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 <npig...@gmail.com>
>
> Signed-off-by: Rohan McLure <rmcl...@linux.ibm.com>
> Reported-by: Michael Ellerman <m...@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
