Re: [PATCH v13 02/15] iommu: Introduce bind/unbind_guest_msi

[Auger Eric]

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
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.

> 
>>
>>          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