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SubjectRe: [PATCH 1/1] efi/libstub: DRAM base calculation
On Mon, 7 Sep 2020 at 11:31, Heinrich Schuchardt <xypron.glpk@gmx.de> wrote:
>
> On 07.09.20 09:00, Maxim Uvarov wrote:
> > On Fri, 4 Sep 2020 at 18:50, Heinrich Schuchardt <xypron.glpk@gmx.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@gmx.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
> >>
>

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