Re: [RFC PATCH v2 1/2] vfio/type1: Adopt fast IOTLB flush interface when unmap IOVAs

[Suravee Suthikulpanit]

Hi Alex,

On 1/9/18 4:07 AM, Alex Williamson wrote:

@@ -661,6 +705,8 @@ static long vfio_unmap_unpin(struct vfio_iommu *iommu, 
struct vfio_dma *dma,
        if (!IS_IOMMU_CAP_DOMAIN_IN_CONTAINER(iommu))
                return 0;

+ INIT_LIST_HEAD(&unmapped_regions);

+
        /*
         * We use the IOMMU to track the physical addresses, otherwise we'd
         * need a much more complicated tracking system.  Unfortunately that
@@ -698,24 +744,36 @@ static long vfio_unmap_unpin(struct vfio_iommu *iommu, 
struct vfio_dma *dma,
                                break;
                }

- unmapped = iommu_unmap(domain->domain, iova, len);

-               if (WARN_ON(!unmapped))
+               entry = kzalloc(sizeof(*entry), GFP_KERNEL);
+               if (!entry)
                        break;

Turns out this nagged at me a bit too, this function only gets called
once to dump the vfio_dma, so bailing out here leaves pages pinned and
IOMMU mappings in place, for a performance optimization that we could
just skip.  We could sync&unpin anything collected up to this point and
continue this step with a synchronous unmap/unpin.  Thanks,

Ah, that's an over look in my part also. Thanks for catching this. I'll 
implement
the fallback mechanism per your suggestion in v3.

Thanks,
Suravee