linux-kernel - Re: [PATCH v3 09/10] iommu/dart: Exclude MSI doorbell from PCIe device IOVA range

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Message-Id: <479322ce-b0e4-40e4-831e-387415b4e310@www.fastmail.com>
Date:   Tue, 14 Sep 2021 15:54:07 +0200
From:   "Sven Peter" <sven@...npeter.dev>
To:     "Marc Zyngier" <maz@...nel.org>, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org
Cc:     "Bjorn Helgaas" <bhelgaas@...gle.com>,
        "Rob Herring" <robh+dt@...nel.org>,
        "Lorenzo Pieralisi" <lorenzo.pieralisi@....com>,
        Krzysztof Wilczyński <kw@...ux.com>,
        "Alyssa Rosenzweig" <alyssa@...enzweig.io>,
        "Stan Skowronek" <stan@...ellium.com>,
        "Mark Kettenis" <kettenis@...nbsd.org>,
        "Hector Martin" <marcan@...can.st>,
        "Robin Murphy" <Robin.Murphy@....com>, kernel-team@...roid.com
Subject: Re: [PATCH v3 09/10] iommu/dart: Exclude MSI doorbell from PCIe device IOVA range



On Mon, Sep 13, 2021, at 20:25, Marc Zyngier wrote:
> The MSI doorbell on Apple HW can be any address in the low 4GB
> range. However, the MSI write is matched by the PCIe block before
> hitting the iommu. It must thus be excluded from the IOVA range
> that is assigned to any PCIe device.
> 
> Signed-off-by: Marc Zyngier <maz@...nel.org>

It's not pretty but I'm not aware of any better solution and this should
work as long as these two are always paired. With the small nit below
addressed:

Reviewed-by: Sven Peter <sven@...npeter.dev>

> ---
>  drivers/iommu/apple-dart.c          | 25 +++++++++++++++++++++++++
>  drivers/pci/controller/Kconfig      |  5 +++++
>  drivers/pci/controller/pcie-apple.c |  4 +++-
>  3 files changed, 33 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/iommu/apple-dart.c b/drivers/iommu/apple-dart.c
> index 559db9259e65..d1456663688e 100644
> --- a/drivers/iommu/apple-dart.c
> +++ b/drivers/iommu/apple-dart.c
> @@ -721,6 +721,29 @@ static int apple_dart_def_domain_type(struct device *dev)
>  	return 0;
>  }
>  
> +#define DOORBELL_ADDR	(CONFIG_PCIE_APPLE_MSI_DOORBELL_ADDR & PAGE_MASK)
> +
> +static void apple_dart_get_resv_regions(struct device *dev,
> +					struct list_head *head)
> +{
> +#ifdef CONFIG_PCIE_APPLE

I think using IS_ENABLED would be better here in case the pcie driver is built as
a module which would then only define CONFIG_PCIE_APPLE_MODULE AIUI.


Thanks,


Sven