linux-kernel - Re: [PATCH v3 2/7] iommu/dma-iommu: Split iommu_dma_map_msi

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Date:   Fri, 3 May 2019 16:03:55 +0200
From:   Joerg Roedel <joro@...tes.org>
To:     Julien Grall <julien.grall@....com>
Cc:     linux-kernel@...r.kernel.org, iommu@...ts.linux-foundation.org,
        logang@...tatee.com, douliyangs@...il.com,
        miquel.raynal@...tlin.com, marc.zyngier@....com,
        jason@...edaemon.net, tglx@...utronix.de, robin.murphy@....com,
        bigeasy@...utronix.de, linux-rt-users@...r.kernel.org,
        Eric Auguer <eric.auger@...hat.com>
Subject: Re: [PATCH v3 2/7] iommu/dma-iommu: Split iommu_dma_map_msi_msg() in
 two parts

On Wed, May 01, 2019 at 02:58:19PM +0100, Julien Grall wrote:
> On RT, iommu_dma_map_msi_msg() may be called from non-preemptible
> context. This will lead to a splat with CONFIG_DEBUG_ATOMIC_SLEEP as
> the function is using spin_lock (they can sleep on RT).
> 
> iommu_dma_map_msi_msg() is used to map the MSI page in the IOMMU PT
> and update the MSI message with the IOVA.
> 
> Only the part to lookup for the MSI page requires to be called in
> preemptible context. As the MSI page cannot change over the lifecycle
> of the MSI interrupt, the lookup can be cached and re-used later on.
> 
> iomma_dma_map_msi_msg() is now split in two functions:
>     - iommu_dma_prepare_msi(): This function will prepare the mapping
>     in the IOMMU and store the cookie in the structure msi_desc. This
>     function should be called in preemptible context.
>     - iommu_dma_compose_msi_msg(): This function will update the MSI
>     message with the IOVA when the device is behind an IOMMU.
> 
> Signed-off-by: Julien Grall <julien.grall@....com>
> Reviewed-by: Robin Murphy <robin.murphy@....com>
> Reviewed-by: Eric Auguer <eric.auger@...hat.com>

Acked-by: Joerg Roedel <jroedel@...e.de>