Hi Marc, On 02/18/2016 05:51 PM, Marc Zyngier wrote: > On 18/02/16 16:42, Eric Auger wrote: >> Hello, >> On 02/18/2016 12:06 PM, Marc Zyngier wrote: >>> On Fri, 12 Feb 2016 08:13:09 +0000 >>> Eric Auger <eric.auger@xxxxxxxxxx> wrote: >>> >>>> This patch introduces iommu_get/put_single_reserved. >>>> >>>> iommu_get_single_reserved allows to allocate a new reserved iova page >>>> and map it onto the physical page that contains a given physical address. >>>> It returns the iova that is mapped onto the provided physical address. >>>> Hence the physical address passed in argument does not need to be aligned. >>>> >>>> In case a mapping already exists between both pages, the IOVA mapped >>>> to the PA is directly returned. >>>> >>>> Each time an iova is successfully returned a binding ref count is >>>> incremented. >>>> >>>> iommu_put_single_reserved decrements the ref count and when this latter >>>> is null, the mapping is destroyed and the iova is released. >>> >>> I wonder if there is a requirement for the caller to find out about the >>> size of the mapping, or to impose a given size... MSIs clearly do not >>> have that requirement (this is always a 32bit value), but since. >>> allocations usually pair address and size, I though I'd ask... >> Yes. Currently this only makes sure the host PA is mapped and returns >> the corresponding IOVA. It is part of the discussion we need to have on >> the API besides the problematic of which API it should belong to. > > One of the issues I have with the API at the moment is that there is no > control on the page size. Imagine you have allocated a 4kB IOVA window > for your MSI, but your IOMMU can only map 64kB (not unreasonable to > imagine on arm64). What happens then? The code checks the IOVA window size is aligned with the IOMMU page size so I think that case is handled at iova domain creation (arm_smmu_alloc_reserved_iova_domain). > > Somehow, userspace should be told about it, one way or another. I agree on that point. The user-space should be provided with the information about the requested iova pool size and alignments. This is missing in current rfc series. Best Regards Eric > > Thanks, > > M. > -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
