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SubjectRe: [PATCH 1/2] vfio/type1: Adopt fast IOTLB flush interface when unmap IOVAs
On Fri, 17 Nov 2017 15:11:19 -0600
Suravee Suthikulpanit <Suravee.Suthikulpanit@amd.com> wrote:

> From: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
>
> VFIO IOMMU type1 currently upmaps IOVA pages synchronously, which requires
> IOTLB flushing for every unmapping. This results in large IOTLB flushing
> overhead when handling pass-through devices with a large number of mapped
> IOVAs (e.g. GPUs).

Of course the type of device is really irrelevant, QEMU maps the entire
VM address space for any assigned device.

> This can be avoided by using the new IOTLB flushing interface.
>
> Cc: Alex Williamson <alex.williamson@redhat.com>
> Cc: Joerg Roedel <jroedel@suse.de>
> Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
> ---
> drivers/vfio/vfio_iommu_type1.c | 12 +++++++++---
> 1 file changed, 9 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
> index 92155cc..28a7ab6 100644
> --- a/drivers/vfio/vfio_iommu_type1.c
> +++ b/drivers/vfio/vfio_iommu_type1.c
> @@ -698,10 +698,12 @@ static long vfio_unmap_unpin(struct vfio_iommu *iommu, struct vfio_dma *dma,
> break;
> }
>
> - unmapped = iommu_unmap(domain->domain, iova, len);
> + unmapped = iommu_unmap_fast(domain->domain, iova, len);
> if (WARN_ON(!unmapped))
> break;
>
> + iommu_tlb_range_add(domain->domain, iova, len);
> +

We should only add @unmapped, not @len, right?

> unlocked += vfio_unpin_pages_remote(dma, iova,
> phys >> PAGE_SHIFT,
> unmapped >> PAGE_SHIFT,
> @@ -710,6 +712,7 @@ static long vfio_unmap_unpin(struct vfio_iommu *iommu, struct vfio_dma *dma,
>
> cond_resched();
> }
> + iommu_tlb_sync(domain->domain);
>
> dma->iommu_mapped = false;
> if (do_accounting) {
> @@ -884,8 +887,11 @@ static int map_try_harder(struct vfio_domain *domain, dma_addr_t iova,
> break;
> }
>
> - for (; i < npage && i > 0; i--, iova -= PAGE_SIZE)
> - iommu_unmap(domain->domain, iova, PAGE_SIZE);
> + for (; i < npage && i > 0; i--, iova -= PAGE_SIZE) {
> + iommu_unmap_fast(domain->domain, iova, PAGE_SIZE);
> + iommu_tlb_range_add(domain->domain, iova, PAGE_SIZE);
> + }
> + iommu_tlb_sync(domain->domain);
>
> return ret;
> }

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