Messages in this thread | ![/](/images/icornerl.gif) | | Date | Thu, 19 Jan 2023 22:12:12 +0530 | Subject | Re: Query about IPI as NMI (pseudo-NMI) support patches | From | Mukesh Ojha <> |
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Hi Marc,
On 1/4/2023 9:19 PM, Mukesh Ojha wrote: > 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 ?
Can we do this ?
-Mukesh > > >> >> 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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