Subject: Re: [PATCH v4 13/16] powerpc: Support prefixed instructions in alignment handler

From: Nicholas Piggin <[email-masked]>
Date: Mon, 23 Mar 2020 17:05:42 +1000

Jordan Niethe's on March 20, 2020 3:18 pm:
> Alignment interrupts can be caused by prefixed instructions accessing
> memory. Prefixed instructions are not permitted to cross 64-byte
> boundaries. If they do the alignment interrupt is invoked with SRR1
> BOUNDARY bit set.  If this occurs send a SIGBUS to the offending process
> if in user mode.  If in kernel mode call bad_page_fault().
> 
> Signed-off-by: Jordan Niethe <[email-masked]>
> ---
> v2: - Move __get_user_instr() and __get_user_instr_inatomic() to this
> commit (previously in "powerpc sstep: Prepare to support prefixed
> instructions").
>     - Rename sufx to suffix
>     - Use a macro for calculating instruction length
> v3: Move __get_user_{instr(), instr_inatomic()} up with the other
> get_user definitions and remove nested if.
> v4: Just do the things for alignment_exception(). Other changes handled
> elsewhere.
> ---
>  arch/powerpc/kernel/traps.c | 21 ++++++++++++++++++++-
>  1 file changed, 20 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c
> index a4764b039749..cd8b3043c268 100644
> --- a/arch/powerpc/kernel/traps.c
> +++ b/arch/powerpc/kernel/traps.c
> @@ -583,6 +583,10 @@ static inline int check_io_access(struct pt_regs *regs)
>  #define REASON_ILLEGAL		(ESR_PIL | ESR_PUO)
>  #define REASON_PRIVILEGED	ESR_PPR
>  #define REASON_TRAP		ESR_PTR
> +#define REASON_PREFIXED		0
> +#define REASON_BOUNDARY		0
> +
> +#define inst_length(reason)	4
>  
>  /* single-step stuff */
>  #define single_stepping(regs)	(current->thread.debug.dbcr0 & DBCR0_IC)
> @@ -597,6 +601,10 @@ static inline int check_io_access(struct pt_regs *regs)
>  #define REASON_ILLEGAL		SRR1_PROGILL
>  #define REASON_PRIVILEGED	SRR1_PROGPRIV
>  #define REASON_TRAP		SRR1_PROGTRAP
> +#define REASON_PREFIXED		SRR1_PREFIXED
> +#define REASON_BOUNDARY		SRR1_BOUNDARY
> +
> +#define inst_length(reason)	(((reason) & REASON_PREFIXED) ? 8 : 4)

Looks good. If you define REASON_BOUNDARY 0, then this will constant
fold away so no need to define it twice.

Thanks,
Nick