linux-kernel - Re: [PATCH v1 01/14] iommu: Add iommu_get_unmanaged

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Message-ID: <ZBN1nbjHzu1BJdOO@Asurada-Nvidia>
Date:   Thu, 16 Mar 2023 13:01:33 -0700
From:   Nicolin Chen <nicolinc@...dia.com>
To:     Robin Murphy <robin.murphy@....com>
CC:     Jason Gunthorpe <jgg@...dia.com>,
        Eric Auger <eric.auger@...hat.com>, <will@...nel.org>,
        <kevin.tian@...el.com>, <baolu.lu@...ux.intel.com>,
        <joro@...tes.org>, <shameerali.kolothum.thodi@...wei.com>,
        <jean-philippe@...aro.org>, <linux-arm-kernel@...ts.infradead.org>,
        <iommu@...ts.linux.dev>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1 01/14] iommu: Add iommu_get_unmanaged_domain helper

On Thu, Mar 16, 2023 at 06:42:07PM +0000, Robin Murphy wrote:
> External email: Use caution opening links or attachments
> 
> 
> On 16/03/2023 1:21 am, Nicolin Chen wrote:
> > Hi Robin,
> > 
> > How do you think about Jason's proposal below? I'd like to see
> > us come to an agreement on an acceptable solution...
> 
> I think it's so thoroughly broken that I suspect Cunningham's law might
> be at play, but fine, you win :) Hopefully it's sufficiently obvious how
> the other pieces would fit around the patch below. FWIW I'd still prefer
> a generic domain->s2_domain pointer rather than any op at all, but I'm
> happy enough with this compromise.

Oh, I appreciate that! Looks like we can move on with a v2 :)

I will include this patch replacing mine in the next version.

Thanks!
Nic

> ----->8-----
> Subject: [PATCH] iommu/dma: Support MSIs through nested domains
> 
> Currently, iommu-dma is the only place outside of IOMMUFD and drivers
> which might need to be aware of the stage 2 domain encapsulated within
> a nested domain. This would be in the legacy-VFIO-style case where we're
> using host-managed MSIs with an identity mapping at stage 1, where it is
> the underlying stage 2 domain which owns an MSI cookie and holds the
> corresponding dynamic mappings. Hook up the new op to resolve what we
> need from a nested domain.
> 
> Signed-off-by: Robin Murphy <robin.murphy@....com>
> ---
>  drivers/iommu/dma-iommu.c | 18 ++++++++++++++++--
>  1 file changed, 16 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
> index 99b2646cb5c7..66b0d5fa49f8 100644
> --- a/drivers/iommu/dma-iommu.c
> +++ b/drivers/iommu/dma-iommu.c
> @@ -1642,6 +1642,20 @@ static struct iommu_dma_msi_page *iommu_dma_get_msi_page(struct device *dev,
>        return NULL;
>  }
> 
> +/*
> + * Nested domains may not have an MSI cookie or accept mappings, but they may
> + * be related to a domain which does, so we let them tell us what they need.
> + */
> +static struct iommu_domain *iommu_dma_get_msi_mapping_domain(struct device *dev)
> +{
> +       struct iommu_domain *domain = iommu_get_domain_for_dev(dev);
> +
> +       if (domain && domain->type == IOMMU_DOMAIN_NESTED &&
> +           domain->ops->get_msi_mapping_domain)
> +               domain = domain->ops->get_msi_mapping_domain(domain);
> +       return domain;
> +}
> +
>  /**
>   * iommu_dma_prepare_msi() - Map the MSI page in the IOMMU domain
>   * @desc: MSI descriptor, will store the MSI page
> @@ -1652,7 +1666,7 @@ static struct iommu_dma_msi_page *iommu_dma_get_msi_page(struct device *dev,
>  int iommu_dma_prepare_msi(struct msi_desc *desc, phys_addr_t msi_addr)
>  {
>        struct device *dev = msi_desc_to_dev(desc);
> -       struct iommu_domain *domain = iommu_get_domain_for_dev(dev);
> +       struct iommu_domain *domain = iommu_dma_get_msi_mapping_domain(dev);
>        struct iommu_dma_msi_page *msi_page;
>        static DEFINE_MUTEX(msi_prepare_lock); /* see below */
> 
> @@ -1685,7 +1699,7 @@ int iommu_dma_prepare_msi(struct msi_desc *desc, phys_addr_t msi_addr)
>  void iommu_dma_compose_msi_msg(struct msi_desc *desc, struct msi_msg *msg)
>  {
>        struct device *dev = msi_desc_to_dev(desc);
> -       const struct iommu_domain *domain = iommu_get_domain_for_dev(dev);
> +       const struct iommu_domain *domain = iommu_dma_get_msi_mapping_domain(dev);
>        const struct iommu_dma_msi_page *msi_page;
> 
>        msi_page = msi_desc_get_iommu_cookie(desc);
> --
> 2.39.2.101.g768bb238c484.dirty
>