Re: [Qemu-devel] [PATCH v7 03/17] vfio: allow to notify unmap for very large region

[David Gibson <david@gibson.dropbear.id.au>]

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On Tue, Feb 07, 2017 at 04:28:05PM +0800, Peter Xu wrote:
> Linux vfio driver supports to do VFIO_IOMMU_UNMAP_DMA for a very big
> region. This can be leveraged by QEMU IOMMU implementation to cleanup
> existing page mappings for an entire iova address space (by notifying
> with an IOTLB with extremely huge addr_mask). However current
> vfio_iommu_map_notify() does not allow that. It make sure that all the
> translated address in IOTLB is falling into RAM range.
> 
> The check makes sense, but it should only be a sensible checker for
> mapping operations, and mean little for unmap operations.
> 
> This patch moves this check into map logic only, so that we'll get
> faster unmap handling (no need to translate again), and also we can then
> better support unmapping a very big region when it covers non-ram ranges
> or even not-existing ranges.
> 
> Acked-by: Alex Williamson <alex.williamson@redhat.com>
> Signed-off-by: Peter Xu <peterx@redhat.com>

Reviewed-by: David Gibson <david@gibson.dropbear.id.au>

Seems sensible of itself, except that I don't understand how we were
ever working before this.

> ---
>  hw/vfio/common.c | 7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)
> 
> diff --git a/hw/vfio/common.c b/hw/vfio/common.c
> index 42c4790..f3ba9b9 100644
> --- a/hw/vfio/common.c
> +++ b/hw/vfio/common.c
> @@ -352,11 +352,10 @@ static void vfio_iommu_map_notify(IOMMUNotifier *n, IOMMUTLBEntry *iotlb)
>  
>      rcu_read_lock();
>  
> -    if (!vfio_get_vaddr(iotlb, &vaddr, &read_only)) {
> -        goto out;
> -    }
> -
>      if ((iotlb->perm & IOMMU_RW) != IOMMU_NONE) {
> +        if (!vfio_get_vaddr(iotlb, &vaddr, &read_only)) {
> +            goto out;
> +        }
>          /*
>           * vaddr is only valid until rcu_read_unlock(). But after
>           * vfio_dma_map has set up the mapping the pages will be

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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