Messages in this thread Patch in this message | | | Date | Thu, 20 Apr 2023 10:36:43 -0700 (PDT) | Subject | Re: [PATCH v9 1/1] riscv: Allow to downgrade paging mode from the command line | From | Palmer Dabbelt <> |
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On Tue, 28 Mar 2023 22:09:51 PDT (-0700), alexghiti@rivosinc.com wrote: > Add 2 early command line parameters that allow to downgrade satp mode > (using the same naming as x86): > - "no5lvl": use a 4-level page table (down from sv57 to sv48) > - "no4lvl": use a 3-level page table (down from sv57/sv48 to sv39) > > Note that going through the device tree to get the kernel command line > works with ACPI too since the efi stub creates a device tree anyway with > the command line. > > In KASAN kernels, we can't use the libfdt that early in the boot process > since we are not ready to execute instrumented functions. So instead of > using the "generic" libfdt, we compile our own versions of those functions > that are not instrumented and that are prefixed so that they do not > conflict with the generic ones. We also need the non-instrumented versions > of the string functions and the prefixed versions of memcpy/memmove. > > This is largely inspired by commit aacd149b6238 ("arm64: head: avoid > relocating the kernel twice for KASLR") from which I removed compilation > flags that were not relevant to RISC-V at the moment (LTO, SCS, pie). > > Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com> > Tested-by: Björn Töpel <bjorn@rivosinc.com> > Reviewed-by: Björn Töpel <bjorn@rivosinc.com> > --- > .../admin-guide/kernel-parameters.txt | 5 +- > arch/riscv/kernel/Makefile | 2 + > arch/riscv/kernel/pi/Makefile | 39 ++++++++++++ > arch/riscv/kernel/pi/cmdline_early.c | 62 +++++++++++++++++++ > arch/riscv/kernel/vmlinux.lds.S | 8 +++ > arch/riscv/lib/memcpy.S | 2 + > arch/riscv/lib/memmove.S | 2 + > arch/riscv/lib/strlen.S | 1 + > arch/riscv/mm/init.c | 36 +++++++++-- > 9 files changed, 150 insertions(+), 7 deletions(-) > create mode 100644 arch/riscv/kernel/pi/Makefile > create mode 100644 arch/riscv/kernel/pi/cmdline_early.c > > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt > index 6221a1d057dd..accc400b43f1 100644 > --- a/Documentation/admin-guide/kernel-parameters.txt > +++ b/Documentation/admin-guide/kernel-parameters.txt > @@ -3576,7 +3576,10 @@ > emulation library even if a 387 maths coprocessor > is present. > > - no5lvl [X86-64] Disable 5-level paging mode. Forces > + no4lvl [RISCV] Disable 4-level and 5-level paging modes. Forces > + kernel to use 3-level paging instead. > + > + no5lvl [X86-64,RISCV] Disable 5-level paging mode. Forces > kernel to use 4-level paging instead. > > nofsgsbase [X86] Disables FSGSBASE instructions. > diff --git a/arch/riscv/kernel/Makefile b/arch/riscv/kernel/Makefile > index 4cf303a779ab..aa22f87faeae 100644 > --- a/arch/riscv/kernel/Makefile > +++ b/arch/riscv/kernel/Makefile > @@ -89,3 +89,5 @@ obj-$(CONFIG_EFI) += efi.o > obj-$(CONFIG_COMPAT) += compat_syscall_table.o > obj-$(CONFIG_COMPAT) += compat_signal.o > obj-$(CONFIG_COMPAT) += compat_vdso/ > + > +obj-$(CONFIG_64BIT) += pi/ > diff --git a/arch/riscv/kernel/pi/Makefile b/arch/riscv/kernel/pi/Makefile > new file mode 100644 > index 000000000000..42c58f4ab53b > --- /dev/null > +++ b/arch/riscv/kernel/pi/Makefile > @@ -0,0 +1,39 @@ > +# SPDX-License-Identifier: GPL-2.0 > +# This file was copied from arm64/kernel/pi/Makefile. > + > +KBUILD_CFLAGS := $(subst $(CC_FLAGS_FTRACE),,$(KBUILD_CFLAGS)) \ > + -Os -DDISABLE_BRANCH_PROFILING $(DISABLE_STACKLEAK_PLUGIN) \ > + $(call cc-option,-mbranch-protection=none) \ > + -I$(srctree)/scripts/dtc/libfdt -fno-stack-protector \ > + -D__DISABLE_EXPORTS -ffreestanding \ > + -fno-asynchronous-unwind-tables -fno-unwind-tables \ > + $(call cc-option,-fno-addrsig) > + > +KBUILD_CFLAGS += -mcmodel=medany > + > +CFLAGS_cmdline_early.o += -D__NO_FORTIFY > +CFLAGS_lib-fdt_ro.o += -D__NO_FORTIFY > + > +GCOV_PROFILE := n > +KASAN_SANITIZE := n > +KCSAN_SANITIZE := n > +UBSAN_SANITIZE := n > +KCOV_INSTRUMENT := n > + > +$(obj)/%.pi.o: OBJCOPYFLAGS := --prefix-symbols=__pi_ \ > + --remove-section=.note.gnu.property \ > + --prefix-alloc-sections=.init > +$(obj)/%.pi.o: $(obj)/%.o FORCE > + $(call if_changed,objcopy) > + > +$(obj)/lib-%.o: $(srctree)/lib/%.c FORCE > + $(call if_changed_rule,cc_o_c) > + > +$(obj)/string.o: $(srctree)/lib/string.c FORCE > + $(call if_changed_rule,cc_o_c) > + > +$(obj)/ctype.o: $(srctree)/lib/ctype.c FORCE > + $(call if_changed_rule,cc_o_c) > + > +obj-y := cmdline_early.pi.o string.pi.o ctype.pi.o lib-fdt.pi.o lib-fdt_ro.pi.o > +extra-y := $(patsubst %.pi.o,%.o,$(obj-y)) > diff --git a/arch/riscv/kernel/pi/cmdline_early.c b/arch/riscv/kernel/pi/cmdline_early.c > new file mode 100644 > index 000000000000..05652d13c746 > --- /dev/null > +++ b/arch/riscv/kernel/pi/cmdline_early.c > @@ -0,0 +1,62 @@ > +// SPDX-License-Identifier: GPL-2.0-only > +#include <linux/types.h> > +#include <linux/init.h> > +#include <linux/libfdt.h> > +#include <linux/string.h> > +#include <asm/pgtable.h> > +#include <asm/setup.h> > + > +static char early_cmdline[COMMAND_LINE_SIZE]; > + > +/* > + * Declare the functions that are exported (but prefixed) here so that LLVM > + * does not complain it lacks the 'static' keyword (which, if added, makes > + * LLVM complain because the function is actually unused in this file). > + */ > +u64 set_satp_mode_from_cmdline(uintptr_t dtb_pa); > + > +static char *get_early_cmdline(uintptr_t dtb_pa) > +{ > + const char *fdt_cmdline = NULL; > + unsigned int fdt_cmdline_size = 0; > + int chosen_node; > + > + if (!IS_ENABLED(CONFIG_CMDLINE_FORCE)) { > + chosen_node = fdt_path_offset((void *)dtb_pa, "/chosen"); > + if (chosen_node >= 0) { > + fdt_cmdline = fdt_getprop((void *)dtb_pa, chosen_node, > + "bootargs", NULL); > + if (fdt_cmdline) { > + fdt_cmdline_size = strlen(fdt_cmdline); > + strscpy(early_cmdline, fdt_cmdline, > + COMMAND_LINE_SIZE); > + } > + } > + } > + > + if (IS_ENABLED(CONFIG_CMDLINE_EXTEND) || > + IS_ENABLED(CONFIG_CMDLINE_FORCE) || > + fdt_cmdline_size == 0 /* CONFIG_CMDLINE_FALLBACK */) { > + strncat(early_cmdline, CONFIG_CMDLINE, > + COMMAND_LINE_SIZE - fdt_cmdline_size); > + } > + > + return early_cmdline; > +} > + > +static u64 match_noXlvl(char *cmdline) > +{ > + if (strstr(cmdline, "no4lvl")) > + return SATP_MODE_48; > + else if (strstr(cmdline, "no5lvl")) > + return SATP_MODE_57; > + > + return 0; > +} > + > +u64 set_satp_mode_from_cmdline(uintptr_t dtb_pa) > +{ > + char *cmdline = get_early_cmdline(dtb_pa); > + > + return match_noXlvl(cmdline); > +} > diff --git a/arch/riscv/kernel/vmlinux.lds.S b/arch/riscv/kernel/vmlinux.lds.S > index 615ff5842690..b12a843ad426 100644 > --- a/arch/riscv/kernel/vmlinux.lds.S > +++ b/arch/riscv/kernel/vmlinux.lds.S > @@ -83,6 +83,14 @@ SECTIONS > /* Start of init data section */ > __init_data_begin = .; > INIT_DATA_SECTION(16) > + > + /* Those sections result from the compilation of kernel/pi/string.c */ > + .init.pidata : { > + *(.init.srodata.cst8*) > + *(.init__bug_table*) > + *(.init.sdata*) > + } > + > .init.bss : { > *(.init.bss) /* from the EFI stub */ > } > diff --git a/arch/riscv/lib/memcpy.S b/arch/riscv/lib/memcpy.S > index 51ab716253fa..1a40d01a9543 100644 > --- a/arch/riscv/lib/memcpy.S > +++ b/arch/riscv/lib/memcpy.S > @@ -106,3 +106,5 @@ WEAK(memcpy) > 6: > ret > END(__memcpy) > +SYM_FUNC_ALIAS(__pi_memcpy, __memcpy) > +SYM_FUNC_ALIAS(__pi___memcpy, __memcpy) > diff --git a/arch/riscv/lib/memmove.S b/arch/riscv/lib/memmove.S > index e0609e1f0864..838ff2022fe3 100644 > --- a/arch/riscv/lib/memmove.S > +++ b/arch/riscv/lib/memmove.S > @@ -314,3 +314,5 @@ return_from_memmove: > > SYM_FUNC_END(memmove) > SYM_FUNC_END(__memmove) > +SYM_FUNC_ALIAS(__pi_memmove, __memmove) > +SYM_FUNC_ALIAS(__pi___memmove, __memmove) > diff --git a/arch/riscv/lib/strlen.S b/arch/riscv/lib/strlen.S > index 15bb8f3aa959..9d0055616f7b 100644 > --- a/arch/riscv/lib/strlen.S > +++ b/arch/riscv/lib/strlen.S > @@ -131,3 +131,4 @@ strlen_zbb: > .option pop > #endif > SYM_FUNC_END(strlen) > +SYM_FUNC_ALIAS(__pi_strlen, strlen) > diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c > index bce899b180cd..3ad771571c2d 100644 > --- a/arch/riscv/mm/init.c > +++ b/arch/riscv/mm/init.c > @@ -746,6 +746,8 @@ static __init pgprot_t pgprot_from_va(uintptr_t va) > #endif /* CONFIG_STRICT_KERNEL_RWX */ > > #if defined(CONFIG_64BIT) && !defined(CONFIG_XIP_KERNEL) > +u64 __pi_set_satp_mode_from_cmdline(uintptr_t dtb_pa); > + > static void __init disable_pgtable_l5(void) > { > pgtable_l5_enabled = false; > @@ -760,17 +762,39 @@ static void __init disable_pgtable_l4(void) > satp_mode = SATP_MODE_39; > } > > +static int __init print_no4lvl(char *p) > +{ > + pr_info("Disabled 4-level and 5-level paging"); > + return 0; > +} > +early_param("no4lvl", print_no4lvl); > + > +static int __init print_no5lvl(char *p) > +{ > + pr_info("Disabled 5-level paging"); > + return 0; > +} > +early_param("no5lvl", print_no5lvl); > + > /* > * There is a simple way to determine if 4-level is supported by the > * underlying hardware: establish 1:1 mapping in 4-level page table mode > * then read SATP to see if the configuration was taken into account > * meaning sv48 is supported. > */ > -static __init void set_satp_mode(void) > +static __init void set_satp_mode(uintptr_t dtb_pa) > { > u64 identity_satp, hw_satp; > uintptr_t set_satp_mode_pmd = ((unsigned long)set_satp_mode) & PMD_MASK; > - bool check_l4 = false; > + u64 satp_mode_cmdline = __pi_set_satp_mode_from_cmdline(dtb_pa); > + > + if (satp_mode_cmdline == SATP_MODE_57) { > + disable_pgtable_l5(); > + } else if (satp_mode_cmdline == SATP_MODE_48) { > + disable_pgtable_l5(); > + disable_pgtable_l4(); > + return; > + } > > create_p4d_mapping(early_p4d, > set_satp_mode_pmd, (uintptr_t)early_pud, > @@ -789,7 +813,8 @@ static __init void set_satp_mode(void) > retry: > create_pgd_mapping(early_pg_dir, > set_satp_mode_pmd, > - check_l4 ? (uintptr_t)early_pud : (uintptr_t)early_p4d, > + pgtable_l5_enabled ? > + (uintptr_t)early_p4d : (uintptr_t)early_pud, > PGDIR_SIZE, PAGE_TABLE); > > identity_satp = PFN_DOWN((uintptr_t)&early_pg_dir) | satp_mode; > @@ -800,9 +825,8 @@ static __init void set_satp_mode(void) > local_flush_tlb_all(); > > if (hw_satp != identity_satp) { > - if (!check_l4) { > + if (pgtable_l5_enabled) { > disable_pgtable_l5(); > - check_l4 = true; > memset(early_pg_dir, 0, PAGE_SIZE); > goto retry; > } > @@ -1031,7 +1055,7 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa) > #endif > > #if defined(CONFIG_64BIT) && !defined(CONFIG_XIP_KERNEL) > - set_satp_mode(); > + set_satp_mode(dtb_pa); > #endif > > /*
Alex found that we're missing -fpie, which was causing the LLVM boot failures. I'm just going to squash in
diff --git a/arch/riscv/kernel/pi/Makefile b/arch/riscv/kernel/pi/Makefile index 42c58f4ab53b..5d7cb991f2b8 100644 --- a/arch/riscv/kernel/pi/Makefile +++ b/arch/riscv/kernel/pi/Makefile @@ -1,7 +1,7 @@ # SPDX-License-Identifier: GPL-2.0 # This file was copied from arm64/kernel/pi/Makefile. -KBUILD_CFLAGS := $(subst $(CC_FLAGS_FTRACE),,$(KBUILD_CFLAGS)) \ +KBUILD_CFLAGS := $(subst $(CC_FLAGS_FTRACE),,$(KBUILD_CFLAGS)) -fpie \ -Os -DDISABLE_BRANCH_PROFILING $(DISABLE_STACKLEAK_PLUGIN) \ $(call cc-option,-mbranch-protection=none) \ -I$(srctree)/scripts/dtc/libfdt -fno-stack-protector \
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