Re: [PATCH 1/2] kdump: vmcore: move copy_to() from vmcore.c to uaccess.h

[Andrew Morton]

On Fri, 10 Dec 2021 21:36:00 +0800 Tiezhu Yang <yangtiezhu@xxxxxxxxxxx> wrote:

> In arch/*/kernel/crash_dump*.c, there exist similar code about
> copy_oldmem_page(), move copy_to() from vmcore.c to uaccess.h,
> and then we can use copy_to() to simplify the related code.
> 
> ...
>
> --- a/fs/proc/vmcore.c
> +++ b/fs/proc/vmcore.c
> @@ -238,20 +238,6 @@ copy_oldmem_page_encrypted(unsigned long pfn, char *buf, size_t csize,
>  	return copy_oldmem_page(pfn, buf, csize, offset, userbuf);
>  }
>  
> -/*
> - * Copy to either kernel or user space
> - */
> -static int copy_to(void *target, void *src, size_t size, int userbuf)
> -{
> -	if (userbuf) {
> -		if (copy_to_user((char __user *) target, src, size))
> -			return -EFAULT;
> -	} else {
> -		memcpy(target, src, size);
> -	}
> -	return 0;
> -}
> -
>  #ifdef CONFIG_PROC_VMCORE_DEVICE_DUMP
>  static int vmcoredd_copy_dumps(void *dst, u64 start, size_t size, int userbuf)
>  {
> diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h
> index ac03940..4a6c3e4 100644
> --- a/include/linux/uaccess.h
> +++ b/include/linux/uaccess.h
> @@ -201,6 +201,20 @@ copy_to_user(void __user *to, const void *from, unsigned long n)
>  	return n;
>  }
>  
> +/*
> + * Copy to either kernel or user space
> + */
> +static inline int copy_to(void *target, void *src, size_t size, int userbuf)
> +{
> +	if (userbuf) {
> +		if (copy_to_user((char __user *) target, src, size))
> +			return -EFAULT;
> +	} else {
> +		memcpy(target, src, size);
> +	}
> +	return 0;
> +}
> +

Ordinarily I'd say "this is too large to be inlined".  But the function
has only a single callsite per architecture so inlining it won't cause
bloat at present.

But hopefully copy_to() will get additional callers in the future, in
which case it shouldn't be inlined.  So I'm thinking it would be best
to start out with this as a regular non-inlined function, in
lib/usercopy.c.

Also, copy_to() is a very poor name for a globally-visible helper
function.  Better would be copy_to_user_or_kernel(), although that's
perhaps a bit long.

And the `userbuf' arg should have type bool, yes?