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From: Jordan Niethe <jniethe5@gmail.com>
Date: Mon, 23 Mar 2020 20:35:50 +1100
Message-ID: <CACzsE9poG75tQoT05oBVJP4zs0ZwB2cB+-PNdx-3xrDuEJjyLQ@mail.gmail.com>
Subject: Re: [PATCH v4 13/16] powerpc: Support prefixed instructions in
 alignment handler
To: Nicholas Piggin <npiggin@gmail.com>
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Cc: Alistair Popple <alistair@popple.id.au>,
 Balamuruhan S <bala24@linux.ibm.com>, linuxppc-dev@lists.ozlabs.org,
 Daniel Axtens <dja@axtens.net>
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On Mon, Mar 23, 2020 at 6:09 PM Nicholas Piggin <npiggin@gmail.com> wrote:
>
> 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 <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: 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.
Good point.
>
> Thanks,
> Nick