linux-kernel - Re: [PATCH v13 02/15] iommu: Introduce bind/unbind_guest

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Date:   Mon, 1 Feb 2021 19:52:44 +0800
From:   Keqian Zhu <zhukeqian1@...wei.com>
To:     Eric Auger <eric.auger@...hat.com>, <eric.auger.pro@...il.com>,
        <iommu@...ts.linux-foundation.org>, <linux-kernel@...r.kernel.org>,
        <kvm@...r.kernel.org>, <kvmarm@...ts.cs.columbia.edu>,
        <will@...nel.org>, <joro@...tes.org>, <maz@...nel.org>,
        <robin.murphy@....com>, <alex.williamson@...hat.com>
CC:     <jean-philippe@...aro.org>, <jacob.jun.pan@...ux.intel.com>,
        <nicoleotsuka@...il.com>, <vivek.gautam@....com>,
        <yi.l.liu@...el.com>, <zhangfei.gao@...aro.org>
Subject: Re: [PATCH v13 02/15] iommu: Introduce bind/unbind_guest_msi

Hi Eric,

On 2020/11/18 19:21, Eric Auger wrote:
> On ARM, MSI are translated by the SMMU. An IOVA is allocated
> for each MSI doorbell. If both the host and the guest are exposed
> with SMMUs, we end up with 2 different IOVAs allocated by each.
> guest allocates an IOVA (gIOVA) to map onto the guest MSI
> doorbell (gDB). The Host allocates another IOVA (hIOVA) to map
> onto the physical doorbell (hDB).
> 
> So we end up with 2 untied mappings:
>          S1            S2
> gIOVA    ->    gDB
>               hIOVA    ->    hDB
> 
> Currently the PCI device is programmed by the host with hIOVA
> as MSI doorbell. So this does not work.
> 
> This patch introduces an API to pass gIOVA/gDB to the host so
> that gIOVA can be reused by the host instead of re-allocating
> a new IOVA. So the goal is to create the following nested mapping:
Does the gDB can be reused under non-nested mode?

> 
>          S1            S2
> gIOVA    ->    gDB     ->    hDB
> 
> and program the PCI device with gIOVA MSI doorbell.
> 
> In case we have several devices attached to this nested domain
> (devices belonging to the same group), they cannot be isolated
> on guest side either. So they should also end up in the same domain
> on guest side. We will enforce that all the devices attached to
> the host iommu domain use the same physical doorbell and similarly
> a single virtual doorbell mapping gets registered (1 single
> virtual doorbell is used on guest as well).
> 
[...]

> + *
> + * The associated IOVA can be reused by the host to create a nested
> + * stage2 binding mapping translating into the physical doorbell used
> + * by the devices attached to the domain.
> + *
> + * All devices within the domain must share the same physical doorbell.
> + * A single MSI GIOVA/GPA mapping can be attached to an iommu_domain.
> + */
> +
> +int iommu_bind_guest_msi(struct iommu_domain *domain,
> +			 dma_addr_t giova, phys_addr_t gpa, size_t size)
> +{
> +	if (unlikely(!domain->ops->bind_guest_msi))
> +		return -ENODEV;
> +
> +	return domain->ops->bind_guest_msi(domain, giova, gpa, size);
> +}
> +EXPORT_SYMBOL_GPL(iommu_bind_guest_msi);
> +
> +void iommu_unbind_guest_msi(struct iommu_domain *domain,
> +			    dma_addr_t iova)
nit: s/iova/giova

> +{
> +	if (unlikely(!domain->ops->unbind_guest_msi))
> +		return;
> +
> +	domain->ops->unbind_guest_msi(domain, iova);
> +}
> +EXPORT_SYMBOL_GPL(iommu_unbind_guest_msi);
> +
[...]

Thanks,
Keqian