Messages in this thread | | | Date | Wed, 4 Jan 2023 21:19:12 +0530 | Subject | Re: Query about IPI as NMI (pseudo-NMI) support patches | From | Mukesh Ojha <> |
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Hi Marc,
Thanks for your patience in replying queries
On 1/3/2023 11:15 PM, Marc Zyngier wrote: > On Tue, 03 Jan 2023 16:45:04 +0000, > Mukesh Ojha <quic_mojha@quicinc.com> wrote: >> >> Hi, >> >> Thanks for your reply. >> >> On 1/2/2023 10:41 PM, Marc Zyngier wrote: >>> Hi Mukesh, >>> >>> On Mon, 02 Jan 2023 16:44:59 +0000, >>> Mukesh Ojha <quic_mojha@quicinc.com> wrote: >>>> >>>> Hi Marc, >>>> >>>> I was looking similar support mentioned in below patch series. >>>> >>>> https://lore.kernel.org/lkml/CAFA6WYO0+LQ=mB1spCstt0cNZ0G+sZu_+Wrv6BKSeXqF5SRq4A@mail.gmail.com/#t >>>> >>>> Wanted to check if there is chance of these patches to land in >>>> mainline ? >>> >>> I certainly have no intention to merge it as is, specially as there is >>> no good usage model for it other than "but think of debug!". >>> >>> We have exactly *one* SGI left. If we are going to lose it over such a >>> feature, I'd want a description of how we are going to share it >>> between potential users, and how we claw some currently used SGIs >>> back. >> >> >> But, looks like patch will fail if SGI is not available. >> >> https://lore.kernel.org/lkml/1604317487-14543-4-git-send-email-sumit.garg@linaro.org/ >> >> >> >> set_smp_ipi_range(base_sgi, 8); >> >> + if (n > nr_ipi) >> + set_smp_dynamic_ipi(ipi_base + nr_ipi); >> + >> >> So, static SGI allocation still has higher priority than dynamic >> one. Would you be accepting if we keep it under some >> CONFIG_ARM64_IPI_NMI_DEBUG ? > > But why should this thing have priority over other potential features? > As I said above, there are two requirements: > > - being able to share a single NMI SGI amongst multiple users > > - being able to free existing SGIs in case we absolutely need an SGI > for some other purposes > > In both cases, this is about making the SGI space scale *beyond* the 8 > possible interrupts that we have. This needs to be solved to get > something like this in.
Agree, we have shortage of SGI's, Will try to think if we can fix this.
However, I think IPI_CPU_STOP is something which can be used as an NMI, As this will be used only(once) during panic()->send_smp_stop().
Can we do some special handling for IPI_CPU_STOP similar to pmu interrupts like request it as NMI and fallback to normal irq if not supported/on error ?
> > And I don't think hiding this behind an obscure "debug" configuration > option that will get abused with out of tree stuff is a good move. > Quite the opposite. >
Thanks, Make sense.
> Thanks, > > M. >
-Mukesh
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