Re: [PATCH v7 26/28] powerpc: Support prefixed instructions in alignment handler

[Alistair Popple <alistair@popple.id.au>]

Reviewed-by: Alistair Popple <alistair@popple.id.au>

On Friday, 1 May 2020 1:42:18 PM AEST Jordan Niethe wrote:
> If a prefixed instruction results in an alignment exception, the
> SRR1_PREFIXED bit is set. The handler attempts to emulate the
> responsible instruction and then increment the NIP past it. Use
> SRR1_PREFIXED to determine by how much the NIP should be incremented.
> 
> 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 <jniethe5@gmail.com>
> ---
> 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: Rolled into "Add prefixed instructions to instruction data type"
> v5: Only one definition of inst_length()
> ---
>  arch/powerpc/kernel/traps.c | 19 ++++++++++++++++++-
>  1 file changed, 18 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c
> index 493a3fa0ac1a..105242cc2f28 100644
> --- a/arch/powerpc/kernel/traps.c
> +++ b/arch/powerpc/kernel/traps.c
> @@ -583,6 +583,8 @@ 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
> 
>  /* single-step stuff */
>  #define single_stepping(regs)	(current->thread.debug.dbcr0 & DBCR0_IC)
> @@ -597,12 +599,16 @@ 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 single_stepping(regs)	((regs)->msr & MSR_SE)
>  #define clear_single_step(regs)	((regs)->msr &= ~MSR_SE)
>  #define clear_br_trace(regs)	((regs)->msr &= ~MSR_BE)
>  #endif
> 
> +#define inst_length(reason)	(((reason) & REASON_PREFIXED) ? 8 : 4)
> +
>  #if defined(CONFIG_E500)
>  int machine_check_e500mc(struct pt_regs *regs)
>  {
> @@ -1593,11 +1599,20 @@ void alignment_exception(struct pt_regs *regs)
>  {
>  	enum ctx_state prev_state = exception_enter();
>  	int sig, code, fixed = 0;
> +	unsigned long  reason;
> 
>  	/* We restore the interrupt state now */
>  	if (!arch_irq_disabled_regs(regs))
>  		local_irq_enable();
> 
> +	reason = get_reason(regs);
> +
> +	if (reason & REASON_BOUNDARY) {
> +		sig = SIGBUS;
> +		code = BUS_ADRALN;
> +		goto bad;
> +	}
> +
>  	if (tm_abort_check(regs, TM_CAUSE_ALIGNMENT | TM_CAUSE_PERSISTENT))
>  		goto bail;
> 
> @@ -1606,7 +1621,8 @@ void alignment_exception(struct pt_regs *regs)
>  		fixed = fix_alignment(regs);
> 
>  	if (fixed == 1) {
> -		regs->nip += 4;	/* skip over emulated instruction */
> +		/* skip over emulated instruction */
> +		regs->nip += inst_length(reason);
>  		emulate_single_step(regs);
>  		goto bail;
>  	}
> @@ -1619,6 +1635,7 @@ void alignment_exception(struct pt_regs *regs)
>  		sig = SIGBUS;
>  		code = BUS_ADRALN;
>  	}
> +bad:
>  	if (user_mode(regs))
>  		_exception(sig, regs, code, regs->dar);
>  	else