Re: [PATCH v4] irqchip/gicv3: Workaround for NVIDIA erratum T241-FABRIC-4

[Marc Zyngier <maz@kernel.org>]

On Sat, 18 Mar 2023 04:58:12 +0000,
Shanker Donthineni <sdonthineni@nvidia.com> wrote:
> 
> The T241 platform suffers from the T241-FABRIC-4 erratum which causes
> unexpected behavior in the GIC when multiple transactions are received
> simultaneously from different sources. This hardware issue impacts
> NVIDIA server platforms that use more than two T241 chips
> interconnected. Each chip has support for 320 {E}SPIs.
> 
> This issue occurs when multiple packets from different GICs are
> incorrectly interleaved at the target chip. The erratum text below
> specifies exactly what can cause multiple transfer packets susceptible
> to interleaving and GIC state corruption. GIC state corruption can
> lead to a range of problems, including kernel panics, and unexpected
> behavior.
> 
> From the erratum text:
>   "In some cases, inter-socket AXI4 Stream packets with multiple
>   transfers, may be interleaved by the fabric when presented to ARM
>   Generic Interrupt Controller. GIC expects all transfers of a packet
>   to be delivered without any interleaving.
> 
>   The following GICv3 commands may result in multiple transfer packets
>   over inter-socket AXI4 Stream interface:
>    - Register reads from GICD_I* and GICD_N*
>    - Register writes to 64-bit GICD registers other than GICD_IROUTERn*
>    - ITS command MOVALL
> 
>   Multiple commands in GICv4+ utilize multiple transfer packets,
>   including VMOVP, VMOVI, VMAPP, and 64-bit register accesses."
> 
>   This issue impacts system configurations with more than 2 sockets,
>   that require multi-transfer packets to be sent over inter-socket
>   AXI4 Stream interface between GIC instances on different sockets.
>   GICv4 cannot be supported. GICv3 SW model can only be supported
>   with the workaround. Single and Dual socket configurations are not
>   impacted by this issue and support GICv3 and GICv4."
> 
> Link: https://developer.nvidia.com/docs/t241-fabric-4/nvidia-t241-fabric-4-errata.pdf
> 
> Writing to the chip alias region of the GICD_In{E} registers except
> GICD_ICENABLERn has an equivalent effect as writing to the global
> distributor. The SPI interrupt deactivate path is not impacted by
> the erratum.
> 
> To fix this problem, implement a workaround that ensures read accesses
> to the GICD_In{E} registers are directed to the chip that owns the
> SPI, and disables GICv4.x features for KVM. To simplify code changes,
> the gic_configure_irq() function uses the same alias region for both
> read and write operations to GICD_ICFGR.
> 
> Co-developed-by: Vikram Sethi <vsethi@nvidia.com>
> Signed-off-by: Vikram Sethi <vsethi@nvidia.com>
> Signed-off-by: Shanker Donthineni <sdonthineni@nvidia.com>
> ---
> Changes since v2:
>  - Fix the build issue for the 32bit arch
> Changes since v2:
>  - Add accessors for the SOC-ID version & revision
>  - Include "linux/bitfield.h" and "linux/bits.h" in irq-gic-v3.c
> Changes since v1:
>  - Use SMCCC SOC-ID API for detecting the T241 chip
>  - Implement Marc's suggestions
>  - Edit commit text

You seem to have ignored most of my comments on v2[1] apart from the
SOC_ID stuff. I guess I'll wait for v5...

	M.

[1] https://lore.kernel.org/all/871qlqif9v.wl-maz@kernel.org/

-- 
Without deviation from the norm, progress is not possible.

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