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Subject: Re: [PATCH v13 02/15] iommu: Introduce bind/unbind_guest_msi
To:     Auger Eric <eric.auger@redhat.com>, <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>, <joro@8bytes.org>, <maz@kernel.org>,
        <robin.murphy@arm.com>, <alex.williamson@redhat.com>
References: <20201118112151.25412-1-eric.auger@redhat.com>
 <20201118112151.25412-3-eric.auger@redhat.com>
 <6a70d93d-329f-4129-bd90-03f8589c5de4@huawei.com>
 <1ef4f5ae-9ca6-7c6d-f8a9-31240e5688c2@redhat.com>
CC:     <jean-philippe@linaro.org>, <jacob.jun.pan@linux.intel.com>,
        <nicoleotsuka@gmail.com>, <vivek.gautam@arm.com>,
        <yi.l.liu@intel.com>, <zhangfei.gao@linaro.org>
From:   Keqian Zhu <zhukeqian1@huawei.com>
Message-ID: <bc7b223e-7c30-9baa-85e3-2195e03dfe48@huawei.com>
Date:   Thu, 18 Feb 2021 16:43:43 +0800
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Hi Eric,

On 2021/2/12 16:55, Auger Eric wrote:
> Hi Keqian,
> 
> On 2/1/21 12:52 PM, Keqian Zhu wrote:
>> 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?
> 
> Under non nested mode the hIOVA is allocated within the MSI reserved
> region exposed by the SMMU driver, [0x8000000, 80fffff]. see
> iommu_dma_prepare_msi/iommu_dma_get_msi_page in dma_iommu.c. this hIOVA
> is programmed in the physical device so that the physical SMMU
> translates it into the physical doorbell (hDB = host physical ITS
So, AFAIU, under non-nested mode, at smmu side, we reuse the workflow of non-virtualization scenario.

> doorbell). The gDB is not used at pIOMMU programming level. It is only
> used when setting up the KVM irq route.
> 
> Hope this answers your question.
Thanks for your explanation!
> 

Thanks,
Keqian

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