linux-kernel - Re: [PATCH v2] irqchip/gic-v3-its: Reset each ITS's BASERn register before probe

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Message-ID: <a19d7f44abfd38eb429e33d4886518e3@kernel.org>
Date:   Sat, 22 Jan 2022 17:31:02 +0000
From:   Marc Zyngier <maz@...nel.org>
To:     linux-kernel@...r.kernel.org
Cc:     Thomas Gleixner <tglx@...utronix.de>, kernel-team@...roid.com,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Jay Chen <jkchen@...ux.alibaba.com>
Subject: Re: [PATCH v2] irqchip/gic-v3-its: Reset each ITS's BASERn register
 before probe

On 2022-01-22 16:37, Marc Zyngier wrote:
> A recent bug report outlined that the way GICv4.1 is handled across
> kexec is pretty bad. We can end-up in a situation where ITSs share
> memory (this is the case when SVPET==1) and reprogram the base
> registers, creating a situation where ITSs that are part of a given
> affinity group see different pointers. Which is illegal. Boo.
> 
> In order to restore some sanity, reset the BASERn registers to 0
> *before* probing any ITS. Although this isn't optimised at all,
> this is only a once-per-boot cost, which shouldn't show up on
> anyone's radar.
> 
> Cc: Lorenzo Pieralisi <lorenzo.pieralisi@....com>
> Cc: Jay Chen <jkchen@...ux.alibaba.com>
> Signed-off-by: Marc Zyngier <maz@...nel.org>
> Link: https://lore.kernel.org/r/20211216190315.GA14220@lpieralisi
> ---
> 
> Notes:
>     * From v1: Fail probing if any ITS fails to reset.
> 
>  drivers/irqchip/irq-gic-v3-its.c | 111 +++++++++++++++++++++++++------
>  1 file changed, 92 insertions(+), 19 deletions(-)
> 

[...]

>  static void __init its_acpi_probe(void)
>  {
>  	acpi_table_parse_srat_its();
> +	if (acpi_table_parse_madt(ACPI_MADT_TYPE_GENERIC_TRANSLATOR,
> +				  its_acpi_reset, 0))
> +		return;

Nah. This is obviously broken.

I'll repost something once I have actually tested it on an ACPI box.

         M.
-- 
Jazz is not dead. It just smells funny...