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Date:   Wed, 18 Mar 2020 18:45:09 -0700 (PDT)
Subject:     Re: [PATCH 1/2] riscv: uaccess should be used in nommu mode
In-Reply-To: <20200303093418.9180-1-greentime.hu@sifive.com>
CC:     green.hu@gmail.com, greentime@kernel.org,
        Paul Walmsley <paul.walmsley@sifive.com>,
        linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org,
        greentime.hu@sifive.com
From:   Palmer Dabbelt <palmer@dabbelt.com>
To:     greentime.hu@sifive.com
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On Tue, 03 Mar 2020 01:34:17 PST (-0800), greentime.hu@sifive.com wrote:
> It might have the unaligned access exception when trying to exchange data
> with user space program. In this case, it failed in tty_ioctl(). Therefore
> we should enable uaccess.S for NOMMU mode since the generic code doesn't
> handle the unaligned access cases.
>
>    0x8013a212 <tty_ioctl+462>:  ld      a5,460(s1)
>
> [    0.115279] Oops - load address misaligned [#1]
> [    0.115284] CPU: 0 PID: 29 Comm: sh Not tainted 5.4.0-rc5-00020-gb4c27160d562-dirty #36
> [    0.115294] epc: 000000008013a212 ra : 000000008013a212 sp : 000000008f48dd50
> [    0.115303]  gp : 00000000801cac28 tp : 000000008fb80000 t0 : 00000000000000e8
> [    0.115312]  t1 : 000000008f58f108 t2 : 0000000000000009 s0 : 000000008f48ddf0
> [    0.115321]  s1 : 000000008f8c6220 a0 : 0000000000000001 a1 : 000000008f48dd28
> [    0.115330]  a2 : 000000008fb80000 a3 : 00000000801a7398 a4 : 0000000000000000
> [    0.115339]  a5 : 0000000000000000 a6 : 000000008f58f0c6 a7 : 000000000000001d
> [    0.115348]  s2 : 000000008f8c6308 s3 : 000000008f78b7c8 s4 : 000000008fb834c0
> [    0.115357]  s5 : 0000000000005413 s6 : 0000000000000000 s7 : 000000008f58f2b0
> [    0.115366]  s8 : 000000008f858008 s9 : 000000008f776818 s10: 000000008f776830
> [    0.115375]  s11: 000000008fb840a8 t3 : 1999999999999999 t4 : 000000008f78704c
> [    0.115384]  t5 : 0000000000000005 t6 : 0000000000000002
> [    0.115391] status: 0000000200001880 badaddr: 000000008f8c63ec cause: 0000000000000004
> [    0.115401] ---[ end trace 00d490c6a8b6c9ac ]---
>
> This failure could be fixed after this patch applied.
>
> [    0.002282] Run /init as init process
> Initializing random number generator... [    0.005573] random: dd: uninitialized urandom read (512 bytes read)
> done.
>
> Welcome to Buildroot
> buildroot login: root
> Password:
> Jan  1 00:00:00 login[62]: root login on 'ttySIF0'
> ~ #
>
> Signed-off-by: Greentime Hu <greentime.hu@sifive.com>
> ---
>  arch/riscv/Kconfig               |  1 -
>  arch/riscv/include/asm/uaccess.h | 36 ++++++++++++++++----------------
>  arch/riscv/lib/Makefile          |  2 +-
>  3 files changed, 19 insertions(+), 20 deletions(-)
>
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index 73f029eae0cc..92d63a63aec8 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -50,7 +50,6 @@ config RISCV
>  	select PCI_DOMAINS_GENERIC if PCI
>  	select PCI_MSI if PCI
>  	select RISCV_TIMER
> -	select UACCESS_MEMCPY if !MMU
>  	select GENERIC_IRQ_MULTI_HANDLER
>  	select GENERIC_ARCH_TOPOLOGY if SMP
>  	select ARCH_HAS_PTE_SPECIAL
> diff --git a/arch/riscv/include/asm/uaccess.h b/arch/riscv/include/asm/uaccess.h
> index f462a183a9c2..8ce9d607b53d 100644
> --- a/arch/riscv/include/asm/uaccess.h
> +++ b/arch/riscv/include/asm/uaccess.h
> @@ -11,6 +11,24 @@
>  /*
>   * User space memory access functions
>   */
> +
> +extern unsigned long __must_check __asm_copy_to_user(void __user *to,
> +	const void *from, unsigned long n);
> +extern unsigned long __must_check __asm_copy_from_user(void *to,
> +	const void __user *from, unsigned long n);
> +
> +static inline unsigned long
> +raw_copy_from_user(void *to, const void __user *from, unsigned long n)
> +{
> +	return __asm_copy_from_user(to, from, n);
> +}
> +
> +static inline unsigned long
> +raw_copy_to_user(void __user *to, const void *from, unsigned long n)
> +{
> +	return __asm_copy_to_user(to, from, n);
> +}
> +
>  #ifdef CONFIG_MMU
>  #include <linux/errno.h>
>  #include <linux/compiler.h>
> @@ -367,24 +385,6 @@ do {								\
>  		-EFAULT;					\
>  })
>
> -
> -extern unsigned long __must_check __asm_copy_to_user(void __user *to,
> -	const void *from, unsigned long n);
> -extern unsigned long __must_check __asm_copy_from_user(void *to,
> -	const void __user *from, unsigned long n);
> -
> -static inline unsigned long
> -raw_copy_from_user(void *to, const void __user *from, unsigned long n)
> -{
> -	return __asm_copy_from_user(to, from, n);
> -}
> -
> -static inline unsigned long
> -raw_copy_to_user(void __user *to, const void *from, unsigned long n)
> -{
> -	return __asm_copy_to_user(to, from, n);
> -}
> -
>  extern long strncpy_from_user(char *dest, const char __user *src, long count);
>
>  extern long __must_check strlen_user(const char __user *str);
> diff --git a/arch/riscv/lib/Makefile b/arch/riscv/lib/Makefile
> index 47e7a8204460..0d0db80800c4 100644
> --- a/arch/riscv/lib/Makefile
> +++ b/arch/riscv/lib/Makefile
> @@ -2,5 +2,5 @@
>  lib-y			+= delay.o
>  lib-y			+= memcpy.o
>  lib-y			+= memset.o
> -lib-$(CONFIG_MMU)	+= uaccess.o
> +lib-y			+= uaccess.o
>  lib-$(CONFIG_64BIT)	+= tishift.o

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