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

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Message-ID: <96edcdf3-baec-7432-529a-567a221d60a3@redhat.com>
Date:   Thu, 18 Feb 2021 11:35:44 +0100
From:   Auger Eric <eric.auger@...hat.com>
To:     Keqian Zhu <zhukeqian1@...wei.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 Keqian,

On 2/18/21 9:43 AM, Keqian Zhu wrote:
> 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.
Without virtualization, the host kernel also transparently allocates an
iova to map the doorbell. With standard passthrough withou vIOMMU, the
iova window is different (MSI RESV region).

Thanks

Eric
> 
>> 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
>>
>> .
>>
>