On 11.06.19 00:16, Christoph Hellwig wrote:
> The kernel runs in M-mode without using page tables, and thus doesn't
> can run bare metal without help from additional firmware.
s/doesn't can/can't/
>
> 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.
Interesting read :)
>
> 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@xxxxxxx>.
>
> Signed-off-by: Christoph Hellwig <hch@xxxxxx>
> ---
> arch/riscv/Kconfig | 24 +++++---
> arch/riscv/configs/nommu_virt_defconfig | 78 +++++++++++++++++++++++++
> arch/riscv/include/asm/elf.h | 4 +-
> arch/riscv/include/asm/futex.h | 6 ++
> arch/riscv/include/asm/io.h | 4 ++
> arch/riscv/include/asm/mmu.h | 3 +
> arch/riscv/include/asm/page.h | 12 +++-
> arch/riscv/include/asm/pgalloc.h | 2 +
> arch/riscv/include/asm/pgtable.h | 38 ++++++++----
> arch/riscv/include/asm/tlbflush.h | 7 ++-
> arch/riscv/include/asm/uaccess.h | 4 ++
> arch/riscv/kernel/Makefile | 3 +-
> arch/riscv/kernel/entry.S | 11 ++++
> arch/riscv/kernel/head.S | 6 ++
> arch/riscv/kernel/signal.c | 17 +++++-
> arch/riscv/lib/Makefile | 8 +--
> arch/riscv/mm/Makefile | 3 +-
> arch/riscv/mm/cacheflush.c | 2 +
> arch/riscv/mm/context.c | 2 +
> arch/riscv/mm/init.c | 2 +
> 20 files changed, 200 insertions(+), 36 deletions(-)
> create mode 100644 arch/riscv/configs/nommu_virt_defconfig
>
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index 9f2ebd035e80..41edb314ec67 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -27,13 +27,13 @@ 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_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_SYSCALL_TRACEPOINTS
> @@ -48,6 +48,7 @@ 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 ARCH_HAS_PTE_SPECIAL
> select ARCH_HAS_MMIOWB
> @@ -56,9 +57,14 @@ config RISCV
> # set if we run in machine mode, cleared if we run in supervisor mode
> config M_MODE
> bool
> + default y if !MMU
>
> 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
> @@ -67,6 +73,7 @@ config ZONE_DMA32
> 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
>
> @@ -94,7 +101,7 @@ config GENERIC_HWEIGHT
> def_bool y
>
> config FIX_EARLYCON_MEM
> - def_bool y
> + def_bool CONFIG_MMU
>
> config PGTABLE_LEVELS
> int
> @@ -117,6 +124,7 @@ config ARCH_RV32I
> select GENERIC_LIB_ASHRDI3
> select GENERIC_LIB_LSHRDI3
> select GENERIC_LIB_UCMPDI2
> + select MMU
>
> config ARCH_RV64I
> bool "RV64I"
> @@ -125,9 +133,9 @@ 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
>
> diff --git a/arch/riscv/configs/nommu_virt_defconfig b/arch/riscv/configs/nommu_virt_defconfig
> new file mode 100644
> index 000000000000..cf74e179bf90
> --- /dev/null
> +++ b/arch/riscv/configs/nommu_virt_defconfig
> @@ -0,0 +1,78 @@
> +# 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
> diff --git a/arch/riscv/include/asm/elf.h b/arch/riscv/include/asm/elf.h
> index ef04084bf0de..d83a4efd052b 100644
> --- a/arch/riscv/include/asm/elf.h
> +++ b/arch/riscv/include/asm/elf.h
> @@ -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 */
> diff --git a/arch/riscv/include/asm/futex.h b/arch/riscv/include/asm/futex.h
> index 4ad6409c4647..418564b96dc4 100644
> --- a/arch/riscv/include/asm/futex.h
> +++ b/arch/riscv/include/asm/futex.h
> @@ -12,6 +12,12 @@
> #include <linux/errno.h>
> #include <asm/asm.h>
>
> +/* We don't even really need the extable code, but for now keep it simple */
> +#ifndef CONFIG_MMU
> +#define __enable_user_access() do { } while (0)
> +#define __disable_user_access() do { } while (0)
> +#endif
> +
> #define __futex_atomic_op(insn, ret, oldval, uaddr, oparg) \
> { \
> uintptr_t tmp; \
> diff --git a/arch/riscv/include/asm/io.h b/arch/riscv/include/asm/io.h
> index fc1189ad3777..d39a8f03e85e 100644
> --- a/arch/riscv/include/asm/io.h
> +++ b/arch/riscv/include/asm/io.h
> @@ -14,6 +14,7 @@
> #include <linux/types.h>
> #include <asm/mmiowb.h>
>
> +#ifdef CONFIG_MMU
> extern void __iomem *ioremap(phys_addr_t offset, unsigned long size);
>
> /*
> @@ -26,6 +27,9 @@ extern void __iomem *ioremap(phys_addr_t offset, unsigned long size);
> #define ioremap_wt(addr, size) ioremap((addr), (size))
>
> extern void iounmap(volatile void __iomem *addr);
> +#else
> +#define pgprot_noncached(x) (x)
> +#endif /* CONFIG_MMU */
>
> /* Generic IO read/write. These perform native-endian accesses. */
> #define __raw_writeb __raw_writeb
> diff --git a/arch/riscv/include/asm/mmu.h b/arch/riscv/include/asm/mmu.h
> index 151476fb58cb..967eacb01ab5 100644
> --- a/arch/riscv/include/asm/mmu.h
> +++ b/arch/riscv/include/asm/mmu.h
> @@ -10,6 +10,9 @@
> #ifndef __ASSEMBLY__
>
> typedef struct {
> +#ifndef CONFIG_MMU
> + unsigned long end_brk;
> +#endif
> void *vdso;
> #ifdef CONFIG_SMP
> /* A local icache flush is needed before user execution can resume. */
> diff --git a/arch/riscv/include/asm/page.h b/arch/riscv/include/asm/page.h
> index 8ddb6c7fedac..df0256a9a965 100644
> --- a/arch/riscv/include/asm/page.h
> +++ b/arch/riscv/include/asm/page.h
> @@ -78,8 +78,14 @@ typedef struct page *pgtable_t;
> #define PTE_FMT "%08lx"
> #endif
>
> +#ifdef CONFIG_MMU
> extern unsigned long va_pa_offset;
> extern unsigned long pfn_base;
> +#define ARCH_PFN_OFFSET (pfn_base)
> +#else
> +#define va_pa_offset 0
> +#define ARCH_PFN_OFFSET (PAGE_OFFSET >> PAGE_SHIFT)
> +#endif /* CONFIG_MMU */
>
> extern unsigned long max_low_pfn;
> extern unsigned long min_low_pfn;
> @@ -101,9 +107,7 @@ extern unsigned long min_low_pfn;
> #define phys_to_page(paddr) (pfn_to_page(phys_to_pfn(paddr)))
>
> #define pfn_valid(pfn) \
> - (((pfn) >= pfn_base) && (((pfn)-pfn_base) < max_mapnr))
> -
> -#define ARCH_PFN_OFFSET (pfn_base)
> + (((pfn) >= ARCH_PFN_OFFSET) && (((pfn) - ARCH_PFN_OFFSET) < max_mapnr))
>
> #endif /* __ASSEMBLY__ */
>
> @@ -115,8 +119,10 @@ extern unsigned long min_low_pfn;
> #include <asm-generic/memory_model.h>
> #include <asm-generic/getorder.h>
>
> +#ifdef CONFIG_MMU
> /* vDSO support */
> /* We do define AT_SYSINFO_EHDR but don't use the gate mechanism */
> #define __HAVE_ARCH_GATE_AREA
> +#endif /* CONFIG_MMU */
>
> #endif /* _ASM_RISCV_PAGE_H */
> diff --git a/arch/riscv/include/asm/pgalloc.h b/arch/riscv/include/asm/pgalloc.h
> index eb8b0195f27f..8d60c862d2f9 100644
> --- a/arch/riscv/include/asm/pgalloc.h
> +++ b/arch/riscv/include/asm/pgalloc.h
> @@ -10,6 +10,7 @@
> #include <linux/mm.h>
> #include <asm/tlb.h>
>
> +#ifdef CONFIG_MMU
> static inline void pmd_populate_kernel(struct mm_struct *mm,
> pmd_t *pmd, pte_t *pte)
> {
> @@ -106,6 +107,7 @@ do { \
> pgtable_page_dtor(pte); \
> tlb_remove_page((tlb), pte); \
> } while (0)
> +#endif /* CONFIG_MMU */
>
> static inline void check_pgt_cache(void)
> {
> diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
> index f7c3f7de15f2..dd6a63648e4a 100644
> --- a/arch/riscv/include/asm/pgtable.h
> +++ b/arch/riscv/include/asm/pgtable.h
> @@ -24,6 +24,7 @@
> #include <asm/pgtable-32.h>
> #endif /* CONFIG_64BIT */
>
> +#ifdef CONFIG_MMU
> /* Number of entries in the page global directory */
> #define PTRS_PER_PGD (PAGE_SIZE / sizeof(pgd_t))
> /* Number of entries in the page table */
> @@ -31,7 +32,6 @@
>
> /* Number of PGD entries that a user-mode program can use */
> #define USER_PTRS_PER_PGD (TASK_SIZE / PGDIR_SIZE)
> -#define FIRST_USER_ADDRESS 0
>
> /* Page protection bits */
> #define _PAGE_BASE (_PAGE_PRESENT | _PAGE_ACCESSED | _PAGE_USER)
> @@ -81,13 +81,6 @@ extern pgd_t swapper_pg_dir[];
> #define __S110 PAGE_SHARED_EXEC
> #define __S111 PAGE_SHARED_EXEC
>
> -/*
> - * ZERO_PAGE is a global shared page that is always zero,
> - * used for zero-mapped memory areas, etc.
> - */
> -extern unsigned long empty_zero_page[PAGE_SIZE / sizeof(unsigned long)];
> -#define ZERO_PAGE(vaddr) (virt_to_page(empty_zero_page))
> -
> static inline int pmd_present(pmd_t pmd)
> {
> return (pmd_val(pmd) & (_PAGE_PRESENT | _PAGE_PROT_NONE));
> @@ -392,6 +385,18 @@ static inline int ptep_clear_flush_young(struct vm_area_struct *vma,
> #define __pte_to_swp_entry(pte) ((swp_entry_t) { pte_val(pte) })
> #define __swp_entry_to_pte(x) ((pte_t) { (x).val })
>
> +#define VMALLOC_SIZE (KERN_VIRT_SIZE >> 1)
> +#define VMALLOC_END (PAGE_OFFSET - 1)
> +#define VMALLOC_START (PAGE_OFFSET - VMALLOC_SIZE)
> +
> +#else /* CONFIG_MMU */
> +
> +#define PAGE_KERNEL __pgprot(0)
> +#define swapper_pg_dir NULL
> +#define VMALLOC_START 0
> +
> +#endif /* CONFIG_MMU */
> +
> #ifdef CONFIG_FLATMEM
> #define kern_addr_valid(addr) (1) /* FIXME */
> #endif
> @@ -404,10 +409,7 @@ static inline void pgtable_cache_init(void)
> /* No page table caches to initialize */
> }
>
> -#define VMALLOC_SIZE (KERN_VIRT_SIZE >> 1)
> -#define VMALLOC_END (PAGE_OFFSET - 1)
> -#define VMALLOC_START (PAGE_OFFSET - VMALLOC_SIZE)
> -
> +#ifdef CONFIG_MMU
> /*
> * Task size is 0x40000000000 for RV64 or 0xb800000 for RV32.
> * Note that PGDIR_SIZE must evenly divide TASK_SIZE.
> @@ -417,6 +419,18 @@ static inline void pgtable_cache_init(void)
> #else
> #define TASK_SIZE VMALLOC_START
> #endif
> +#else /* CONFIG_MMU */
> +#define TASK_SIZE 0xffffffffUL
> +#endif /* !CONFIG_MMU */
> +
> +#define FIRST_USER_ADDRESS 0
> +
> +/*
> + * ZERO_PAGE is a global shared page that is always zero,
> + * used for zero-mapped memory areas, etc.
> + */
> +extern unsigned long empty_zero_page[PAGE_SIZE / sizeof(unsigned long)];
> +#define ZERO_PAGE(vaddr) (virt_to_page(empty_zero_page))
>
> #include <asm-generic/pgtable.h>
>
> diff --git a/arch/riscv/include/asm/tlbflush.h b/arch/riscv/include/asm/tlbflush.h
> index 687dd19735a7..f127b3d17ec2 100644
> --- a/arch/riscv/include/asm/tlbflush.h
> +++ b/arch/riscv/include/asm/tlbflush.h
> @@ -10,6 +10,7 @@
> #include <linux/mm_types.h>
> #include <asm/smp.h>
>
> +#ifdef CONFIG_MMU
> /*
> * Flush entire local TLB. 'sfence.vma' implicitly fences with the instruction
> * cache as well, so a 'fence.i' is not necessary.
> @@ -24,8 +25,12 @@ static inline void local_flush_tlb_page(unsigned long addr)
> {
> __asm__ __volatile__ ("sfence.vma %0" : : "r" (addr) : "memory");
> }
> +#else /* CONFIG_MMU */
> +#define local_flush_tlb_all() do { } while (0)
> +#define local_flush_tlb_page(addr) do { } while (0)
> +#endif /* CONFIG_MMU */
>
> -#ifndef CONFIG_SMP
> +#if !defined(CONFIG_SMP) || !defined(CONFIG_MMU)
>
> #define flush_tlb_all() local_flush_tlb_all()
> #define flush_tlb_page(vma, addr) local_flush_tlb_page(addr)
> diff --git a/arch/riscv/include/asm/uaccess.h b/arch/riscv/include/asm/uaccess.h
> index e076437cfafe..f462a183a9c2 100644
> --- a/arch/riscv/include/asm/uaccess.h
> +++ b/arch/riscv/include/asm/uaccess.h
> @@ -11,6 +11,7 @@
> /*
> * User space memory access functions
> */
> +#ifdef CONFIG_MMU
> #include <linux/errno.h>
> #include <linux/compiler.h>
> #include <linux/thread_info.h>
> @@ -475,4 +476,7 @@ unsigned long __must_check clear_user(void __user *to, unsigned long n)
> __ret; \
> })
>
> +#else /* CONFIG_MMU */
> +#include <asm-generic/uaccess.h>
> +#endif /* CONFIG_MMU */
> #endif /* _ASM_RISCV_UACCESS_H */
> diff --git a/arch/riscv/kernel/Makefile b/arch/riscv/kernel/Makefile
> index f933c04f89db..d720666283d6 100644
> --- a/arch/riscv/kernel/Makefile
> +++ b/arch/riscv/kernel/Makefile
> @@ -25,9 +25,8 @@ obj-y += time.o
> obj-y += traps.o
> obj-y += riscv_ksyms.o
> obj-y += stacktrace.o
> -obj-y += vdso.o
> obj-y += cacheinfo.o
> -obj-y += vdso/
> +obj-$(CONFIG_MMU) += vdso.o vdso/
>
> obj-$(CONFIG_M_MODE) += clint.o
> obj-$(CONFIG_FPU) += fpu.o
> diff --git a/arch/riscv/kernel/entry.S b/arch/riscv/kernel/entry.S
> index 18eeb1eec9d5..953c64b0b2b9 100644
> --- a/arch/riscv/kernel/entry.S
> +++ b/arch/riscv/kernel/entry.S
> @@ -370,6 +370,10 @@ ENTRY(__switch_to)
> ret
> ENDPROC(__switch_to)
>
> +#ifndef CONFIG_MMU
> +#define do_page_fault do_trap_unknown
> +#endif
> +
> .section ".rodata"
> /* Exception vector table */
> ENTRY(excp_vect_table)
> @@ -391,3 +395,10 @@ ENTRY(excp_vect_table)
> RISCV_PTR do_page_fault /* store page fault */
> excp_vect_table_end:
> END(excp_vect_table)
> +
> +#ifndef CONFIG_MMU
> +ENTRY(__user_rt_sigreturn)
> + li a7, __NR_rt_sigreturn
> + scall
> +END(__user_rt_sigreturn)
> +#endif
> diff --git a/arch/riscv/kernel/head.S b/arch/riscv/kernel/head.S
> index e05379fd8b64..d869cc7c6a12 100644
> --- a/arch/riscv/kernel/head.S
> +++ b/arch/riscv/kernel/head.S
> @@ -68,10 +68,12 @@ clear_bss_done:
> la a2, boot_cpu_hartid
> REG_S a0, (a2)
>
> +#ifdef CONFIG_MMU
> /* Initialize page tables and relocate to virtual addresses */
> la sp, init_thread_union + THREAD_SIZE
> call setup_vm
> call relocate
> +#endif /* CONFIG_MMU */
>
> /* Restore C environment */
> la tp, init_task
> @@ -83,6 +85,7 @@ clear_bss_done:
> call parse_dtb
> tail start_kernel
>
> +#ifdef CONFIG_MMU
> relocate:
> /* Relocate return address */
> li a1, PAGE_OFFSET
> @@ -134,6 +137,7 @@ relocate:
> sfence.vma
>
> ret
> +#endif /* CONFIG_MMU */
>
> .Lsecondary_start:
> #ifdef CONFIG_SMP
> @@ -162,8 +166,10 @@ relocate:
> beqz tp, .Lwait_for_cpu_up
> fence
>
> +#ifdef CONFIG_MMU
> /* Enable virtual memory and relocate to virtual address */
> call relocate
> +#endif
>
> tail smp_callin
> #endif
> diff --git a/arch/riscv/kernel/signal.c b/arch/riscv/kernel/signal.c
> index dfb26b64e17a..7de7e539b25b 100644
> --- a/arch/riscv/kernel/signal.c
> +++ b/arch/riscv/kernel/signal.c
> @@ -17,11 +17,16 @@
> #include <asm/switch_to.h>
> #include <asm/csr.h>
>
> +extern u32 __user_rt_sigreturn[2];
> +
> #define DEBUG_SIG 0
>
> struct rt_sigframe {
> struct siginfo info;
> struct ucontext uc;
> +#ifndef CONFIG_MMU
> + u32 sigreturn_code[2];
> +#endif
> };
>
> #ifdef CONFIG_FPU
> @@ -166,7 +171,6 @@ static inline void __user *get_sigframe(struct ksignal *ksig,
> return (void __user *)sp;
> }
>
> -
> static int setup_rt_frame(struct ksignal *ksig, sigset_t *set,
> struct pt_regs *regs)
> {
> @@ -189,8 +193,19 @@ static int setup_rt_frame(struct ksignal *ksig, sigset_t *set,
> return -EFAULT;
>
> /* Set up to return from userspace. */
> +#ifdef CONFIG_MMU
> regs->ra = (unsigned long)VDSO_SYMBOL(
> current->mm->context.vdso, rt_sigreturn);
> +#else
> + /*
> + * For the nommu case we don't have a VDSO. Instead we push two
> + * instructions to call the rt_sigreturn syscall onto the user stack.
> + */
> + if (copy_to_user(&frame->sigreturn_code, __user_rt_sigreturn,
> + sizeof(frame->sigreturn_code)))
> + return -EFAULT;
> + regs->ra = (unsigned long)&frame->sigreturn_code;;
> +#endif /* CONFIG_MMU */
>
> /*
> * Set up registers for signal handler.
> diff --git a/arch/riscv/lib/Makefile b/arch/riscv/lib/Makefile
> index 8e364ebf37de..5382e42d0cba 100644
> --- a/arch/riscv/lib/Makefile
> +++ b/arch/riscv/lib/Makefile
> @@ -2,8 +2,6 @@
> lib-y += delay.o
> lib-y += memcpy.o
> lib-y += memset.o
> -lib-y += uaccess.o
> -
> -lib-$(CONFIG_64BIT) += tishift.o
> -
> -lib-$(CONFIG_32BIT) += udivdi3.o
> +lib-$(CONFIG_MMU) += uaccess.o
> +lib-$(CONFIG_64BIT) += tishift.o
> +lib-$(CONFIG_32BIT) += udivdi3.o
> diff --git a/arch/riscv/mm/Makefile b/arch/riscv/mm/Makefile
> index fc51d3b7876e..8fc2fd148b06 100644
> --- a/arch/riscv/mm/Makefile
> +++ b/arch/riscv/mm/Makefile
> @@ -6,9 +6,8 @@ CFLAGS_REMOVE_init.o = -pg
> endif
>
> obj-y += init.o
> -obj-y += fault.o
> obj-y += extable.o
> -obj-y += ioremap.o
> +obj-$(CONFIG_MMU) += fault.o ioremap.o
> obj-y += cacheflush.o
> obj-y += context.o
> obj-y += sifive_l2_cache.o
> diff --git a/arch/riscv/mm/cacheflush.c b/arch/riscv/mm/cacheflush.c
> index 10875ea1065e..0fc69eedc921 100644
> --- a/arch/riscv/mm/cacheflush.c
> +++ b/arch/riscv/mm/cacheflush.c
> @@ -90,6 +90,7 @@ void flush_icache_mm(struct mm_struct *mm, bool local)
>
> #endif /* CONFIG_SMP */
>
> +#ifdef CONFIG_MMU
> void flush_icache_pte(pte_t pte)
> {
> struct page *page = pte_page(pte);
> @@ -97,3 +98,4 @@ void flush_icache_pte(pte_t pte)
> if (!test_and_set_bit(PG_dcache_clean, &page->flags))
> flush_icache_all();
> }
> +#endif /* CONFIG_MMU */
> diff --git a/arch/riscv/mm/context.c b/arch/riscv/mm/context.c
> index beeb5d7f92ea..073ff12a838a 100644
> --- a/arch/riscv/mm/context.c
> +++ b/arch/riscv/mm/context.c
> @@ -57,8 +57,10 @@ void switch_mm(struct mm_struct *prev, struct mm_struct *next,
> cpumask_clear_cpu(cpu, mm_cpumask(prev));
> cpumask_set_cpu(cpu, mm_cpumask(next));
>
> +#ifdef CONFIG_MMU
> csr_write(CSR_SATP, virt_to_pfn(next->pgd) | SATP_MODE);
> local_flush_tlb_all();
> +#endif
>
> flush_icache_deferred(next);
> }
> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
> index 84747d7a1e85..782be273e714 100644
> --- a/arch/riscv/mm/init.c
> +++ b/arch/riscv/mm/init.c
> @@ -142,6 +142,7 @@ void __init setup_bootmem(void)
> }
> }
>
> +#ifdef CONFIG_MMU
> unsigned long va_pa_offset;
> EXPORT_SYMBOL(va_pa_offset);
> unsigned long pfn_base;
> @@ -247,3 +248,4 @@ asmlinkage void __init setup_vm(void)
> __pgprot(_PAGE_TABLE));
> #endif
> }
> +#endif /* CONFIG_MMU */
>
--
Thanks,
David / dhildenb
