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

[Palmer Dabbelt]

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?