Re: [RFC PATCH 5/5] RISC-V: Add EFI stub support.

From: Anup Patel
Date: Tue Mar 10 2020 - 03:38:55 EST

On Tue, Mar 10, 2020 at 12:39 PM Atish Patra <atishp@xxxxxxxxxxxxxx> wrote:
>
> On Thu, Feb 27, 2020 at 10:57 PM Ard Biesheuvel <ardb@xxxxxxxxxx> wrote:
> >
> > On Fri, 28 Feb 2020 at 02:05, Atish Patra <Atish.Patra@xxxxxxx> wrote:
> > >
> > > On Thu, 2020-02-27 at 20:59 +0100, Ard Biesheuvel wrote:
> > > > On Thu, 27 Feb 2020 at 20:53, Atish Patra <Atish.Patra@xxxxxxx>
> > > > wrote:
> > > > > On Wed, 2020-02-26 at 08:28 +0100, Ard Biesheuvel wrote:
> > > > > > On Wed, 26 Feb 2020 at 02:10, Atish Patra <atish.patra@xxxxxxx>
> > > > > > wrote:
> > > > > > > Add a RISC-V architecture specific stub code that actually
> > > > > > > copies
> > > > > > > the
> > > > > > > actual kernel image to a valid address and jump to it after
> > > > > > > boot
> > > > > > > services
> > > > > > > are terminated. Enable UEFI related kernel configs as well for
> > > > > > > RISC-V.
> > > > > > >
> > > > > > > Signed-off-by: Atish Patra <atish.patra@xxxxxxx>
> > > > > > > ---
> > > > > > > arch/riscv/Kconfig | 20 ++++
> > > > > > > arch/riscv/Makefile | 1 +
> > > > > > > arch/riscv/configs/defconfig | 1 +
> > > > > > > drivers/firmware/efi/libstub/Makefile | 8 ++
> > > > > > > drivers/firmware/efi/libstub/riscv-stub.c | 135
> > > > > > > ++++++++++++++++++++++
> > > > > > > 5 files changed, 165 insertions(+)
> > > > > > > create mode 100644 drivers/firmware/efi/libstub/riscv-stub.c
> > > > > > >
> > > > > > > diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> > > > > > > index 42c122170cfd..68b1d565e51d 100644
> > > > > > > --- a/arch/riscv/Kconfig
> > > > > > > +++ b/arch/riscv/Kconfig
> > > > > > > @@ -372,10 +372,30 @@ config CMDLINE_FORCE
> > > > > > >
> > > > > > > endchoice
> > > > > > >
> > > > > > > +config EFI_STUB
> > > > > > > + bool
> > > > > > > +
> > > > > > > +config EFI
> > > > > > > + bool "UEFI runtime support"
> > > > > > > + depends on OF
> > > > > > > + select LIBFDT
> > > > > > > + select UCS2_STRING
> > > > > > > + select EFI_PARAMS_FROM_FDT
> > > > > > > + select EFI_STUB
> > > > > > > + select EFI_GENERIC_ARCH_STUB
> > > > > > > + default y
> > > > > > > + help
> > > > > > > + This option provides support for runtime services
> > > > > > > provided
> > > > > > > + by UEFI firmware (such as non-volatile variables,
> > > > > > > realtime
> > > > > > > + clock, and platform reset). A UEFI stub is also
> > > > > > > provided
> > > > > > > to
> > > > > > > + allow the kernel to be booted as an EFI application.
> > > > > > > This
> > > > > > > + is only useful on systems that have UEFI firmware.
> > > > > > > +
> > > > > > > endmenu
> > > > > > >
> > > > > > > menu "Power management options"
> > > > > > >
> > > > > > > source "kernel/power/Kconfig"
> > > > > > > +source "drivers/firmware/Kconfig"
> > > > > > >
> > > > > > > endmenu
> > > > > > > diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile
> > > > > > > index b9009a2fbaf5..0afaa89ba9ad 100644
> > > > > > > --- a/arch/riscv/Makefile
> > > > > > > +++ b/arch/riscv/Makefile
> > > > > > > @@ -78,6 +78,7 @@ head-y := arch/riscv/kernel/head.o
> > > > > > > core-y += arch/riscv/
> > > > > > >
> > > > > > > libs-y += arch/riscv/lib/
> > > > > > > +core-$(CONFIG_EFI_STUB) +=
> > > > > > > $(objtree)/drivers/firmware/efi/libstub/lib.a
> > > > > > >
> > > > > > > PHONY += vdso_install
> > > > > > > vdso_install:
> > > > > > > diff --git a/arch/riscv/configs/defconfig
> > > > > > > b/arch/riscv/configs/defconfig
> > > > > > > index e2ff95cb3390..0a5d3578f51e 100644
> > > > > > > --- a/arch/riscv/configs/defconfig
> > > > > > > +++ b/arch/riscv/configs/defconfig
> > > > > > > @@ -125,3 +125,4 @@ CONFIG_DEBUG_BLOCK_EXT_DEVT=y
> > > > > > > # CONFIG_FTRACE is not set
> > > > > > > # CONFIG_RUNTIME_TESTING_MENU is not set
> > > > > > > CONFIG_MEMTEST=y
> > > > > > > +CONFIG_EFI=y
> > > > > > > diff --git a/drivers/firmware/efi/libstub/Makefile
> > > > > > > b/drivers/firmware/efi/libstub/Makefile
> > > > > > > index 2c5b76787126..38facb61745b 100644
> > > > > > > --- a/drivers/firmware/efi/libstub/Makefile
> > > > > > > +++ b/drivers/firmware/efi/libstub/Makefile
> > > > > > > @@ -21,6 +21,8 @@ cflags-$(CONFIG_ARM64) :=
> > > > > > > $(subst
> > > > > > > $(CC_FLAGS_FTRACE),,$(KBUILD_CFLAGS)) \
> > > > > > > cflags-$(CONFIG_ARM) := $(subst
> > > > > > > $(CC_FLAGS_FTRACE),,$(KBUILD_CFLAGS)) \
> > > > > > > -fno-builtin -fpic \
> > > > > > > $(call cc-option,-mno-
> > > > > > > single-
> > > > > > > pic-base)
> > > > > > > +cflags-$(CONFIG_RISCV) := $(subst
> > > > > > > $(CC_FLAGS_FTRACE),,$(KBUILD_CFLAGS)) \
> > > > > > > + -fpic
> > > > > > >
> > > > > > > cflags-$(CONFIG_EFI_GENERIC_ARCH_STUB) +=
> > > > > > > -I$(srctree)/scripts/dtc/libfdt
> > > > > > >
> > > > > > > @@ -55,6 +57,7 @@ lib-
> > > > > > > $(CONFIG_EFI_GENERIC_ARCH_STUB) +=
> > > > > > > efi-stub.o fdt.o string.o \
> > > > > > > lib-$(CONFIG_ARM) += arm32-stub.o
> > > > > > > lib-$(CONFIG_ARM64) += arm64-stub.o
> > > > > > > lib-$(CONFIG_X86) += x86-stub.o
> > > > > > > +lib-$(CONFIG_RISCV) += riscv-stub.o
> > > > > > > CFLAGS_arm32-stub.o := -DTEXT_OFFSET=$(TEXT_OFFSET)
> > > > > > > CFLAGS_arm64-stub.o := -DTEXT_OFFSET=$(TEXT_OFFSET)
> > > > > > >
> > > > > > > @@ -79,6 +82,11 @@ STUBCOPY_FLAGS-$(CONFIG_ARM64) += --
> > > > > > > prefix-alloc-sections=.init \
> > > > > > > --prefix-symbols=__efistub_
> > > > > > > STUBCOPY_RELOC-$(CONFIG_ARM64) := R_AARCH64_ABS
> > > > > > >
> > > > > > > +STUBCOPY_FLAGS-$(CONFIG_RISCV) += --prefix-alloc-
> > > > > > > sections=.init \
> > > > > > > + --prefix-symbols=__efistub_
> > > > > > > +STUBCOPY_RELOC-$(CONFIG_RISCV) := R_RISCV_HI20
> > > > > > > +
> > > > > > > +
> > > > > > > $(obj)/%.stub.o: $(obj)/%.o FORCE
> > > > > > > $(call if_changed,stubcopy)
> > > > > > >
> > > > > > > diff --git a/drivers/firmware/efi/libstub/riscv-stub.c
> > > > > > > b/drivers/firmware/efi/libstub/riscv-stub.c
> > > > > > > new file mode 100644
> > > > > > > index 000000000000..3935b29ea93a
> > > > > > > --- /dev/null
> > > > > > > +++ b/drivers/firmware/efi/libstub/riscv-stub.c
> > > > > > > @@ -0,0 +1,135 @@
> > > > > > > +// SPDX-License-Identifier: GPL-2.0
> > > > > > > +/*
> > > > > > > + * Copyright (C) 2013, 2014 Linaro Ltd; <roy.franz@xxxxxxxxxx
> > > > > > > >
> > > > > > > + * Copyright (C) 2020 Western Digital Corporation or its
> > > > > > > affiliates.
> > > > > > > + *
> > > > > > > + * This file implements the EFI boot stub for the RISC-V
> > > > > > > kernel.
> > > > > > > + * Adapted from ARM64 version at
> > > > > > > drivers/firmware/efi/libstub/arm64-stub.c.
> > > > > > > + */
> > > > > > > +
> > > > > > > +#include <linux/efi.h>
> > > > > > > +#include <linux/libfdt.h>
> > > > > > > +#include <linux/libfdt_env.h>
> > > > > > > +#include <asm/efi.h>
> > > > > > > +#include <asm/sections.h>
> > > > > > > +
> > > > > > > +#include "efistub.h"
> > > > > > > +/*
> > > > > > > + * RISCV requires the kernel image to placed TEXT_OFFSET bytes
> > > > > > > beyond a 2 MB
> > > > > > > + * aligned base for 64 bit and 4MB for 32 bit.
> > > > > > > + */
> > > > > > > +#if IS_ENABLED(CONFIG_64BIT)
> > > > > >
> > > > > > You can use #ifdef here
> > > > > >
> > > > >
> > > > > ok.
> > > > >
> > > > > > > +#define MIN_KIMG_ALIGN SZ_2M
> > > > > > > +#else
> > > > > > > +#define MIN_KIMG_ALIGN SZ_4M
> > > > > > > +#endif
> > > > > > > +/*
> > > > > > > + * TEXT_OFFSET ensures that we don't overwrite the firmware
> > > > > > > that
> > > > > > > probably sits
> > > > > > > + * at the beginning of the DRAM.
> > > > > > > + */
> > > > > >
> > > > > > Ugh. Really? On an EFI system, that memory should be reserved in
> > > > > > some
> > > > > > way, we shouldn't be able to stomp on it like that.
> > > > > >
> > > > >
> > > > > Currently, we reserve the initial 128KB for run time firmware(only
> > > > > openSBI for now, EDK2 later) by using PMP (physical memory
> > > > > protection).
> > > > > Any acess to that region from supervisor mode (i.e. U-Boot) will
> > > > > result
> > > > > in a fault.
> > > > >
> > > > > Is it mandatory for UEFI to reserve the beginning of the DRAM ?
> > > > >
> > > >
> > > > It is mandatory to describe which memory is usable and which memory
> > > > is
> > > > reserved. If this memory is not usable, you either describe it as
> > > > reserved, or not describe it at all. Describing it as usable memory,
> > > > allocating it for the kernel but with a hidden agreement that it is
> > > > reserved is highly likely to cause problems down the road.
> > > >
> > >
> > > I completely agree with you on this. We have been talking to have a
> > > booting guide and memory map document for RISC-V Linux to document all
> > > the idiosyncries of RISC-V. But that has not happend until now.
> > > Once, the ordered booting patches are merged, I will try to take a stab
> > > at it.
> > >
> > > Other than that, do we need to describe it somewhere in U-boot wrt to
> > > UEFI so that it doesn't allocate memory from that region ?
> > >
> >
> > It is an idiosyncrasy that the firmware should hide from the OS.
> >
> > What if GRUB comes along and attempts to allocate that memory? Do we
> > also have to teach it that the first 128 KB memory of free memory are
> > magic and should not be touched?
> >
> > So the answer is to mark it as reserved. This way, no UEFI tools,
> > bootloaders etc will ever try to use it.
>
> Sounds good to me. We are currently discussing the best approach to
> provide reserved memory
> information to U-Boot/EDK2. The idea is to U-Boot/EDK2 may have to
> update the DT with
> reserved-memory node so that Linux is aware of the reservation as well.

The discussion is happening on Github at:
https://github.com/riscv/riscv-sbi-doc/pull/37

Feel free to share your views in above mentioned Github link.

Regards,
Anup