Re: [PATCH v4 3/7] vmalloc: Add text_alloc() and text_free()

[Mike Rapoport]

On Fri, Jul 17, 2020 at 06:04:17AM +0300, Jarkko Sakkinen wrote:
> Introduce functions for allocating memory for dynamic trampolines, such
> as kprobes. An arch can promote the availability of these functions with
> CONFIG_ARCH_HAS_TEXT_ALLOC. Provide default/fallback implementation
> wrapping module_alloc() and module_memfree().
> 
> Cc: Andi Kleen <ak@xxxxxxxxxxxxxxx>
> Cc: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
> Suggested-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@xxxxxxxxxxxxxxx>
> ---
>  include/linux/vmalloc.h | 23 +++++++++++++++++++++++
>  1 file changed, 23 insertions(+)
> 
> diff --git a/include/linux/vmalloc.h b/include/linux/vmalloc.h
> index 0221f852a7e1..e981436e30b6 100644
> --- a/include/linux/vmalloc.h
> +++ b/include/linux/vmalloc.h
> @@ -9,6 +9,7 @@
>  #include <asm/page.h>		/* pgprot_t */
>  #include <linux/rbtree.h>
>  #include <linux/overflow.h>
> +#include <linux/moduleloader.h>
>  
>  #include <asm/vmalloc.h>
>  
> @@ -249,4 +250,26 @@ pcpu_free_vm_areas(struct vm_struct **vms, int nr_vms)
>  int register_vmap_purge_notifier(struct notifier_block *nb);
>  int unregister_vmap_purge_notifier(struct notifier_block *nb);
>  
> +#ifdef CONFIG_ARCH_HAS_TEXT_ALLOC
> +/*
> + * Allocate memory to be used for dynamic trampoline code.
> + */
> +void *text_alloc(unsigned long size);
> +
> +/*
> + * Free memory returned from text_alloc().
> + */
> +void text_free(void *region);
> +#else
> +static inline void *text_alloc(unsigned long size)
> +{
> +	return module_alloc(size);
> +}
> +
> +static inline void text_free(void *region)
> +{
> +	module_memfree(region);
> +}

Using module_alloc() as the default implementation of generic
text_alloc() does not sound right to me.

I would suggest rename module_alloc() to text_alloc() on x86, as Peter
proposed and then add text_alloc_kprobes() that can be overridden by the
architectures. x86 could use text_alloc(), arm64 vmalloc() with options
of their choice and the fallback would remain module_alloc(). Something
like (untested) patch below: