Re: [PATCH 8/8] riscv: remove address space overrides using set_fs()

[Palmer Dabbelt <palmer@dabbelt.com>]

On Sun, 06 Sep 2020 22:58:25 PDT (-0700), Christoph Hellwig wrote:
> Stop providing the possibility to override the address space using
> set_fs() now that there is no need for that any more.
>
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  arch/riscv/Kconfig                   |  1 -
>  arch/riscv/include/asm/thread_info.h |  6 ------
>  arch/riscv/include/asm/uaccess.h     | 27 +--------------------------
>  arch/riscv/kernel/process.c          |  1 -
>  4 files changed, 1 insertion(+), 34 deletions(-)
>
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index 460e3971a80fde..33dde87218ddab 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -86,7 +86,6 @@ config RISCV
>  	select SPARSE_IRQ
>  	select SYSCTL_EXCEPTION_TRACE
>  	select THREAD_INFO_IN_TASK
> -	select SET_FS
>  	select UACCESS_MEMCPY if !MMU
>
>  config ARCH_MMAP_RND_BITS_MIN
> diff --git a/arch/riscv/include/asm/thread_info.h b/arch/riscv/include/asm/thread_info.h
> index 464a2bbc97ea33..a390711129de64 100644
> --- a/arch/riscv/include/asm/thread_info.h
> +++ b/arch/riscv/include/asm/thread_info.h
> @@ -24,10 +24,6 @@
>  #include <asm/processor.h>
>  #include <asm/csr.h>
>
> -typedef struct {
> -	unsigned long seg;
> -} mm_segment_t;
> -
>  /*
>   * low level task data that entry.S needs immediate access to
>   * - this struct should fit entirely inside of one cache line
> @@ -39,7 +35,6 @@ typedef struct {
>  struct thread_info {
>  	unsigned long		flags;		/* low level flags */
>  	int                     preempt_count;  /* 0=>preemptible, <0=>BUG */
> -	mm_segment_t		addr_limit;
>  	/*
>  	 * These stack pointers are overwritten on every system call or
>  	 * exception.  SP is also saved to the stack it can be recovered when
> @@ -59,7 +54,6 @@ struct thread_info {
>  {						\
>  	.flags		= 0,			\
>  	.preempt_count	= INIT_PREEMPT_COUNT,	\
> -	.addr_limit	= KERNEL_DS,		\
>  }
>
>  #endif /* !__ASSEMBLY__ */
> diff --git a/arch/riscv/include/asm/uaccess.h b/arch/riscv/include/asm/uaccess.h
> index 264e52fb62b143..c47e6b35c551f4 100644
> --- a/arch/riscv/include/asm/uaccess.h
> +++ b/arch/riscv/include/asm/uaccess.h
> @@ -26,29 +26,6 @@
>  #define __disable_user_access()							\
>  	__asm__ __volatile__ ("csrc sstatus, %0" : : "r" (SR_SUM) : "memory")
>
> -/*
> - * The fs value determines whether argument validity checking should be
> - * performed or not.  If get_fs() == USER_DS, checking is performed, with
> - * get_fs() == KERNEL_DS, checking is bypassed.
> - *
> - * For historical reasons, these macros are grossly misnamed.
> - */
> -
> -#define MAKE_MM_SEG(s)	((mm_segment_t) { (s) })
> -
> -#define KERNEL_DS	MAKE_MM_SEG(~0UL)
> -#define USER_DS		MAKE_MM_SEG(TASK_SIZE)
> -
> -#define get_fs()	(current_thread_info()->addr_limit)
> -
> -static inline void set_fs(mm_segment_t fs)
> -{
> -	current_thread_info()->addr_limit = fs;
> -}
> -
> -#define uaccess_kernel() (get_fs().seg == KERNEL_DS.seg)
> -#define user_addr_max()	(get_fs().seg)
> -
>  /**
>   * access_ok: - Checks if a user space pointer is valid
>   * @addr: User space pointer to start of block to check
> @@ -76,9 +53,7 @@ static inline void set_fs(mm_segment_t fs)
>   */
>  static inline int __access_ok(unsigned long addr, unsigned long size)
>  {
> -	const mm_segment_t fs = get_fs();
> -
> -	return size <= fs.seg && addr <= fs.seg - size;
> +	return size <= TASK_SIZE && addr <= TASK_SIZE - size;
>  }
>
>  /*
> diff --git a/arch/riscv/kernel/process.c b/arch/riscv/kernel/process.c
> index 2b97c493427c9e..19225ec65db62f 100644
> --- a/arch/riscv/kernel/process.c
> +++ b/arch/riscv/kernel/process.c
> @@ -84,7 +84,6 @@ void start_thread(struct pt_regs *regs, unsigned long pc,
>  	}
>  	regs->epc = pc;
>  	regs->sp = sp;
> -	set_fs(USER_DS);
>  }
>
>  void flush_thread(void)

Reviewed-by: Palmer Dabbelt <palmerdabbelt@google.com>
Acked-by: Palmer Dabbelt <palmerdabbelt@google.com>