY_WB) {
> >> +               if (md->attribute & EFI_MEMORY_WB &&
> >> +                   md->type != EFI_RESERVED_TYPE) {
> >
> > shouldn't the type here be CONVENTIONAL?
>
> In 32bit ARM reserve_kernel_base() the following are considered:
>
> * EFI_LOADER_CODE
> * EFI_LOADER_DATA
> * EFI_BOOT_SERVICES_CODE
> * EFI_BOOT_SERVICES_DATA
> * EFI_CONVENTIONAL_MEMORY
>
> What I have not yet fully understood is why Linux on ARM 32bit tries to
> put the kernel into the first 128 MiB. Cf. handle_kernel_image() in
> drivers/firmware/efi/libstub/arm32-stub.c.
>

Are you looking to the latest kernel?
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/firmware/efi/libstub/arm32-stub.c?h=v5.9-rc4#n211
efi_bs_call(allocate_pages,..) is only for EFI_CONVENTIONAL_MEMORY.

> According to the comments this is due to some implementation detail in
> the Linux zImage decompressor and not required by UEFI or the hardware:
>
>          Verify that the DRAM base address is compatible with the ARM
>          boot protocol, which determines the base of DRAM by masking
>          off the low 27 bits of the address at which the zImage is
>          loaded. These assumptions are made by the decompressor,
>          before any memory map is available.

I think that is also fixed with:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/drivers/firmware/efi/libstub/arm32-stub.c?h=v5.9-rc4&id=d0f9ca9be11f25ef4151195eab7ea36d136084f6

Maxim.

>
> Best regards
>
> Heinrich
>
> >
> >>                         if (membase > md->phys_addr)
> >>                                 membase = md->phys_addr;
> >>                 }
> >> --
> >> 2.28.0
> >>
>