Re: [PATCH] RISC-V: Load modules within relative jump range of the kernel text.

[Shea Levy]

Hi Palmer,

Palmer Dabbelt <palmer@xxxxxxxxxx> writes:

> On Sun, 22 Apr 2018 05:53:56 PDT (-0700), shea@xxxxxxxxxxxx wrote:
>> Hi Palmer,
>>
>> Shea Levy <shea@xxxxxxxxxxxx> writes:
>>
>>> Signed-off-by: Shea Levy <shea@xxxxxxxxxxxx>
>>> ---
>>>
>>> Note that this patch worked in my old modules patchset and seems to be
>>> working now, but my kernel boot locks up on top of
>>> riscv-for-linus-4.17-mw0 and I don't know if it's due to this patch or
>>> something else that's changed in the mean time.
>>>
>>> ---
>>>  arch/riscv/include/asm/pgtable.h |  9 +++++++++
>>>  arch/riscv/kernel/module.c       | 11 +++++++++++
>>>  2 files changed, 20 insertions(+)
>>>
>>> diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
>>> index 16301966d65b..b08ded13364a 100644
>>> --- a/arch/riscv/include/asm/pgtable.h
>>> +++ b/arch/riscv/include/asm/pgtable.h
>>> @@ -25,6 +25,7 @@
>>>  #include <asm/page.h>
>>>  #include <asm/tlbflush.h>
>>>  #include <linux/mm_types.h>
>>> +#include <linux/sizes.h>
>>>  
>>>  #ifdef CONFIG_64BIT
>>>  #include <asm/pgtable-64.h>
>>> @@ -425,6 +426,14 @@ static inline void pgtable_cache_init(void)
>>>  #define TASK_SIZE VMALLOC_START
>>>  #endif
>>>  
>>> +/*
>>> + * The module space lives between the addresses given by TASK_SIZE
>>> + * and PAGE_OFFSET - it must be within 2G of the kernel text.
>>> + */
>>> +#define MODULES_SIZE		(SZ_128M)
>>> +#define MODULES_VADDR		(PAGE_OFFSET - MODULES_SIZE)
>>> +#define MODULES_END		(VMALLOC_END)
>>> +
>>>  #include <asm-generic/pgtable.h>
>>>  
>>>  #endif /* !__ASSEMBLY__ */
>>> diff --git a/arch/riscv/kernel/module.c b/arch/riscv/kernel/module.c
>>> index 5dddba301d0a..1b382c7de095 100644
>>> --- a/arch/riscv/kernel/module.c
>>> +++ b/arch/riscv/kernel/module.c
>>> @@ -16,6 +16,8 @@
>>>  #include <linux/err.h>
>>>  #include <linux/errno.h>
>>>  #include <linux/moduleloader.h>
>>> +#include <linux/vmalloc.h>
>>> +#include <asm/pgtable.h>
>>>  
>>>  static int apply_r_riscv_64_rela(struct module *me, u32 *location, Elf_Addr v)
>>>  {
>>> @@ -382,3 +384,12 @@ int apply_relocate_add(Elf_Shdr *sechdrs, const char *strtab,
>>>  
>>>  	return 0;
>>>  }
>>> +
>>> +void *module_alloc(unsigned long size)
>>> +{
>>> +	return __vmalloc_node_range(size, 1, MODULES_VADDR,
>>> +				    MODULES_END, GFP_KERNEL,
>>> +				    PAGE_KERNEL_EXEC, 0,
>>> +				    NUMA_NO_NODE,
>>> +				    __builtin_return_address(0));
>>> +}
>>> -- 
>>> 2.16.2
>>
>> Any thoughts on this?
>
> The concept looks good, but does this actually keep the modules within 2GiB of 
> the text if PAGE_OFFSET is large?

It's been some time since I wrote this, but I thought PAGE_OFFSET was
where the kernel text *started*? So unless the text itself is bigger
than 2G - 128 M, in which case we're SOL anyway, it seems like this
should work. Is there something better we can do, without a large memory
model?

Thanks,
Shea

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