linux-kernel - Re: [SPLAT 2/3] irqchip/gic-v3-its: Sleeping spinlocks down gic_reserve

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Date:   Wed, 11 Aug 2021 14:28:21 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Marc Zyngier <maz@...nel.org>,
        Valentin Schneider <valentin.schneider@....com>
Cc:     linux-kernel@...r.kernel.org, linux-rt-users@...r.kernel.org,
        Will Deacon <will@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Ard Biesheuvel <ardb@...nel.org>
Subject: Re: [SPLAT 2/3] irqchip/gic-v3-its: Sleeping spinlocks down
 gic_reserve_range()

On Wed, Aug 11 2021 at 09:50, Marc Zyngier wrote:
> On Tue, 10 Aug 2021 14:41:26 +0100,
> Valentin Schneider <valentin.schneider@....com> wrote:
> The issue is that although the redistributor tables have been
> allocated ahead of time (outside of any cpuhp callback), they cannot
> be programmed into the RDs until the corresponding CPUs have been
> brought up (the registers may not be accessible).
>
> For the same reason, we don't know whether we can free them (because
> there is already a table programmed there) or have to reserve them
> with an efi_mem_reserve_persistent() call. efi_mem_reserve_iomem()
> uses GFP_ATOMIC for its allocation, but this is not sufficient for RT
> anymore.
>
> We could postpone the reservation of the memory to a later point (it
> is only useful for kexec), but it isn't clear where that point is. The
> CPU is not quite up yet, and we can't easily IPI the boot CPU to do
> the reserve call.

Right, but don't you know about the need for reservation _before_
bringing the CPU up?

Thanks,

        tglx