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| author | Christoph Hellwig <hch@lst.de> | 2019-10-28 13:10:41 +0100 |
|---|---|---|
| committer | Paul Walmsley <paul.walmsley@sifive.com> | 2019-11-17 15:17:39 -0800 |
| commit | 6bd33e1ece528f67646db33bf97406b747dafda0 (patch) | |
| tree | f78c5001071a475fa5bed9781c07a609118684f7 /arch/riscv/kernel/head.S | |
| parent | 9e80635619b51ddc56bdeca4da4056eb7a2a77e0 (diff) | |
| download | linux-6bd33e1ece528f67646db33bf97406b747dafda0.tar.gz | |
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: Christoph Hellwig <hch@lst.de>
Reviewed-by: Anup 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: Paul Walmsley <paul.walmsley@sifive.com>
Diffstat (limited to 'arch/riscv/kernel/head.S')
| -rw-r--r-- | arch/riscv/kernel/head.S | 6 |
1 files changed, 6 insertions, 0 deletions
diff --git a/arch/riscv/kernel/head.S b/arch/riscv/kernel/head.S index 64eb8beb228e..84a6f0a4b120 100644 --- a/arch/riscv/kernel/head.S +++ b/arch/riscv/kernel/head.S @@ -109,8 +109,10 @@ clear_bss_done: la sp, init_thread_union + THREAD_SIZE mv a0, s1 call setup_vm +#ifdef CONFIG_MMU la a0, early_pg_dir call relocate +#endif /* CONFIG_MMU */ /* Restore C environment */ la tp, init_task @@ -121,6 +123,7 @@ clear_bss_done: call parse_dtb tail start_kernel +#ifdef CONFIG_MMU relocate: /* Relocate return address */ li a1, PAGE_OFFSET @@ -171,6 +174,7 @@ relocate: sfence.vma ret +#endif /* CONFIG_MMU */ .Lsecondary_start: #ifdef CONFIG_SMP @@ -196,9 +200,11 @@ relocate: beqz tp, .Lwait_for_cpu_up fence +#ifdef CONFIG_MMU /* Enable virtual memory and relocate to virtual address */ la a0, swapper_pg_dir call relocate +#endif tail smp_callin #endif |