[v5,1/1] riscv: Allow to downgrade paging mode from the command line
Commit Message
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 | 34 ++++++++++++
arch/riscv/kernel/pi/cmdline_early.c | 55 +++++++++++++++++++
arch/riscv/lib/memcpy.S | 2 +
arch/riscv/lib/memmove.S | 2 +
arch/riscv/mm/init.c | 36 ++++++++++--
7 files changed, 129 insertions(+), 7 deletions(-)
create mode 100644 arch/riscv/kernel/pi/Makefile
create mode 100644 arch/riscv/kernel/pi/cmdline_early.c
Comments
Hi Alexandre,
Thank you for the patch! Perhaps something to improve:
[auto build test WARNING on linus/master]
[also build test WARNING on v6.2]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]
url: https://github.com/intel-lab-lkp/linux/commits/Alexandre-Ghiti/riscv-Allow-to-downgrade-paging-mode-from-the-command-line/20230222-184549
patch link: https://lore.kernel.org/r/20230222104322.1197763-2-alexghiti%40rivosinc.com
patch subject: [PATCH v5 1/1] riscv: Allow to downgrade paging mode from the command line
config: riscv-randconfig-r042-20230222 (https://download.01.org/0day-ci/archive/20230222/202302222359.LdNxjl1c-lkp@intel.com/config)
compiler: clang version 17.0.0 (https://github.com/llvm/llvm-project db89896bbbd2251fff457699635acbbedeead27f)
reproduce (this is a W=1 build):
wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
chmod +x ~/bin/make.cross
# install riscv cross compiling tool for clang build
# apt-get install binutils-riscv64-linux-gnu
# https://github.com/intel-lab-lkp/linux/commit/f92dd2e351d9f51f678f2d7ac63cc3cf85effddd
git remote add linux-review https://github.com/intel-lab-lkp/linux
git fetch --no-tags linux-review Alexandre-Ghiti/riscv-Allow-to-downgrade-paging-mode-from-the-command-line/20230222-184549
git checkout f92dd2e351d9f51f678f2d7ac63cc3cf85effddd
# save the config file
mkdir build_dir && cp config build_dir/.config
COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross W=1 O=build_dir ARCH=riscv olddefconfig
COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross W=1 O=build_dir ARCH=riscv SHELL=/bin/bash arch/riscv/kernel/pi/
If you fix the issue, kindly add following tag where applicable
| Reported-by: kernel test robot <lkp@intel.com>
| Link: https://lore.kernel.org/oe-kbuild-all/202302222359.LdNxjl1c-lkp@intel.com/
All warnings (new ones prefixed by >>):
>> arch/riscv/kernel/pi/cmdline_early.c:50:12: warning: no previous prototype for function 'set_satp_mode_from_cmdline' [-Wmissing-prototypes]
u64 __init set_satp_mode_from_cmdline(uintptr_t dtb_pa)
^
arch/riscv/kernel/pi/cmdline_early.c:50:1: note: declare 'static' if the function is not intended to be used outside of this translation unit
u64 __init set_satp_mode_from_cmdline(uintptr_t dtb_pa)
^
static
1 warning generated.
vim +/set_satp_mode_from_cmdline +50 arch/riscv/kernel/pi/cmdline_early.c
49
> 50 u64 __init set_satp_mode_from_cmdline(uintptr_t dtb_pa)
@@ -3578,7 +3578,10 @@
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.
@@ -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-y += pi/
new file mode 100644
@@ -0,0 +1,34 @@
+# 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 \
+ $(call cc-option,-fno-addrsig)
+
+GCOV_PROFILE := n
+KASAN_SANITIZE := n
+KCSAN_SANITIZE := n
+UBSAN_SANITIZE := n
+KCOV_INSTRUMENT := n
+
+$(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))
new file mode 100644
@@ -0,0 +1,55 @@
+// 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] __initdata;
+
+static char * __init 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 __init match_noXlvl(char *cmdline)
+{
+ if (strstr(cmdline, "no4lvl"))
+ return SATP_MODE_48;
+ else if (strstr(cmdline, "no5lvl"))
+ return SATP_MODE_57;
+
+ return 0;
+}
+
+u64 __init set_satp_mode_from_cmdline(uintptr_t dtb_pa)
+{
+ char *cmdline = get_early_cmdline(dtb_pa);
+
+ return match_noXlvl(cmdline);
+}
@@ -106,3 +106,5 @@ WEAK(memcpy)
6:
ret
END(__memcpy)
+SYM_FUNC_ALIAS(__pi_memcpy, __memcpy)
+SYM_FUNC_ALIAS(__pi___memcpy, __memcpy)
@@ -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)
@@ -732,6 +732,8 @@ 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;
@@ -746,17 +748,39 @@ 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,
@@ -775,7 +799,8 @@ 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;
@@ -786,9 +811,8 @@ 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;
}
@@ -979,7 +1003,7 @@ 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
kernel_map.va_pa_offset = PAGE_OFFSET - kernel_map.phys_addr;