From: "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>
To: Michael Ellerman <mpe@ellerman.id.au>
Cc: Anju T Sudhakar <anju@linux.vnet.ibm.com>,
linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
ananth@in.ibm.com, mahesh@linux.vnet.ibm.com, paulus@samba.org,
mhiramat@kernel.org, srikar@linux.vnet.ibm.com
Subject: Re: [PATCH V3 3/4] arch/powerpc: Implement Optprobes
Date: Sat, 4 Feb 2017 01:09:49 +0530 [thread overview]
Message-ID: <20170203193949.GD4090@naverao1-tp.localdomain> (raw)
In-Reply-To: <87a8a6dvwo.fsf@concordia.ellerman.id.au>
Hi Michael,
Thanks for the review! I'll defer to Anju on most of the aspects, but...
On 2017/02/01 09:53PM, Michael Ellerman wrote:
> Anju T Sudhakar <anju@linux.vnet.ibm.com> writes:
>
> > +static void optimized_callback(struct optimized_kprobe *op,
> > + struct pt_regs *regs)
> > +{
> > + struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
> > + unsigned long flags;
> > +
> > + /* This is possible if op is under delayed unoptimizing */
> > + if (kprobe_disabled(&op->kp))
> > + return;
> > +
> > + local_irq_save(flags);
>
> What is that protecting against? Because on powerpc it doesn't actually
> disable interrupts, it just masks some of them, the perf interrupt for
> example can still run.
That's an excellent catch, as always! :)
This is meant to prevent us from missing kprobe hits while processing
interrupts that arrive when this optprobe is being handled. And you are
totally right -- we would miss kprobe hits during PMI handling with the
current approach. We need a hard_irq_disable() there.
> > + /*
> > + * Optprobe template:
> > + * This template gets copied into one of the slots in optinsn_slot
> > + * and gets fixed up with real optprobe structures et al.
> > + */
> > + .global optprobe_template_entry
> > +optprobe_template_entry:
> > + /* Create an in-memory pt_regs */
> > + stdu r1,-INT_FRAME_SIZE(r1)
> > + SAVE_GPR(0,r1)
> > + /* Save the previous SP into stack */
> > + addi r0,r1,INT_FRAME_SIZE
> > + std r0,GPR1(r1)
> > + SAVE_10GPRS(2,r1)
> > + SAVE_10GPRS(12,r1)
> > + SAVE_10GPRS(22,r1)
> > + /* Save SPRS */
> > + mfmsr r5
> > + std r5,_MSR(r1)
> > + li r5,0x700
> > + std r5,_TRAP(r1)
> > + li r5,0
> > + std r5,ORIG_GPR3(r1)
> > + std r5,RESULT(r1)
> > + mfctr r5
> > + std r5,_CTR(r1)
> > + mflr r5
> > + std r5,_LINK(r1)
> > + mfspr r5,SPRN_XER
> > + std r5,_XER(r1)
> > + mfcr r5
> > + std r5,_CCR(r1)
> > + lbz r5,PACASOFTIRQEN(r13)
> > + std r5,SOFTE(r1)
> > + mfdar r5
> > + std r5,_DAR(r1)
> > + mfdsisr r5
> > + std r5,_DSISR(r1)
>
> So this is what made me originally reply to this patch. This
> save/restore sequence.
>
> I'm not clear on why this is what we need to save/restore.
>
> Aren't we essentially just interposing a function call? If so do we need
> to save/restore all of these? eg. MSR/DAR/DSISR. Non-volatile GPRs? And
> why are we pretending there was a 0x700 trap?
>
> Is it because we're going to end up emulating the instruction and so we
> need everything in pt_regs ?
Yes, that and also for the kprobe pre_handler() which takes pt_regs.
Regards,
- Naveen
next prev parent reply other threads:[~2017-02-03 19:40 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-12-19 13:18 [PATCH V3 0/4] OPTPROBES for powerpc Anju T Sudhakar
2016-12-19 13:18 ` [PATCH V3 3/4] arch/powerpc: Implement Optprobes Anju T Sudhakar
2016-12-25 2:54 ` Masami Hiramatsu
2017-01-04 10:25 ` Naveen N. Rao
2017-01-30 20:43 ` Michael Ellerman
2017-01-31 7:55 ` Naveen N. Rao
2017-01-31 7:59 ` [PATCH] powerpc: kprobes: fixes for kprobe_lookup_name on BE Naveen N. Rao
2017-02-01 10:53 ` [PATCH V3 3/4] arch/powerpc: Implement Optprobes Michael Ellerman
2017-02-03 19:39 ` Naveen N. Rao [this message]
2017-02-07 1:05 ` Masami Hiramatsu
2017-02-07 7:51 ` Naveen N. Rao
2017-02-08 5:37 ` Anju T Sudhakar
2016-12-19 13:18 ` [PATCH V3 4/4] arch/powerpc: Optimize kprobe in kretprobe_trampoline Anju T Sudhakar
2016-12-19 13:18 ` [PATCH V3 1/4] powerpc: asm/ppc-opcode.h: introduce __PPC_SH64() Anju T Sudhakar
2016-12-19 13:18 ` [PATCH V3 2/4] powerpc: add helper to check if offset is within rel branch range Anju T Sudhakar
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