Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Fri, 5 Mar 2021 11:45:50 +0100
From:   Jean-Philippe Brucker <jean-philippe@linaro.org>
To:     Eric Auger <eric.auger@redhat.com>
Cc:     eric.auger.pro@gmail.com, iommu@lists.linux-foundation.org,
        linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
        kvmarm@lists.cs.columbia.edu, will@kernel.org, maz@kernel.org,
        robin.murphy@arm.com, joro@8bytes.org, alex.williamson@redhat.com,
        tn@semihalf.com, zhukeqian1@huawei.com,
        jacob.jun.pan@linux.intel.com, yi.l.liu@intel.com,
        wangxingang5@huawei.com, jiangkunkun@huawei.com,
        zhangfei.gao@linaro.org, zhangfei.gao@gmail.com,
        vivek.gautam@arm.com, shameerali.kolothum.thodi@huawei.com,
        yuzenghui@huawei.com, nicoleotsuka@gmail.com,
        lushenming@huawei.com, vsethi@nvidia.com
Subject: Re: [PATCH v12 03/13] vfio: VFIO_IOMMU_SET_MSI_BINDING
Message-ID: <YEIL3qmcRfhUoRGt@myrica>
References: <20210223210625.604517-1-eric.auger@redhat.com>
 <20210223210625.604517-4-eric.auger@redhat.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20210223210625.604517-4-eric.auger@redhat.com>
Precedence: bulk

Hi,

On Tue, Feb 23, 2021 at 10:06:15PM +0100, Eric Auger wrote:
> This patch adds the VFIO_IOMMU_SET_MSI_BINDING ioctl which aim
> to (un)register the guest MSI binding to the host. This latter
> then can use those stage 1 bindings to build a nested stage
> binding targeting the physical MSIs.

Now that RMR is in the IORT spec, could it be used for the nested MSI
problem?  For virtio-iommu tables I was planning to do it like this:

MSI is mapped at stage-2 with an arbitrary IPA->doorbell PA. We report
this IPA to userspace through iommu_groups/X/reserved_regions. No change
there. Then to the guest we report a reserved identity mapping at IPA
(using RMR, an equivalent DT binding, or probed RESV_MEM for
virtio-iommu). The guest creates that mapping at stage-1, and that's it.
Unless I overlooked something we'd only reuse existing infrastructure and
avoid the SET_MSI_BINDING interface.

Thanks,
Jean