Re: [PATCH v12 1/6] uaccess: add generic fallback version of copy_mc_to_user()

Jonathan Cameron
2024-08-19T09:57:55Z

On Tue, 28 May 2024 16:59:10 +0800
Tong Tiangen <tongtiangen@huawei.com> wrote:

> x86/powerpc has it's implementation of copy_mc_to_user(), we add generic
> fallback in include/linux/uaccess.h prepare for other architechures to
> enable CONFIG_ARCH_HAS_COPY_MC.
>
> Signed-off-by: Tong Tiangen <tongtiangen@huawei.com>
> Acked-by: Michael Ellerman <mpe@ellerman.id.au>
Seems like a sensible approach to me given existing fallbacks in x86
if the relevant features are disabled.

It may be worth exploring at some point if some of the special casing
in the callers of this function can also be remove now there
is a default version. There are some small differences but I've
not analyzed if they matter or not.

Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

> ---
> arch/powerpc/include/asm/uaccess.h | 1 +
> arch/x86/include/asm/uaccess.h | 1 +
> include/linux/uaccess.h | 8 ++++++++
> 3 files changed, 10 insertions(+)
>
> diff --git a/arch/powerpc/include/asm/uaccess.h b/arch/powerpc/include/asm/uaccess.h
> index de10437fd206..df42e6ad647f 100644
> --- a/arch/powerpc/include/asm/uaccess.h
> +++ b/arch/powerpc/include/asm/uaccess.h
> @@ -381,6 +381,7 @@ copy_mc_to_user(void __user *to, const void *from, unsigned long n)
>
> return n;
> }
> +#define copy_mc_to_user copy_mc_to_user
> #endif
>
> extern long __copy_from_user_flushcache(void *dst, const void __user *src,
> diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h
> index 0f9bab92a43d..309f2439327e 100644
> --- a/arch/x86/include/asm/uaccess.h
> +++ b/arch/x86/include/asm/uaccess.h
> @@ -497,6 +497,7 @@ copy_mc_to_kernel(void *to, const void *from, unsigned len);
>
> unsigned long __must_check
> copy_mc_to_user(void __user *to, const void *from, unsigned len);
> +#define copy_mc_to_user copy_mc_to_user
> #endif
>
> /*
> diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h
> index 3064314f4832..0dfa9241b6ee 100644
> --- a/include/linux/uaccess.h
> +++ b/include/linux/uaccess.h
> @@ -205,6 +205,14 @@ copy_mc_to_kernel(void *dst, const void *src, size_t cnt)
> }
> #endif
>
> +#ifndef copy_mc_to_user
> +static inline unsigned long __must_check
> +copy_mc_to_user(void *dst, const void *src, size_t cnt)
> +{
> + return copy_to_user(dst, src, cnt);
> +}
> +#endif
> +
> static __always_inline void pagefault_disabled_inc(void)
> {
> current->pagefault_disabled++;