Re: [RFC v3 03/21] iommu: Introduce bind_guest_msi

Auger Eric
2019-01-25T18:11:50Z

Hi Alex,

On 1/11/19 11:44 PM, Alex Williamson wrote:
> On Tue, 8 Jan 2019 11:26:15 +0100
> Eric Auger <eric.auger@redhat.com> 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 -> gDB
> ^^^ 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:
>>
>> S1 S2
>> gIOVA -> gDB -> hDB
>>
>> and program the PCI device with gIOVA MSI doorbell.
>>
>> Signed-off-by: Eric Auger <eric.auger@redhat.com>
>>
>> ---
>>
>> v2 -> v3:
>> - add a struct device handle
>> ---
>> drivers/iommu/iommu.c | 10 ++++++++++
>> include/linux/iommu.h | 13 +++++++++++++
>> include/uapi/linux/iommu.h | 6 ++++++
>> 3 files changed, 29 insertions(+)
>>
>> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
>> index b2e248770508..ea11442e7054 100644
>> --- a/drivers/iommu/iommu.c
>> +++ b/drivers/iommu/iommu.c
>> @@ -1431,6 +1431,16 @@ static void __iommu_detach_device(struct iommu_domain *domain,
>> trace_detach_device_from_domain(dev);
>> }
>>
>> +int iommu_bind_guest_msi(struct iommu_domain *domain, struct device *dev,
>> + struct iommu_guest_msi_binding *binding)
>> +{
>> + if (unlikely(!domain->ops->bind_guest_msi))
>> + return -ENODEV;
>> +
>> + return domain->ops->bind_guest_msi(domain, dev, binding);
>> +}
>> +EXPORT_SYMBOL_GPL(iommu_bind_guest_msi);
>> +
>> void iommu_detach_device(struct iommu_domain *domain, struct device *dev)
>> {
>> struct iommu_group *group;
>> diff --git a/include/linux/iommu.h b/include/linux/iommu.h
>> index 96d59886f230..244c1a3d5989 100644
>> --- a/include/linux/iommu.h
>> +++ b/include/linux/iommu.h
>> @@ -235,6 +235,9 @@ struct iommu_ops {
>> int (*cache_invalidate)(struct iommu_domain *domain, struct device *dev,
>> struct iommu_cache_invalidate_info *inv_info);
>>
>> + int (*bind_guest_msi)(struct iommu_domain *domain, struct device *dev,
>> + struct iommu_guest_msi_binding *binding);
>> +
>> unsigned long pgsize_bitmap;
>> };
>>
>> @@ -301,6 +304,9 @@ extern int iommu_set_pasid_table(struct iommu_domain *domain,
>> extern int iommu_cache_invalidate(struct iommu_domain *domain,
>> struct device *dev,
>> struct iommu_cache_invalidate_info *inv_info);
>> +extern int iommu_bind_guest_msi(struct iommu_domain *domain, struct device *dev,
>> + struct iommu_guest_msi_binding *binding);
>> +
>> extern struct iommu_domain *iommu_get_domain_for_dev(struct device *dev);
>> extern struct iommu_domain *iommu_get_dma_domain(struct device *dev);
>> extern int iommu_map(struct iommu_domain *domain, unsigned long iova,
>> @@ -724,6 +730,13 @@ iommu_cache_invalidate(struct iommu_domain *domain,
>> return -ENODEV;
>> }
>>
>> +static inline
>> +int iommu_bind_guest_msi(struct iommu_domain *domain, struct device *dev,
>> + struct iommu_guest_msi_binding *binding)
>> +{
>> + return -ENODEV;
>> +}
>> +
>> #endif /* CONFIG_IOMMU_API */
>>
>> #ifdef CONFIG_IOMMU_DEBUGFS
>> diff --git a/include/uapi/linux/iommu.h b/include/uapi/linux/iommu.h
>> index 4605f5cfac84..f28cd9a1aa96 100644
>> --- a/include/uapi/linux/iommu.h
>> +++ b/include/uapi/linux/iommu.h
>> @@ -142,4 +142,10 @@ struct iommu_cache_invalidate_info {
>> __u64 arch_id;
>> __u64 addr;
>> };
>> +
>> +struct iommu_guest_msi_binding {
>> + __u64 iova;
>> + __u64 gpa;
>> + __u32 granule;
>
> What's granule? The size? This looks a lot like just a stage 1
> mapping interface, I can't really figure out from the description how
> this matches to any specific MSI mapping. Zero comments in the code
> or headers here about how this is supposed to work. Thanks,
Considering your next comment about the unbind() operation, I think the
struct can simply be removed. Instead we could directly have:
int (*bind_guest_msi)(struct iommu_domain *domain, struct device *dev,
dma_addr_t iova, gpa_t gpa, size_t size);
int (*unbind_guest_msi)(struct iommu_domain *domain, struct device *dev,
dma_addr_t iova);

Thanks

Eric
>
> Alex
>