Re: [PATCH v1 03/15] powerpc/uaccess: Remove __get/put_user_inatomic()

Daniel Axtens
2021-03-02T07:32:04Z

Christophe Leroy <christophe.leroy@csgroup.eu> writes:

> Since commit 662bbcb2747c ("mm, sched: Allow uaccess in atomic with
> pagefault_disable()"), __get/put_user() can be used in atomic parts
> of the code, therefore the __get/put_user_inatomic() introduced
> by commit e68c825bb016 ("[POWERPC] Add inatomic versions of __get_user
> and __put_user") have become useless.

I spent some time chasing these macro definitions.

Let me see if I understand you.

__get_user(x, ptr) becomes __get_user_nocheck(..., true)
__get_user_inatomic() become __get_user_nosleep()

The difference between how __get_user_nosleep() and
__get_user_nocheck(..., true) operate is that __get_user_nocheck calls
might_fault() and __get_user_nosleep() does not.

If I understand the commit you reference and mm/memory.c, you're saying
that we can indeed call might_fault() when page faults are disabled,
because __might_fault() checks if page faults are disabled and does not
fire a warning if it is called with page faults disabled.

Therefore, it is safe to remove our _inatomic version that does not call
might_fault and just to call might_fault unconditionally.

Is that right?

I haven't checked changes you made to the various .c files in fine
detail but they appear to be entirely mechanical.

> powerpc is the only one having such functions. There is a real
> intention not to have to provide such _inatomic() helpers, see the
> comment in might_fault() in mm/memory.c introduced by
> commit 3ee1afa308f2 ("x86: some lock annotations for user
> copy paths, v2"):
>
> /*
> * it would be nicer only to annotate paths which are not under
> * pagefault_disable, however that requires a larger audit and
> * providing helpers like get_user_atomic.
> */
>

I'm not fully sure I understand what you're saying in this part of the
commit message.

Kind regards,
Daniel

>
> Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
> ---
> arch/powerpc/include/asm/uaccess.h | 37 -------------------
> arch/powerpc/kernel/align.c | 32 ++++++++--------
> .../kernel/hw_breakpoint_constraints.c | 2 +-
> arch/powerpc/kernel/traps.c | 2 +-
> 4 files changed, 18 insertions(+), 55 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/uaccess.h b/arch/powerpc/include/asm/uaccess.h
> index a08c482b1315..01aea0df4dd0 100644
> --- a/arch/powerpc/include/asm/uaccess.h
> +++ b/arch/powerpc/include/asm/uaccess.h
> @@ -53,11 +53,6 @@ static inline bool __access_ok(unsigned long addr, unsigned long size)
> #define __put_user(x, ptr) \
> __put_user_nocheck((__typeof__(*(ptr)))(x), (ptr), sizeof(*(ptr)))
>
> -#define __get_user_inatomic(x, ptr) \
> - __get_user_nosleep((x), (ptr), sizeof(*(ptr)))
> -#define __put_user_inatomic(x, ptr) \
> - __put_user_nosleep((__typeof__(*(ptr)))(x), (ptr), sizeof(*(ptr)))
> -
> #ifdef CONFIG_PPC64
>
> #define ___get_user_instr(gu_op, dest, ptr) \
> @@ -92,9 +87,6 @@ static inline bool __access_ok(unsigned long addr, unsigned long size)
> #define __get_user_instr(x, ptr) \
> ___get_user_instr(__get_user, x, ptr)
>
> -#define __get_user_instr_inatomic(x, ptr) \
> - ___get_user_instr(__get_user_inatomic, x, ptr)
> -
> extern long __put_user_bad(void);
>
> #define __put_user_size(x, ptr, size, retval) \
> @@ -141,20 +133,6 @@ __pu_failed: \
> __pu_err; \
> })
>
> -#define __put_user_nosleep(x, ptr, size) \
> -({ \
> - long __pu_err; \
> - __typeof__(*(ptr)) __user *__pu_addr = (ptr); \
> - __typeof__(*(ptr)) __pu_val = (x); \
> - __typeof__(size) __pu_size = (size); \
> - \
> - __chk_user_ptr(__pu_addr); \
> - __put_user_size(__pu_val, __pu_addr, __pu_size, __pu_err); \
> - \
> - __pu_err; \
> -})
> -
> -
> /*
> * We don't tell gcc that we are accessing memory, but this is OK
> * because we do not write to any memory gcc knows about, so there
> @@ -320,21 +298,6 @@ do { \
> __gu_err; \
> })
>
> -#define __get_user_nosleep(x, ptr, size) \
> -({ \
> - long __gu_err; \
> - __long_type(*(ptr)) __gu_val; \
> - __typeof__(*(ptr)) __user *__gu_addr = (ptr); \
> - __typeof__(size) __gu_size = (size); \
> - \
> - __chk_user_ptr(__gu_addr); \
> - __get_user_size(__gu_val, __gu_addr, __gu_size, __gu_err); \
> - (x) = (__force __typeof__(*(ptr)))__gu_val; \
> - \
> - __gu_err; \
> -})
> -
> -
> /* more complex routines */
>
> extern unsigned long __copy_tofrom_user(void __user *to,
> diff --git a/arch/powerpc/kernel/align.c b/arch/powerpc/kernel/align.c
> index c7797eb958c7..83b199026a1e 100644
> --- a/arch/powerpc/kernel/align.c
> +++ b/arch/powerpc/kernel/align.c
> @@ -174,18 +174,18 @@ static int emulate_spe(struct pt_regs *regs, unsigned int reg,
>
> switch (nb) {
> case 8:
> - ret |= __get_user_inatomic(temp.v[0], p++);
> - ret |= __get_user_inatomic(temp.v[1], p++);
> - ret |= __get_user_inatomic(temp.v[2], p++);
> - ret |= __get_user_inatomic(temp.v[3], p++);
> + ret |= __get_user(temp.v[0], p++);
> + ret |= __get_user(temp.v[1], p++);
> + ret |= __get_user(temp.v[2], p++);
> + ret |= __get_user(temp.v[3], p++);
> fallthrough;
> case 4:
> - ret |= __get_user_inatomic(temp.v[4], p++);
> - ret |= __get_user_inatomic(temp.v[5], p++);
> + ret |= __get_user(temp.v[4], p++);
> + ret |= __get_user(temp.v[5], p++);
> fallthrough;
> case 2:
> - ret |= __get_user_inatomic(temp.v[6], p++);
> - ret |= __get_user_inatomic(temp.v[7], p++);
> + ret |= __get_user(temp.v[6], p++);
> + ret |= __get_user(temp.v[7], p++);
> if (unlikely(ret))
> return -EFAULT;
> }
> @@ -259,18 +259,18 @@ static int emulate_spe(struct pt_regs *regs, unsigned int reg,
> p = addr;
> switch (nb) {
> case 8:
> - ret |= __put_user_inatomic(data.v[0], p++);
> - ret |= __put_user_inatomic(data.v[1], p++);
> - ret |= __put_user_inatomic(data.v[2], p++);
> - ret |= __put_user_inatomic(data.v[3], p++);
> + ret |= __put_user(data.v[0], p++);
> + ret |= __put_user(data.v[1], p++);
> + ret |= __put_user(data.v[2], p++);
> + ret |= __put_user(data.v[3], p++);
> fallthrough;
> case 4:
> - ret |= __put_user_inatomic(data.v[4], p++);
> - ret |= __put_user_inatomic(data.v[5], p++);
> + ret |= __put_user(data.v[4], p++);
> + ret |= __put_user(data.v[5], p++);
> fallthrough;
> case 2:
> - ret |= __put_user_inatomic(data.v[6], p++);
> - ret |= __put_user_inatomic(data.v[7], p++);
> + ret |= __put_user(data.v[6], p++);
> + ret |= __put_user(data.v[7], p++);
> }
> if (unlikely(ret))
> return -EFAULT;
> diff --git a/arch/powerpc/kernel/hw_breakpoint_constraints.c b/arch/powerpc/kernel/hw_breakpoint_constraints.c
> index 867ee4aa026a..675d1f66ab72 100644
> --- a/arch/powerpc/kernel/hw_breakpoint_constraints.c
> +++ b/arch/powerpc/kernel/hw_breakpoint_constraints.c
> @@ -141,7 +141,7 @@ void wp_get_instr_detail(struct pt_regs *regs, struct ppc_inst *instr,
> {
> struct instruction_op op;
>
> - if (__get_user_instr_inatomic(*instr, (void __user *)regs->nip))
> + if (__get_user_instr(*instr, (void __user *)regs->nip))
> return;
>
> analyse_instr(&op, regs, *instr);
> diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c
> index 1583fd1c6010..1fa36bd08efe 100644
> --- a/arch/powerpc/kernel/traps.c
> +++ b/arch/powerpc/kernel/traps.c
> @@ -864,7 +864,7 @@ static void p9_hmi_special_emu(struct pt_regs *regs)
> unsigned long ea, msr, msr_mask;
> bool swap;
>
> - if (__get_user_inatomic(instr, (unsigned int __user *)regs->nip))
> + if (__get_user(instr, (unsigned int __user *)regs->nip))
> return;
>
> /*
> --
> 2.25.0