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From: Thomas Gleixner <tglx@linutronix.de>
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To: Troy Mitchell <troy.mitchell@linux.dev>, Paul Walmsley <pjw@kernel.org>,
 Samuel Holland <samuel.holland@sifive.com>, Palmer Dabbelt
 <palmer@dabbelt.com>, Albert Ou <aou@eecs.berkeley.edu>, Alexandre Ghiti
 <alex@ghiti.fr>
Cc: linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org, Troy
 Mitchell <troy.mitchell@linux.dev>
Subject: Re: [PATCH v2] riscv/plic: assign context ID based on hartid
In-Reply-To: <20251027-fix-plic-amp-v2-1-f077b9439112@linux.dev>
References: <20251027-fix-plic-amp-v2-1-f077b9439112@linux.dev>
Date: Thu, 13 Nov 2025 14:47:33 +0100
Message-ID: <87bjl6cadm.ffs@tglx>
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On Mon, Oct 27 2025 at 15:03, Troy Mitchell wrote:
> The PLIC driver for OF-based platforms currently assigns 'context_id = i'
> within the context loop. This implies an assumption that all harts are
> numbered contiguously starting from 0.
>
> In Asymmetric Multi-Processing (AMP) systems, where Linux might boot on
> a non-zero hart ID (e.g., hart4), while other harts (e.g., hart0) are
> running a different OS, this assumption is violated. This can lead to
>  different system inadvertently sharing the same
> PLIC enable_base register. Consequently, this causes configuration
> conflicts and incorrect interrupt handling.
>
> Assign the PLIC context ID based on the actual hart ID provided by the
> OF node. This ensures that each hart context maps to a unique enable
> region within the PLIC, thereby resolving conflicts in AMP setups. This
> change preserves the correct behavior on Symmetric Multi-Processing (SMP)
> and Uniprocessor (UP) systems.

Can the RISCV people please have a look at this?

Thanks,

        tglx