Date:   Wed, 22 Apr 2020 17:45:18 +0000
From:   Atish Patra <Atish.Patra@....com>
To:     "palmer@...belt.com" <palmer@...belt.com>
CC:     "linux-efi@...r.kernel.org" <linux-efi@...r.kernel.org>,
        "linux-riscv@...ts.infradead.org" <linux-riscv@...ts.infradead.org>,
        "xypron.glpk@....de" <xypron.glpk@....de>,
        "masahiroy@...nel.org" <masahiroy@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "ardb@...nel.org" <ardb@...nel.org>
Subject: Re: [v4 PATCH 3/3] RISC-V: Add EFI stub support.

On Tue, 2020-04-21 at 13:08 -0700, Palmer Dabbelt wrote:
> On Mon, 20 Apr 2020 20:33:36 PDT (-0700), Atish Patra 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 +
> >  arch/riscv/include/asm/efi.h              |  44 +++++++++
> >  drivers/firmware/efi/Kconfig              |   2 +-
> >  drivers/firmware/efi/libstub/Makefile     |  10 ++
> >  drivers/firmware/efi/libstub/riscv-stub.c | 106
> > ++++++++++++++++++++++
> >  7 files changed, 183 insertions(+), 1 deletion(-)
> >  create mode 100644 arch/riscv/include/asm/efi.h
> >  create mode 100644 drivers/firmware/efi/libstub/riscv-stub.c
> > 
> > diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> > index f39e326a7a42..eb4f41c8f3ce 100644
> > --- a/arch/riscv/Kconfig
> > +++ b/arch/riscv/Kconfig
> > @@ -379,10 +379,30 @@ 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_STUB
> 
> So I guess just "select RISCV_ISA_C" would be sufficient to make this
> work, but
> I still feel flike an explicit "c.li" is saner.
> 

will fix it.

> > +	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 fb6e37db836d..079435804d6d 100644
> > --- a/arch/riscv/Makefile
> > +++ b/arch/riscv/Makefile
> > @@ -80,6 +80,7 @@ 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 4da4886246a4..ae69e12d306a 100644
> > --- a/arch/riscv/configs/defconfig
> > +++ b/arch/riscv/configs/defconfig
> > @@ -129,3 +129,4 @@ CONFIG_DEBUG_BLOCK_EXT_DEVT=y
> >  # CONFIG_RUNTIME_TESTING_MENU is not set
> >  CONFIG_MEMTEST=y
> >  # CONFIG_SYSFS_SYSCALL is not set
> > +CONFIG_EFI=y
> > diff --git a/arch/riscv/include/asm/efi.h
> > b/arch/riscv/include/asm/efi.h
> > new file mode 100644
> > index 000000000000..62d7d5eafed8
> > --- /dev/null
> > +++ b/arch/riscv/include/asm/efi.h
> > @@ -0,0 +1,44 @@
> > +/* SPDX-License-Identifier: GPL-2.0 */
> > +/*
> > + * Copyright (C) 2020 Western Digital Corporation or its
> > affiliates.
> > + * Based on arch/arm64/include/asm/efi.h
> > + */
> > +#ifndef _ASM_EFI_H
> > +#define _ASM_EFI_H
> > +
> > +#include <asm/io.h>
> > +#include <asm/mmu_context.h>
> > +#include <asm/ptrace.h>
> > +#include <asm/tlbflush.h>
> > +
> > +#define VA_BITS_MIN 39
> 
> I don't see this actually being used, but if it's releant to some
> macro that
> I'm missing then EFI support should depend on rv64.
> 

Yeah. This was a left over from the previous patch. Thanks for pointing
out. I will remove it.

> > +
> > +/* on RISC-V, the FDT may be located anywhere in system RAM */
> > +static inline unsigned long efi_get_max_fdt_addr(unsigned long
> > dram_base)
> > +{
> > +	return ULONG_MAX;
> > +}
> > +
> > +/* Load initrd at enough distance from DRAM start */
> > +static inline unsigned long efi_get_max_initrd_addr(unsigned long
> > dram_base,
> > +						    unsigned long
> > image_addr)
> > +{
> > +	return dram_base + SZ_256M;
> > +}
> > +
> > +#define efi_bs_call(func, ...)	efi_system_table()->boottime-
> > >func(__VA_ARGS__)
> > +#define efi_rt_call(func, ...)	efi_system_table()->runtime-
> > >func(__VA_ARGS__)
> > +#define efi_is_native()		(true)
> > +
> > +#define efi_table_attr(inst, attr)	(inst->attr)
> > +
> > +#define efi_call_proto(inst, func, ...) inst->func(inst,
> > ##__VA_ARGS__)
> > +
> > +#define alloc_screen_info(x...)		(&screen_info)
> > +extern char stext_offset[];
> > +
> > +static inline void free_screen_info(struct screen_info *si)
> > +{
> > +}
> > +
> > +#endif /* _ASM_EFI_H */
> > diff --git a/drivers/firmware/efi/Kconfig
> > b/drivers/firmware/efi/Kconfig
> > index 2a2b2b96a1dc..fcdc789d3f87 100644
> > --- a/drivers/firmware/efi/Kconfig
> > +++ b/drivers/firmware/efi/Kconfig
> > @@ -111,7 +111,7 @@ config EFI_GENERIC_STUB
> > 
> >  config EFI_ARMSTUB_DTB_LOADER
> >  	bool "Enable the DTB loader"
> > -	depends on EFI_GENERIC_STUB
> > +	depends on EFI_GENERIC_STUB && !RISCV
> >  	default y
> >  	help
> >  	  Select this config option to add support for the dtb= command
> > diff --git a/drivers/firmware/efi/libstub/Makefile
> > b/drivers/firmware/efi/libstub/Makefile
> > index 0f57293d777e..eb365c55c0fe 100644
> > --- a/drivers/firmware/efi/libstub/Makefile
> > +++ b/drivers/firmware/efi/libstub/Makefile
> > @@ -22,6 +22,8 @@ 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-$(CONFIG_EFI_GENERIC_STUB) +=
> > -I$(srctree)/scripts/dtc/libfdt
> > 
> > @@ -57,6 +59,7 @@ lib-$(CONFIG_EFI_GENERIC_STUB)	+= efi-stub.o
> > fdt.o string.o \
> >  lib-$(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=$(TEXT_OFFSET)
> > 
> > @@ -100,6 +103,13 @@ STUBCOPY_FLAGS-$(CONFIG_X86)	+= --rename-
> > section .bss=.bss.efistub,load,alloc
> >  STUBCOPY_RELOC-$(CONFIG_X86_32)	:= R_386_32
> >  STUBCOPY_RELOC-$(CONFIG_X86_64)	:= R_X86_64_64
> > 
> > +# For RISC-V, we don't need anything special other than arm64.
> > Keep all the
> > +# symbols in .init section and make sure that no absolute symbols
> > references
> > +# doesn't exist.
> > +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..bd1d6fed8754
> > --- /dev/null
> > +++ b/drivers/firmware/efi/libstub/riscv-stub.c
> > @@ -0,0 +1,106 @@
> > +// 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"
> > +/*
> > + * RISC-V requires the kernel image to placed 2 MB aligned base
> > for 64 bit and
> > + * 4MB for 32 bit.
> > + */
> > +#ifdef CONFIG_64BIT
> > +#define MIN_KIMG_ALIGN	SZ_2M
> > +#else
> > +#define MIN_KIMG_ALIGN	SZ_4M
> > +#endif
> > +
> > +typedef __attribute__((noreturn)) void
> > (*jump_kernel_func)(unsigned int,
> > +							   unsigned
> > long);
> > +efi_status_t check_platform_features(void)
> > +{
> > +	return EFI_SUCCESS;
> > +}
> > +
> > +static u32 get_boot_hartid_from_fdt(unsigned long fdt)
> > +{
> > +	int chosen_node, len;
> > +	const fdt32_t *prop;
> > +
> > +	chosen_node = fdt_path_offset((void *)fdt, "/chosen");
> > +	if (chosen_node < 0)
> > +		return U32_MAX;
> > +	prop = fdt_getprop((void *)fdt, chosen_node, "boot-hartid",
> > &len);
> > +	if (!prop || len != sizeof(u32))
> > +		return U32_MAX;
> > +
> > +	return fdt32_to_cpu(*prop);
> > +}
> > +
> > +/*
> > + * 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,
> > +				 unsigned long fdt_size)
> > +{
> > +	unsigned long kernel_entry = entrypoint + (unsigned
> > long)stext_offset;
> > +	jump_kernel_func jump_kernel = (jump_kernel_func) kernel_entry;
> > +	u32 hartid = get_boot_hartid_from_fdt(fdt);
> > +
> > +	if (hartid == U32_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 = 0;
> > +	unsigned long preferred_addr;
> > +
> > +	kernel_size = _edata - _start;
> > +	*reserve_size = kernel_size + (_end - _edata);
> > +	*image_addr = (unsigned long)_start;
> > +
> > +	/*
> > +	 * RISC-V kernel maps PAGE_OFFSET virtual address to the same
> > physical
> > +	 * address where kernel is booted. That's why kernel should
> > boot from
> > +	 * as low as possible to avoid wastage of memory. Currently,
> > dram_base
> > +	 * is occupied by the firmware. So the preferred address for
> > kernel to
> > +	 * boot is next aligned address. If preferred address is not
> > available,
> > +	 * relocate_kernel will fall back to efi_low_alloc_above to
> > allocate
> > +	 * lowest possible memory region as long as the address and
> > size meets
> > +	 * the alignment constraints.
> > +	 */
> > +	preferred_addr = round_up(dram_base, MIN_KIMG_ALIGN) +
> > MIN_KIMG_ALIGN;
> > +	status = efi_relocate_kernel(image_addr, kernel_size,
> > *reserve_size,
> > +				     preferred_addr, MIN_KIMG_ALIGN,
> > dram_base);
> > +
> > +	if (status != EFI_SUCCESS) {
> > +		pr_efi_err("Failed to relocate kernel\n");
> > +		*reserve_size = 0;
> > +		return status;
> > +	}
> > +
> > +	return EFI_SUCCESS;
> > +}

-- 
Regards,
Atish

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