[PATCH 05/12] powerpc: Mark [h]ssr_valid accesses in check_return_regs_valid

[Nicholas Piggin]

On Mon May 8, 2023 at 12:01 PM AEST, Rohan McLure wrote:
> Checks to see if the [H]SRR registers have been clobbered by (soft)
> NMI interrupts imply the possibility for a data race on the
> [h]srr_valid entries in the PACA. Annotate accesses to these fields with
> READ_ONCE, removing the need for the barrier.
>
> The diagnostic can use plain-access reads and writes, but annotate with
> data_race.

Reviewed-by: Nicholas Piggin <npiggin at gmail.com>

>
> Signed-off-by: Rohan McLure <rmclure at linux.ibm.com>
> Reported-by: Michael Ellerman <mpe at ellerman.id.au>
> ---
>  arch/powerpc/include/asm/ptrace.h |  4 ++--
>  arch/powerpc/kernel/interrupt.c   | 14 ++++++--------
>  2 files changed, 8 insertions(+), 10 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/ptrace.h b/arch/powerpc/include/asm/ptrace.h
> index 0eb90a013346..9db8b16567e2 100644
> --- a/arch/powerpc/include/asm/ptrace.h
> +++ b/arch/powerpc/include/asm/ptrace.h
> @@ -180,8 +180,8 @@ void do_syscall_trace_leave(struct pt_regs *regs);
>  static inline void set_return_regs_changed(void)
>  {
>  #ifdef CONFIG_PPC_BOOK3S_64
> -	local_paca->hsrr_valid = 0;
> -	local_paca->srr_valid = 0;
> +	WRITE_ONCE(local_paca->hsrr_valid, 0);
> +	WRITE_ONCE(local_paca->srr_valid, 0);
>  #endif
>  }
>  
> diff --git a/arch/powerpc/kernel/interrupt.c b/arch/powerpc/kernel/interrupt.c
> index e34c72285b4e..1f033f11b871 100644
> --- a/arch/powerpc/kernel/interrupt.c
> +++ b/arch/powerpc/kernel/interrupt.c
> @@ -125,7 +125,7 @@ static notrace void check_return_regs_valid(struct pt_regs *regs)
>  	case 0x1600:
>  	case 0x1800:
>  		validp = &local_paca->hsrr_valid;
> -		if (!*validp)
> +		if (!READ_ONCE(*validp))
>  			return;
>  
>  		srr0 = mfspr(SPRN_HSRR0);
> @@ -135,7 +135,7 @@ static notrace void check_return_regs_valid(struct pt_regs *regs)
>  		break;
>  	default:
>  		validp = &local_paca->srr_valid;
> -		if (!*validp)
> +		if (!READ_ONCE(*validp))
>  			return;
>  
>  		srr0 = mfspr(SPRN_SRR0);
> @@ -161,19 +161,17 @@ static notrace void check_return_regs_valid(struct pt_regs *regs)
>  	 * such things will get caught most of the time, statistically
>  	 * enough to be able to get a warning out.
>  	 */
> -	barrier();
> -
> -	if (!*validp)
> +	if (!READ_ONCE(*validp))
>  		return;
>  
> -	if (!warned) {
> -		warned = true;
> +	if (!data_race(warned)) {
> +		data_race(warned = true);
>  		printk("%sSRR0 was: %lx should be: %lx\n", h, srr0, regs->nip);
>  		printk("%sSRR1 was: %lx should be: %lx\n", h, srr1, regs->msr);
>  		show_regs(regs);
>  	}
>  
> -	*validp = 0; /* fixup */
> +	WRITE_ONCE(*validp, 0); /* fixup */
>  #endif
>  }
>  
> -- 
> 2.37.2