linux-kernel - Re: Query about IPI as NMI (pseudo-NMI) support patches

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Message-ID: <a20a9592-05e7-c529-5ab1-d7d52fffa59a@quicinc.com>
Date:   Tue, 3 Jan 2023 22:15:04 +0530
From:   Mukesh Ojha <quic_mojha@...cinc.com>
To:     Marc Zyngier <maz@...nel.org>
CC:     lkml <linux-kernel@...r.kernel.org>
Subject: Re: Query about IPI as NMI (pseudo-NMI) support patches

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@...cinc.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 ?

-Mukesh
> 
> Until then, this is a proof of concept, and not much else.
> 
> Thanks,
> 
> 	M.
>