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Date: Thu, 27 Feb 2020 19:53:08 +0000
From: Atish Patra <Atish.Patra@....com>
To: "ardb@...nel.org" <ardb@...nel.org>
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Subject: Re: [RFC PATCH 5/5] RISC-V: Add EFI stub support.
On Wed, 2020-02-26 at 08:28 +0100, Ard Biesheuvel wrote:
> On Wed, 26 Feb 2020 at 02:10, Atish Patra <atish.patra@....com>
> 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@....com>
> > ---
> > 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@...aro.org>
> > + * 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 ?
> > +#define TEXT_OFFSET MIN_KIMG_ALIGN
> > +
> > +typedef __attribute__((noreturn)) void
> > (*jump_kernel_func)(unsigned int,
> > + unsigned
> > long);
> > +
> > +efi_status_t check_platform_features(void)
> > +{
> > + return EFI_SUCCESS;
> > +}
> > +
> > +u64 get_boot_hartid_from_fdt(unsigned long fdt)
>
> static
>
> > +{
> > + int chosen_node, len;
> > + const fdt64_t *prop;
> > + uint64_t hartid = U64_MAX;
> > +
> > + chosen_node = fdt_path_offset((void *)fdt, "/chosen");
> > + if (chosen_node < 0)
> > + return hartid;
>
> Just return U64_MAX here
>
> > + prop = fdt_getprop((void *)fdt, chosen_node, "efi-boot-
> > hartid", &len);
>
> Please call this 'boot-hartid' not 'efi-boot-hartid' as the hartid
> value is independent of whether you boot via EFI or not.
>
> > + if (!prop || len != sizeof(u64))
> > + return hartid;
> > +
>
> Return U64_MAX
>
> > + hartid = fdt64_to_cpu(*prop);
> > +
>
> and just return the swabbed value, so you can get rid of the local
> var.
>
Fixed all the above issues. I changed it to u32 as u64 won't work on 32
bit systems.
> > + return hartid;
> > +}
> > +
> > +/*
> > + * Jump to real kernel here with following constraints.
> > + * 1. MMU should be disabled.
> > + * 2. a0 should contain hartid
> > + * 3. a1 should DT address
> > + */
> > +void __noreturn efi_enter_kernel(unsigned long entrypoint,
> > unsigned long fdt)
>
> This prototype has changed, and now includes the size of the fdt in
> param 3.
>
Ahh yes. Fixed.
> > +{
> > + unsigned long kernel_entry = entrypoint + _start_kernel -
> > _start;
>
> stext_offset ? It has a terrible name though, and I'll probably
> propose to change it at some point, for all arches. But you can still
> use it here.
>
Sure. I updated it with stext_offset.
> > + jump_kernel_func jump_kernel = (void (*)(unsigned int,
> > unsigned long))kernel_entry;
> > + u64 hartid = get_boot_hartid_from_fdt(fdt);
> > +
> > + if (hartid == U64_MAX)
> > + /* We can not use panic or BUG at this point */
> > + __asm__ __volatile__ ("ebreak");
> > + /* Disable MMU */
> > + csr_write(CSR_SATP, 0);
> > + jump_kernel(hartid, fdt);
> > +}
> > +
> > +efi_status_t handle_kernel_image(unsigned long *image_addr,
> > + unsigned long *image_size,
> > + unsigned long *reserve_addr,
> > + unsigned long *reserve_size,
> > + unsigned long dram_base,
> > + efi_loaded_image_t *image)
> > +{
> > + efi_status_t status;
> > + unsigned long kernel_size, kernel_memsize = 0;
> > + unsigned long preferred_offset;
> > +
> > + /*
> > + * The preferred offset of the kernel Image is TEXT_OFFSET
> > bytes beyond
> > + * a KIMG_ALIGN aligned base.
> > + */
> > + preferred_offset = round_up(dram_base, MIN_KIMG_ALIGN) +
> > TEXT_OFFSET;
> > +
> > + kernel_size = _edata - _start;
> > + kernel_memsize = kernel_size + (_end - _edata);
> > +
> > + /*
> > + * Try a straight allocation at the preferred offset.
> > + * This will work around the issue where, if dram_base ==
> > 0x0,
> > + * efi_low_alloc() refuses to allocate at 0x0 (to prevent
> > the
> > + * address of the allocation to be mistaken for a FAIL
> > return
> > + * value or a NULL pointer). It will also ensure that, on
> > + * platforms where the [dram_base, dram_base + TEXT_OFFSET)
> > + * interval is partially occupied by the firmware (like on
> > APM
> > + * Mustang), we can still place the kernel at the address
> > + * 'dram_base + TEXT_OFFSET'.
>
> Better drop this entire last sentence (unless it is relevant, but
> then
> rework it to drop the APM Mustang reference)
>
As stated above, RISC-V firmware occupies [dram_base, dram_base +
128K). That's why I thought this comment is useful. I should have
removed the mustand reference. I will update it.
> > + */
> > + if (*image_addr == preferred_offset)
> > + return EFI_SUCCESS;
> > +
> > + *image_addr = *reserve_addr = preferred_offset;
> > + *reserve_size = round_up(kernel_memsize, EFI_ALLOC_ALIGN);
> > +
> > + status = efi_bs_call(allocate_pages, EFI_ALLOCATE_ADDRESS,
> > + EFI_LOADER_DATA,
> > + *reserve_size / EFI_PAGE_SIZE,
> > + (efi_physical_addr_t
> > *)reserve_addr);
> > +
> > + if (status != EFI_SUCCESS) {
> > + *reserve_size = kernel_memsize + TEXT_OFFSET;
> > + status = efi_low_alloc(*reserve_size,
> > MIN_KIMG_ALIGN,
> > + reserve_addr);
> > +
> > + if (status != EFI_SUCCESS) {
> > + pr_efi_err("Failed to relocate kernel\n");
> > + *reserve_size = 0;
> > + return status;
> > + }
> > + *image_addr = *reserve_addr + TEXT_OFFSET;
> > + }
> > + memcpy((void *)*image_addr, image->image_base,
> > kernel_size);
> > +
> > + return EFI_SUCCESS;
> > +}
> > --
> > 2.24.0
> >
--
Regards,
Atish
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