Commit 6bd33e1e authored by Christoph Hellwig's avatar Christoph Hellwig Committed by Paul Walmsley
Browse files

riscv: add nommu support 



The kernel runs in M-mode without using page tables, and thus can't run
bare metal without help from additional firmware.

Most of the patch is just stubbing out code not needed without page
tables, but there is an interesting detail in the signals implementation:

 - The normal RISC-V syscall ABI only implements rt_sigreturn as VDSO
   entry point, but the ELF VDSO is not supported for nommu Linux.
   We instead copy the code to call the syscall onto the stack.

In addition to enabling the nommu code a new defconfig for a small
kernel image that can run in nommu mode on qemu is also provided, to run
a kernel in qemu you can use the following command line:

qemu-system-riscv64 -smp 2 -m 64 -machine virt -nographic \
	-kernel arch/riscv/boot/loader \
	-drive file=rootfs.ext2,format=raw,id=hd0 \
	-device virtio-blk-device,drive=hd0

Contains contributions from Damien Le Moal <Damien.LeMoal@wdc.com>.

Signed-off-by: default avatarChristoph Hellwig <hch@lst.de>
Reviewed-by: default avatarAnup Patel <anup@brainfault.org>
[paul.walmsley@sifive.com: updated to apply; add CONFIG_MMU guards
 around PCI_IOBASE definition to fix build issues; fixed checkpatch
 issues; move the PCI_IO_* and VMEMMAP address space macros along
 with the others; resolve sparse warning]
Signed-off-by: default avatarPaul Walmsley <paul.walmsley@sifive.com>
parent 9e806356

arch/riscv/Kconfig

+17 −9
Original line number Diff line number Diff line
@@ -26,14 +26,14 @@ config RISCV 
	select GENERIC_IRQ_SHOW

	select GENERIC_PCI_IOMAP

	select GENERIC_SCHED_CLOCK

	select GENERIC_STRNCPY_FROM_USER

	select GENERIC_STRNLEN_USER

	select GENERIC_STRNCPY_FROM_USER if MMU

	select GENERIC_STRNLEN_USER if MMU

	select GENERIC_SMP_IDLE_THREAD

	select GENERIC_ATOMIC64 if !64BIT

	select HAVE_ARCH_AUDITSYSCALL

	select HAVE_ASM_MODVERSIONS

	select HAVE_MEMBLOCK_NODE_MAP

	select HAVE_DMA_CONTIGUOUS

	select HAVE_DMA_CONTIGUOUS if MMU

	select HAVE_FUTEX_CMPXCHG if FUTEX

	select HAVE_PERF_EVENTS

	select HAVE_PERF_REGS
@@ -50,6 +50,7 @@ config RISCV 
	select PCI_DOMAINS_GENERIC if PCI

	select PCI_MSI if PCI

	select RISCV_TIMER

	select UACCESS_MEMCPY if !MMU

	select GENERIC_IRQ_MULTI_HANDLER

	select GENERIC_ARCH_TOPOLOGY if SMP

	select ARCH_HAS_PTE_SPECIAL
@@ -60,7 +61,7 @@ config RISCV 
	select ARCH_WANT_HUGE_PMD_SHARE if 64BIT

	select SPARSEMEM_STATIC if 32BIT

	select ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT if MMU

	select HAVE_ARCH_MMAP_RND_BITS

	select HAVE_ARCH_MMAP_RND_BITS if MMU



config ARCH_MMAP_RND_BITS_MIN

	default 18 if 64BIT
@@ -75,6 +76,7 @@ config ARCH_MMAP_RND_BITS_MAX 
# set if we run in machine mode, cleared if we run in supervisor mode

config RISCV_M_MODE

	bool

	default !MMU



# set if we are running in S-mode and can use SBI calls

config RISCV_SBI
@@ -83,7 +85,11 @@ config RISCV_SBI 
	default y



config MMU

	def_bool y

	bool "MMU-based Paged Memory Management Support"

	default y

	help

	  Select if you want MMU-based virtualised addressing space

	  support by paged memory management. If unsure, say 'Y'.



config ZONE_DMA32

	bool
@@ -102,6 +108,7 @@ config PA_BITS 
config PAGE_OFFSET

	hex

	default 0xC0000000 if 32BIT && MAXPHYSMEM_2GB

	default 0x80000000 if 64BIT && !MMU

	default 0xffffffff80000000 if 64BIT && MAXPHYSMEM_2GB

	default 0xffffffe000000000 if 64BIT && MAXPHYSMEM_128GB
@@ -145,7 +152,7 @@ config GENERIC_HWEIGHT 
	def_bool y



config FIX_EARLYCON_MEM

	def_bool y

	def_bool CONFIG_MMU



config PGTABLE_LEVELS

	int
@@ -170,6 +177,7 @@ config ARCH_RV32I 
	select GENERIC_LIB_ASHRDI3

	select GENERIC_LIB_LSHRDI3

	select GENERIC_LIB_UCMPDI2

	select MMU



config ARCH_RV64I

	bool "RV64I"
@@ -178,9 +186,9 @@ config ARCH_RV64I 
	select HAVE_FUNCTION_TRACER

	select HAVE_FUNCTION_GRAPH_TRACER

	select HAVE_FTRACE_MCOUNT_RECORD

	select HAVE_DYNAMIC_FTRACE

	select HAVE_DYNAMIC_FTRACE_WITH_REGS

	select SWIOTLB

	select HAVE_DYNAMIC_FTRACE if MMU

	select HAVE_DYNAMIC_FTRACE_WITH_REGS if HAVE_DYNAMIC_FTRACE

	select SWIOTLB if MMU



endchoice

arch/riscv/configs/nommu_virt_defconfig

0 → 100644
+78 −0
Original line number Diff line number Diff line 
# CONFIG_CPU_ISOLATION is not set

CONFIG_LOG_BUF_SHIFT=16

CONFIG_PRINTK_SAFE_LOG_BUF_SHIFT=12

CONFIG_BLK_DEV_INITRD=y

# CONFIG_RD_BZIP2 is not set

# CONFIG_RD_LZMA is not set

# CONFIG_RD_XZ is not set

# CONFIG_RD_LZO is not set

# CONFIG_RD_LZ4 is not set

CONFIG_CC_OPTIMIZE_FOR_SIZE=y

CONFIG_EXPERT=y

# CONFIG_SYSFS_SYSCALL is not set

# CONFIG_FHANDLE is not set

# CONFIG_BASE_FULL is not set

# CONFIG_EPOLL is not set

# CONFIG_SIGNALFD is not set

# CONFIG_TIMERFD is not set

# CONFIG_EVENTFD is not set

# CONFIG_AIO is not set

# CONFIG_IO_URING is not set

# CONFIG_ADVISE_SYSCALLS is not set

# CONFIG_MEMBARRIER is not set

# CONFIG_KALLSYMS is not set

# CONFIG_VM_EVENT_COUNTERS is not set

# CONFIG_COMPAT_BRK is not set

CONFIG_SLOB=y

# CONFIG_SLAB_MERGE_DEFAULT is not set

# CONFIG_MMU is not set

CONFIG_MAXPHYSMEM_2GB=y

CONFIG_SMP=y

CONFIG_CMDLINE="root=/dev/vda rw earlycon=uart8250,mmio,0x10000000,115200n8 console=ttyS0"

CONFIG_CMDLINE_FORCE=y

# CONFIG_BLK_DEV_BSG is not set

CONFIG_PARTITION_ADVANCED=y

# CONFIG_MSDOS_PARTITION is not set

# CONFIG_EFI_PARTITION is not set

# CONFIG_MQ_IOSCHED_DEADLINE is not set

# CONFIG_MQ_IOSCHED_KYBER is not set

CONFIG_BINFMT_FLAT=y

# CONFIG_COREDUMP is not set

CONFIG_DEVTMPFS=y

CONFIG_DEVTMPFS_MOUNT=y

# CONFIG_FW_LOADER is not set

# CONFIG_ALLOW_DEV_COREDUMP is not set

CONFIG_VIRTIO_BLK=y

# CONFIG_INPUT_KEYBOARD is not set

# CONFIG_INPUT_MOUSE is not set

# CONFIG_SERIO is not set

# CONFIG_LEGACY_PTYS is not set

# CONFIG_LDISC_AUTOLOAD is not set

# CONFIG_DEVMEM is not set

CONFIG_SERIAL_8250=y

# CONFIG_SERIAL_8250_DEPRECATED_OPTIONS is not set

CONFIG_SERIAL_8250_CONSOLE=y

CONFIG_SERIAL_8250_NR_UARTS=1

CONFIG_SERIAL_8250_RUNTIME_UARTS=1

CONFIG_SERIAL_OF_PLATFORM=y

# CONFIG_HW_RANDOM is not set

# CONFIG_HWMON is not set

# CONFIG_LCD_CLASS_DEVICE is not set

# CONFIG_BACKLIGHT_CLASS_DEVICE is not set

# CONFIG_VGA_CONSOLE is not set

# CONFIG_HID is not set

# CONFIG_USB_SUPPORT is not set

CONFIG_VIRTIO_MMIO=y

CONFIG_VIRTIO_MMIO_CMDLINE_DEVICES=y

CONFIG_SIFIVE_PLIC=y

# CONFIG_VALIDATE_FS_PARSER is not set

CONFIG_EXT2_FS=y

# CONFIG_DNOTIFY is not set

# CONFIG_INOTIFY_USER is not set

# CONFIG_MISC_FILESYSTEMS is not set

CONFIG_LSM="[]"

CONFIG_PRINTK_TIME=y

# CONFIG_SCHED_DEBUG is not set

# CONFIG_RCU_TRACE is not set

# CONFIG_FTRACE is not set

# CONFIG_RUNTIME_TESTING_MENU is not set

arch/riscv/include/asm/cache.h

+8 −0
Original line number Diff line number Diff line
@@ -11,4 +11,12 @@ 


#define L1_CACHE_BYTES		(1 << L1_CACHE_SHIFT)



/*

 * RISC-V requires the stack pointer to be 16-byte aligned, so ensure that

 * the flat loader aligns it accordingly.

 */

#ifndef CONFIG_MMU

#define ARCH_SLAB_MINALIGN	16

#endif



#endif /* _ASM_RISCV_CACHE_H */

arch/riscv/include/asm/elf.h

+2 −2
Original line number Diff line number Diff line
@@ -56,16 +56,16 @@ extern unsigned long elf_hwcap; 
 */

#define ELF_PLATFORM	(NULL)



#ifdef CONFIG_MMU

#define ARCH_DLINFO						\

do {								\

	NEW_AUX_ENT(AT_SYSINFO_EHDR,				\

		(elf_addr_t)current->mm->context.vdso);		\

} while (0)





#define ARCH_HAS_SETUP_ADDITIONAL_PAGES

struct linux_binprm;

extern int arch_setup_additional_pages(struct linux_binprm *bprm,

	int uses_interp);

#endif /* CONFIG_MMU */



#endif /* _ASM_RISCV_ELF_H */

arch/riscv/include/asm/fixmap.h

+2 −0
Original line number Diff line number Diff line
@@ -11,6 +11,7 @@ 
#include <asm/page.h>

#include <asm/pgtable.h>



#ifdef CONFIG_MMU

/*

 * Here we define all the compile-time 'special' virtual addresses.

 * The point is to have a constant address at compile time, but to
@@ -42,4 +43,5 @@ extern void __set_fixmap(enum fixed_addresses idx, 


#include <asm-generic/fixmap.h>



#endif /* CONFIG_MMU */

#endif /* _ASM_RISCV_FIXMAP_H */

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