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

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Message-ID: <CAMj1kXGhwXsVrjqSMCzkQ83MWh0W=63x5_+fyuugyewkB=xAXw@mail.gmail.com>
Date:   Tue, 4 May 2021 12:28:35 +0200
From:   Ard Biesheuvel <ardb@...nel.org>
To:     Nikita Ermakov <arei@...linux.org>
Cc:     linux-efi <linux-efi@...r.kernel.org>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Atish Patra <atish.patra@....com>,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] RISC-V: Relocate the kernel relative to a DRAM base.

On Wed, 28 Apr 2021 at 18:00, Nikita Ermakov <arei@...linux.org> wrote:
>
> On Tue, 27 Apr 2021 at 15:43, Ard Biesheuvel <ardb@...nel.org> wrote:
> >
> > On Tue, 27 Apr 2021 at 14:07, Nikita Ermakov <arei@...linux.org> wrote:
> > >
> > > 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.