Messages in this thread | | | Date | Sat, 4 Feb 2017 01:09:49 +0530 | From | "Naveen N. Rao" <> | Subject | Re: [PATCH V3 3/4] arch/powerpc: Implement Optprobes |
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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
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