Re: [PATCH] RISC-V: Relocate the kernel relative to a DRAM base.

On Wed, 28 Apr 2021 at 18:00, Nikita Ermakov [off-list ref] wrote:

On Tue, 27 Apr 2021 at 15:43, Ard Biesheuvel [off-list ref] wrote:

quoted

On Tue, 27 Apr 2021 at 14:07, Nikita Ermakov [off-list ref] wrote:

quoted

Try to get the base of the DRAM from a DTB to use it as a lowest address
in physical memory to relocate the kernel. If it is not possible to
obtain the base from a /memory node of the DTB let's make an assumption
that the DRAM base at the beginning of the memory.

Why?

You right, this patch is useless. I made it because I overlooked
efi_low_alloc_above() in libstub/relocate.c
Sorry for bothering.

I had an issue with booting a Linux kernel with EFI stub on a HiFive
Unleashed board.
My boot chain was as follows: ZSBL -> FSBL -> OpenSBI -> U-Boot
(bootefi) -> Linux
When I tried to boot the kernel, U-Boot throws an Store/AMO access
fault exception.
I checked the riscv-stub.c and libstub/relocate.c and I thought that
it tries to relocate the kernel at the 2 MiB.
With this patch the kernel started to boot and I thought that the
theory was right.
But, after further investigation I found out that U-Boot EFI does not
mark the first 4 KiB page of DRAM as EFI_BOOT_SERVICE_DATA on the
board and efi_low_alloc_above() allocates this region as conventional
memory. The lowest region of DRAM is protected and that is why I got
the exception when the kernel tries to relocate to the 0x80000000. The
reason why U-Boot EFI does not mark the first 4 KiB of DRAM as
EFI_BOOT_SERVICE_DATA was that there wasn't /reserved-memory node in a
DTB. I had the FSBL with a patch which enables an entire L2 cache and
it does not preserve a0, a1 registers before a jump to the OpenSBI.
So, OpenSBI didn't fixup the DTB where it adds the /reserved-memory
node.

OK, thanks for the explanation. I will disregard this patch then.